Historical and Future Ozone Simulations
using the MM5/SMOKE/CMAQ System
in the Portland/Vancouver Area

                                  Prepared by

                            Ying Xie and Brian Lamb
                      Laboratory for Atmospheric Research
              Department of Civil & Environmental Engineering
                          Washington State University

                                 Prepared for

                  Oregon Department of Environmental Quality
                          Southwest Clean Air Agency
                    Washington State Department of Ecology

                               December 31, 2005
                               Table of contents
1 Executive Summary	3
2 Introduction	5
3 Ozone Modeling Study Goal and Design	5
3.1 Previous Ozone Modeling Work	5
3.1.1 Maintenance Plan EKMA modeling	6
3.1.2 Southwest Washington Ozone Study	6
3.1.3 NW Regional Technical Center Demonstration Project	6
4 Episode Selection	7
5 Meteorological modeling	9
5.1 Modeling methods	9
5.2 Meteorological modeling results and evaluation (July 1998 episode)	12
5.2.1 Surface Temperature	12
5.2.2 Surface winds	16
5.2.3 Soil moisture	19
5.2.4 PBL height and vertical profile	21
5.2.5 MM5 statistical evaluation	27
5.2.6 LSM run compared with simple soil model run	28
5.3 Modeling results and evaluation (July 1997 episode)	29
5.4 Back trajectory analysis	35
6 Photochemical air quality modeling	37
6.1 Modeling methods	37
6.2 CMAQ modeling results and evaluation (July 1998 episode)	39
6.2.1 CMAQ statistics evaluation	47
6.2.2 Comparisons with NOx/VOC monitoring data	52
6.3 CMAQ modeling results and evaluation (July 1997 episode)	58
6.3.1 CMAQ statistics evaluation	64
6.3.2 Comparisons with NOx monitoring data	69
6.4 Conclusion for July 1998 and 1997 CMAQ simulation	76
7 Future episode modeling (2015)	76
7.1 Future year base case	76
7.1.1 CMAQ modeling results	76
7.1.2 VOC/NOx ratios and regional increase of ozone	83
7.2 What if scenario - No lower Columbia River point sources	86
Reference	93
Appendix A. Emission Inventory Documentation	95
Appendix B: Area Source Category Emission Calculation Methodologies	108
Appendix C: MOBILE6.2 input files for the 1997 and 1998 episodes.	111
Appendix D:  Acronyms	125

1 Executive Summary

In order to develop quantitative estimates of ozone levels in future years, a modeling study was completed for the Portland, OR, and Vancouver, WA urban region.  This work was conducted as part of the State Implementation Plan development for this area.  Two historical episodes (July 17-21, 1997 and July 26-28, 1998) were simulated using the Mesoscale Meteorological model version 5/ Sparse Matrix Operator Kernel Emissions Modeling System / Community Multi-scale Air Quality Modeling System (MM5/SMOKE/CMAQ).  These two episodes were selected for this modeling work because the July 1998 episode had the highest ozone levels observed in recent years for the airshed and the July 1997 episode had slightly different meteorological patterns compared to the 1998 case.  In addition to the normal ozone observations, VOC/NOx monitoring data were also available for the July 1997 episode for comparison to the modeled results.

As part of the base simulation for the July 1998 episode, tests were conducted to investigate the effects of using a more complex land-surface modeling option -- the Noah Land Surface Model, LSM -- within the MM5 meteorological model.  In these tests, using the LSM in MM5 produced a better simulation of surface temperatures and generally lower and more accurate planetary boundary layer (PBL) heights along the west side of the Cascades compared to using the traditional simple soil model.  As a result, air quality modeling results for ozone were also improved using MM5 with the LSM option.  For the CMAQ simulation, model performance statistics for most monitoring sites were within United States Environmental Protection Agency (EPA) suggested 1-hr and 8-hr ozone modeling guidelines.  Time series plots, scatter plots, and Quantile-Quantile plots also showed generally good agreement between model simulations and observations. .While model performance was acceptable for both episodes, the July 1998 episode was selected as the base for evaluation of future year (2015) managed growth maintenance projection simulations because observed ozone concentrations were much higher in 1998.
Two 2015 managed growth maintenance projection simulations were modeled. The first simulation analyzed changes in ozone formation with the emissions inventory changes in the future. The second simulation was a modification of the first designed to examine the influence of the industrial sources located along the lower Columbia River on the ozone formation in the Portland/Vancouver urban area.

The future year (2015) emission inventory was developed using growth factors depending on the surrogates for each source category.  Federally mandated control strategies and foreseeable changes were also taken into account.   Total emissions for all pollutants were projected to decrease in the 2015 emissions inventory compared to the 1998 emissions inventory.  Furthermore, NOx emissions were projected to have a greater reduction than VOC emissions which resulted in an increase of the VOC/NOx emission ratio.  For 1998, the entire Portland urban area and I-5 corridor appeared to be in the VOC-sensitive region, based upon predicted O3/NOx concentration ratios.  For 2015, the VOC-sensitive areas were much smaller, which is consistent with the increased VOC/NOx ratio.  A large reduction in ozone was predicted to occur downwind of urban Portland in 2015 CMAQ simulation results compared to the 1998 modeling results.  The reduction of ozone levels within the urban core was less significant than at the downwind sites.  The second projected 2015 simulation which  assumed no large industrial activity along the lower Columbia River showed  reductions up to 12 ppb at the southwestern Washington observation sites when compared to the first 2015 managed growth maintenance projection;  sites in Oregon showed small or no differences associated with this simulation.

Further analysis of other potential control strategies, based upon modifications to the 2015 managed growth maintenance projection, will be conducted by ODEQ and SWCAA as part of the overall maintenance plan development.

2 Introduction

The current 1-Hour Ozone Maintenance Plans for the Portland/Vancouver airshed were adopted as part of the Oregon and Washington State Implementation Plans in 1997.  The control measures in those plans have helped the region maintain the now-revoked 1-hour ozone National Ambient Air Quality Standard (NAAQS).  The region is also in attainment of the 8-hour ozone NAAQS, the current ozone standard.

However, due to exceedances of the 1-hour ozone standard in the recent past, the unique meteorological influences from the Columbia River Gorge, and the potential for ozone precursor transport in the region, regional air regulatory agencies proposed performance of photochemical modeling for the area as a basis for improving our understanding of the potential for ozone exceedances in the future.  This report presents the results of this modeling study.  The modeling system used for this work was the MM5/SMOKE/CMAQ system; it was applied to a domain consisting of 4 km x 4 km horizontal grid cells covering an area that extended from north of Puget Sound to south of Salem, OR and from the Pacific coast on the west to beyond the Cascade Mountain range on the east.  The modeling work involved simulation of two historical episodes, July 17-21, 1997 and July 26-28, 1998.  The model results were compared to available observations, and then the 1998 episode was used as a basis for evaluation of future year (2015) managed growth projections.  An important aspect of the modeling study was the evaluation of model sensitivity to use of different land/surface models within the MM5 meteorological model.  Results from these sensitivity studies are also described in this report.

3 Ozone Modeling Study Goal and Design

The overall goal for this work was to improve understanding of ozone behavior in the Portland/Vancouver airshed and to obtain model results to help evaluate future year conditions and the effectiveness of potential control strategies.  The approach involved the following steps:  1) selection of suitable ozone episodes that represented worst-case or typical ozone conditions, 2) development of the necessary meteorological, emissions, and air quality observations data sets, 3) optimization of the modeling system to yield acceptable model performance for these episodes, and 4) use of the meteorological simulation from one of these episodes as a basis for evaluation of future year conditions and control strategy effectiveness.  This work was guided by the Portland/Vancouver ozone modeling technical committee consisting of representatives from Oregon Department of Environmental Quality (ODEQ), Southwest Clean Air Agency (SWCAA), Washington State Department of Ecology (Ecology), the U.S. Environmental Protection Agency (EPA), and Washington State University (WSU).

3.1 Previous Ozone Modeling Work
There have been only limited ozone modeling efforts for the Portland/Vancouver area.  The 1990 Clean Air Act (CAA) Amendments classified the Portland/Vancouver airshed as a marginal ozone nonattainment area.  There is no CAA requirement for a marginal ozone nonattainment area to perform photochemical modeling or any other attainment demonstration.  Furthermore, there have not been other federal requirements for air regulatory agencies to perform ozone air quality modeling in the Portland/Vancouver airshed.  The only ozone modeling work that has been performed has been a result of special project work or large-scale regional modeling efforts that included the Portland/Vancouver airshed in the overall domain.

3.1.1 Maintenance Plan EKMA modeling
The redesignation request/ozone maintenance plans that were submitted to the Oregon and Washington SIPs in 1996 relied on historical ozone monitoring data, future control measures, and emission inventory projections to demonstrate future attainment with the 1-hour ozone standard.  The ozone modeling work for that submittal was limited to a determination of emission levels necessary to prevent future exceedances using the Empirical Kinetics Modeling Approach (EKMA).  This work utilized the Ozone Isopleth Plotting Package with Optional Mechanisms (OSIPM-4) to conduct the EKMA analysis.

3.1.2 Southwest Washington Ozone Study
Following EPA's approval of the Portland and Vancouver ozone SIP submittals, WSU was contracted by Ecology and SWCAA to conduct a photochemical modeling study of the area to determine the potential effects of point sources upwind of the Portland/Vancouver maintenance area on the area's monitored ozone values.  The main purpose of the study was to address the question of the impact of the emissions from the major industrial point sources in Cowlitz County, WA on ozone levels in the Portland/Vancouver maintenance area.  This study also had an objective to help develop the regional photochemical modeling system.  This included running the MM5 prognostic weather model and the CALGRID/CALMET suite of models with a fine resolution grid (5 km).  The study focused on an ozone episode during July 11-14, 1996.  The final report for this study was published in January of 1999 and is available for review on the Ecology website.

3.1.3 NW Regional Technical Center Demonstration Project
This work was the result of a multi-agency collaborative effort to develop regional air quality modeling capabilities.  The contributing agencies for this work were EPA Region 10, Ecology, ODEQ, Idaho Department of Environmental Quality and Environment Canada.  The main goal of this project was to establish a virtual technical center and to demonstrate the use of the EPA CMAQ regional modeling system.  The agencies contracted with WSU to run several CMAQ and CALGRID runs with varying chemical mechanisms and MM5 grid scales.  This has been the most extensive modeling exercise that has encompassed the Portland/Vancouver region to date.  Several modeling runs were completed to look at ozone and visibility at a 12 km grid scale.  The model runs focused on two events,  July 2-14, 1996 and July 23-30, 1996.  The work was conducted from early 2000 to June 2002.  Further details are in O'Neill and Lamb (2004); O'Neill et al. (2005); and Chen (2002).

These ozone modeling studies provided the basis for the design of the current modeling project.  In particular, the demonstration and evaluation of CMAQ in these previous studies were very valuable for the current study.  Details describing the episode selection and modeling methods are given in the following sections.

4 Episode Selection

The Portland/Vancouver Maintenance Area has had relatively mild ozone seasons during the summers of 1999, 2000, 2001, and 2002.  There were monitored exceedances of the 1-hour ozone standard in 1996 and 1998.  There were also times of elevated ozone levels during most years when the standard was not exceeded.

General EPA guidance for episode selection recommends analyzing observed meteorological patterns to determine which have caused violations for the area in the past.  The Portland/Vancouver ozone modeling technical committee recommended modeling one scenario of each of the major meteorological situations that cause exceedances.

The following episodes were suggested as potential episodes to model.

 July 11-14, 1996 (Same episode used for the NWRTC Demonstration Project and the Southwest Ozone Study, one 1-hour ozone exceedance in the Portland area)
 July 22-31, 1998 (Series of 3 exceedances in the Portland area during the 25[th] through the 28[th])
 July 17-22, 1997 (Episode with moderate monitored values under the 8-hour standard at the Portland/Vancouver monitors but well monitored)
 July 22-26, 1996 (Episode with the highest ozone measurements in the area for 1996, 1997, and 1998)
 August 7-10, 1996 (Episode with Sauvie Island monitor reaching its highest value for 1996)

The Portland/Vancouver ozone modeling technical committee considered several factors during selection of the episodes to be modeled, including:

 Ozone episodes selected for modeling should be selected from the most frequent, typical, and representative patterns associated with high ozone in the region.
 Recent episodes are preferred over older episodes because recent episodes represent the current emissions inventory, including mobile and point configurations.  Recent episodes can also be more representative of current reduction strategies.
 Well-monitored episodes (with more meteorology, VOC, and NOx data) are preferred over data poor episodes. Additional data allow for more thorough model evaluation and provide information necessary to understand the processes leading to high ozone.
 Ozone episodes should be selected with high monitored values to represent the meteorology that results in severe ozone.  Furthermore, episodes should have high ozone in the geographical areas where high values typically occur. Such selection will allow modeling potential control strategies with representative ozone concentrations in the areas where the strategies must work.
 Multi-day episodes are the most efficient way to model both long range transport of ozone and the accumulation of local emissions that are associated with ozone.
 Multi-day episodes also allow the possibility of testing model responsiveness. If the model can reproduce both the high and low ozone days within a period, there will be more confidence in the model and its ability to replicate and forecast events.

The Portland/Vancouver ozone modeling technical committee screened the suggested episodes  based on the considerations listed above and recommended two episodes.  The recommended episodes are as follows:

July 22-31, 1998 was selected to be the first episode modeled.  The July 1998 episode accounted for 3 exceedances of both the 1-hour and 8-hour ozone standards at the Carus monitor in the Portland area within a short period of time.  There was also a near exceedance of the 1-hour standard and an exceedance of the 8-hour standard at the Milwaukie monitor.  There were elevated temperatures over the series of days and light NW winds.  The 1998 episode was chosen instead of the July 11-14, 1996 episode because considerable analysis has already been done for the 1996 episode, and there would be more benefit from analyzing a new episode.  Table 1 shows some select data from the 1998 episode.

Table 1: Selected peak ozone concentrations during the July 22-31, 1998 episode (ppb)

                                   Milwaukie
                                     Carus
Date
                                    1-hour
                                    8-hour
                                    1-hour
                                    8-hour
July 26
                                      124
                                      100
                                      136
                                      117
July 27

                                      133
                                      86
July 28

                                      137
                                      98

July 17-22, 1997 was selected to be the second episode modeled.  This episode did not coincide with any ozone standard exceedances; however there were moderately high ozone levels recorded at the Milwaukie monitor.  This episode also seemed to show a slightly different meteorological pattern than the 1998 episode as indicated by moderate values at both the Vancouver and Carus sites.  The modeling technical committee compared this episode with the July 11-14, 1996 episode and decided that it would be more beneficial to focus the efforts on an event that has not previously been analyzed with a model in this area.  Another reason for the selection of this episode (as opposed to 1996) is that there are additional monitoring data for southwest Washington obtained during an Ecology study conducted in the summer of 1997, 1998, and part of 1999.  In addition to the meteorological and ozone data on the Oregon side, in both 1998 and 1997, Southwest WA had four ozone sites in the domain (Woodland, Mt. View, Castle Rock, and Hockinson), and three NOx sites (Castle Rock, Mt.View and Woodland).  Additionally, in 1997 HC and carbonyl measurements were taken at Castle Rock and Mt.View and there was one additional met site at a Bonneville Power Administration site.  This additional monitoring in 1997 contrasts with the usual situation in southwest Washington where there is a lack of NOx and VOC sites and only a single ozone site.  Table 2 shows some select data from the 1997 episode.

Table 2: Summary of the July 17-22, 1997 episode ozone values (ppb)

                             Mt. View (Vancouver)
                                   Milwaukie
                                     Carus
                                 Sauvie Island
Date
                                    1-hour
                                    8-hour
                                    1-hour
                                    8-hour
                                    1-hour
                                    8-hour
                                    1-hour
                                    8-hour
July 19
                                      59
                                      53
                                      65
                                      55
                                      77
                                      65
                                      59
                                      52
July 20
                                      77
                                      62
                                      101
                                      73
                                      73
                                      68
                                      48
                                      38

5 Meteorological modeling

5.1 Modeling methods
The Mesoscale Meteorological model Version 5 (MM5, Grell et al., 1994) was used to provide the 3-D meteorological field for air quality modeling.  Three one-way nested domains with grid cell horizontal sizes of 36 km, 12 km, and 4 km were applied.  The two outer domains consisted of 98x95 and 133x151 grid cells, respectively.  The innermost domain consisted of 112x112 grid cells which extended from north of Puget Sound in Washington to south of Salem, OR and from the Pacific coast on the west to beyond the Cascade Mountain range on the east.  This domain was larger than the immediate area of Portland/Vancouver and was selected to minimize the influence of boundary conditions.  Vertically, 38 sigma layers were specified. The 12 km and 4 km MM5 domains are shown in Figure 1.

To obtain meteorological fields that produced acceptable results with CMAQ in terms of ozone performance, several MM5 runs with different physics configurations were conducted as shown in Table 3.

Table 3. MM5 configuration used for different model runs
                                     Runs
                             5-layer soil model_1
                              5-layer soil mode_2
                                     LSM_1
                                     LSM_2
                                     Label
                                     "_o"
                                  "base_sen"
                                 "sen_ini_LSM"
                               "sen_ini_LSM_ns"
                                Initialization
                                  NCEP GDAS
                                    ETA212
                                    ETA212
                                    ETA212
                                   Radiation
                                Cloud-radiation
                                CCM2 Radiation
                                Cloud-radiation
                                Cloud-radiation
                                   Moisture
                                  Simple ice
                                   Reisner 2
                                  Simple ice
                                  Simple ice
                                Surface scheme
                              5-layer soil model
                              5-layer soil model
                                   Noah LSM
                                   Noah LSM
                                Cumulus scheme
                                  KF Cumulus
                                  KF Cumulus
                                  KF Cumulus
                                  KF Cumulus
                                  PBL  scheme
                                      MRF
                                      MRF
                                      MRF
                                      MRF
           Analysis nudging of Tsfc and winds within boundary layer
                                 Not turned on
                                 Not turned on
                                 Not turned on
                                   Turned on

As described later, the "LSM_1" run produced the best overall results for air quality modeling.  In this report, this run is evaluated and compared with the original run ("5-layer soil model_1").  The original 5-layer soil model run was initialized using NCEP Global Data Assimilation System (GDAS) analysis archived on a 2.5x2.5 degree lat/long grid at every 12 hours.  All other runs were initialized using NCEP Eta model analysis archived on a 40 km grid at every 3hrs.  Analysis nudging was applied in the coarse domains (36 km, 12 km) and observational nudging was applied in the inner 4km domain.  For analysis nudging, 3D nudging was employed for winds, temperature, and moisture above the PBL.  Surface nudging was applied for winds and moisture, but not temperature. In some sensitivity runs, boundary layer 3D nudging was turned on for winds and surface nudging was also turned on for temperature.  See Table 3 for configuration details.  Wind speed and direction observations from about 20 surface stations were used for observational nudging of the winds in the inner 4 km domain.  A map of these stations is shown in Figure 2.  Data from four surface stations (Ecology sites as shown in Figure 2) were withheld from the nudging analysis so that an independent evaluation could be conducted at these sites.  For all runs, land use data were derived from 1 km USGS global terrain and land use database.

The MM5 physics options used in the LSM run included use of the Kain-Fritsch cumulus parameterization scheme (Kain and Fritsch, 1993), the MRF PBL scheme (Hong and Pan, 1996), simple ice moisture, cloud-radiation, and Noah Land Surface Model (Chen and Dudhia, 2001).  In some sensitivity runs, CCM2 radiation, Reisner2 moisture, and the 5-layer soil model were employed as shown in Table 3.  It should be noted that the current configuration used in the University of Washington MM5 forecast system matches the configuration of the soil model run with the CCM2 radiation and Reisner2 moisture treatment.

                Figure 1. 12 and 4 km MM5 domain (D03 and D04)

Figure2. Surface stations used in MM5 observational nudging. The stations within the box outlined in blue were used in nudging (expect for four ecology sites which were withheld).  The sites within the inner box outlined in green were used in model evaluation.

It has been shown that soil moisture has a significant impact on PBL parameters such as surface temperature and PBL height (Zhang and Anthes, 1982).  These processes as well as cloud coverage, profiles of humidity, temperature and wind are all related to surface wetness and vegetation cover (Xiu and Pleim, 2001).  In the traditional MM5 approach (5-layer soil model), soil moisture is set to constant seasonal values depending on land use type.  Therefore, the effects of precipitation and evaporation are not treated explicitly.  In contrast, the Noah LSM has four soil layers with the thickness of 0.1, 0.3, 0.6, and 1.0 m.  It employs one canopy layer and prognostically solves for soil moisture and temperatures in each soil layer.  As a result, the LSM has the ability to account for temporal and spatial changes in soil moisture due to precipitation and evapo-transpiration effects.

5.2 Meteorological modeling results and evaluation (July 1998 episode)
5.2.1 Surface Temperature
Surface temperature contours from the simple soil-1 and LSM-1 runs are shown in Figure 3a and 3b at 17 PDT on July 28, 1998.  For western Washington and Oregon, the LSM run predicted cooler surface temperatures than the simple soil model, with only a small area around Portland above 35 C.  In the simple soil model, the warm areas were much more extensive around the Puget Sound area and from Portland to Salem.  In eastern Washington, the temperature patterns were opposite, where LSM-1 simulated warmer conditions than the simple soil model.

Predicted surface temperature and cloud coverage were compared with observations as shown in Figure 4a-c.  It appears that on the high ozone days (July 26 to July 28), the daily maximum temperatures predicted by both the LSM-1 and simple soil-1 models were fairly close to the observations at Portland and Salem.  On the low ozone days (July 23 to July 25), LSM-1 showed better agreement with the observations which might be related to improved simulation of clouds on these days.  However, in the northwestern part of the domain, such as at Castle Rock(Figure 4c), diurnal variations of surface temperature in LSM-1 were too small compared to the daily variations in the observations.  Similar patterns could also be found at some southwest sites such as UAO and HIO (not shown).  A scatter plot (Figure 5) showed that both model runs tended to overestimate low temperatures and underestimate high temperatures.  However, LSM-1 had slightly better agreement with the observations especially for the peak temperatures.

                                  Figure 2a.
Figure 3a. Surface temperature pattern from simple soil model run for 17:00 PDT on July 28, 1998.

Figure 3b.. Surface temperature pattern from LSM model run for 17:00 PDT on July 28, 1998.

Figure 4a. Surface temperature and cloud cover time series predicted by LSM and simple soil model compared with observations at Portland.
Figure 4b. Surface temperature and cloud cover time series predicted by LSM and simple soil model compared with observations at Salem.

Figure 4c. Surface temperature and cloud cover time series predicted by LSM and simple soil model compared with observations at Castle Rock.

Figure 5. Scatter plot of predicted surface temperature (LSM and simple soil) and observations from all available surface stations

5.2.2 Surface winds
Surface wind patterns are shown in Figure 6a, and 6b for 17 PDT on July 28.  The LSM-1 run predicted northerly winds along the I-5 corridor in western Washington, which veered to northwesterly and moved through the Portland area.  As the flow went further south, there was some apparent convergence with the strong southwesterly onshore flow along the Oregon coast.  In contrast, the winds from the simple soil model run showed very consistent northwesterly winds along the I-5 corridor.  The onshore winds along the Oregon coast flowed northwesterly instead of southwesterly as in the LSM-1 run.  Similar southwesterly onshore flows were also seen in other runs initialized using the Eta analysis, so this might be more related to the difference in initialization than in the surface scheme.

The MM5 first layer (38 m) winds were extrapolated to 10 m using the neutral logarithmic wind speed profile and compared with 10 m surface station observations as shown in Figure 7.  Predicted wind speed and direction showed reasonable agreement with the observations.  Both runs tended to underestimate the daytime surface winds (Figure 7a, 7b, and 7c).  This problem is well known for the MRF PBL scheme (Liu et al. 2004; Zhang et al. 2004.) and was related either to the underestimation of downward momentum flux or to the overestimation of friction velocity according to these researchers.

Figure 6a. Surface wind pattern from simple soil model run for 17:00 PDT on July 28, 1998.

Figure 6b. Surface wind pattern from LSM run for 17:00 PDT on July 28, 1998.

Figure 7a. Surface wind speed and wind direction time series predicted by LSM and simple soil model compared with observations at Portland
Figure 7b. Surface wind speed and wind direction time series predicted by LSM and simple soil model compared with observations at Salem.

Figure 7c. Surface wind speed and wind direction time series predicted by LSM and simple soil model compared with observations at Castle Rock.

5.2.3 Soil moisture
In the simple soil model, soil moisture has constant seasonal values (summer or winter) defined as a function of land use type.  Consequently, in summer most areas on the west side of the domain had volumetric soil moisture values of 0.3, except for urban areas where the soil moisture equaled 0.1.  On the east side of the Cascades, most areas were much drier with soil moisture of 0.1 except for the irrigated land (shown in Figure 8) where soil moistures were equal to 0.5.

In the LSM-1 run, soil moisture was initialized using analysis fields from the Eta model and solved prognostically.  Figure 8 shows the predicted values from LSM-1 at 17 PDT on July 27. Soil moisture for each layer (0.1, 0.3, 0.6, and 1 m) is shown.  It appears that soil was driest at the surface layer, and had more water in the deeper layers.  On the west side of the Cascades, soil moisture varied from 0.25 at the surface to 0.3 in the deeper layers.  The difference was more substantial on the east side of the Cascades where the water content varied from about 0.1 in the first layer to about 0.3 at 1 m deep.  Some wet areas in the shallow soil layer are obvious in the lower right corner of the domain; these were the result of convective rain storms simulated in this run.

Modeled soil moisture was also compared with the observations at the Wind River Canopy Crane research site located north of Stevenson, WA approximately 30 km from the Columbia River.  As described on the research site web page (http://cdiac.ornl.gov/ftp/ameriflux/data/us-sites/preliminary-data/Wind-River/1998/WRCCRF_met_meta_data.html), the observed values were measured at 30 cm using Campbell Scientific CS-615 probes.  The station is located in an old growth forest canopy where soil moisture can be highly heterogeneous (personal communication, Timothy Link).  However, the LSM-1 captured the drying trend in the observations fairly well (Figure 9).  Note that this is consistent with the fact that there was little rainfall during the episode for most of the domain, and therefore, soil moisture was mainly controlled by evapotranspiration.

Figure 8. Volumetric soil moisture defined in the simple soil model and values calculated in the LSM for different layers.

Simple soil
LSM  -  layer 1 (0.1 m)

LSM  -  layer 2 (0.3 m)

LSM  -  layer3 (0.6 m)

LSM  -  layer4 (1 m)

Figure 9. Predicted and observed soil moisture at Wind River Crane site.

5.2.4 PBL height and vertical profile
PBL heights on the three peak ozone days are plotted in Figure 10 for the time when daily peak values were reached.  The LSM-1 run generally predicted lower PBL heights along the west side of the Cascades, especially in western Washington.  For this part of the domain, the peak PBL heights from the LSM-1 run were around 800 to 1000 m.  In contrast, the simple soil-1 run predicted average peak heights around 1200 m in this area for all three days.  Different patterns showed up for the east side of the Cascades where the LSM-1 generally predicted higher PBL heights, except for the very low heights in the lower right corner of the domain associated with areas of convective rainfall.

Mixing heights estimated from upper air soundings at Salem, OR were compared to simulations from two models as shown in Figure 11.  The LSM-1 run predicted lower PBL heights on July 24, 25 and 27 than the simple soil-1 run. On July 26 and 28, the pattern was opposite. Compared to observed values (only available on July 26 to 28), both models tended to overestimate mixing heights by 200 to 300 m on these peak ozone days.

Figure 10. Predicted PBL heights by LSM and simple soil model for July 1998 episode

Figure 11. PBL predicted by simple soil and LSM compared with observed values for July 1998 episode.

Vertical profiles of temperature, wind speed, and wind direction were also compared with the upper air soundings at Salem at 17PDT on July 25 and July 26 as shown in Figure 12.  The LSM-1 run captured the vertical temperature profile fairly well on July 25, whereas the simple soil-1 run appeared to overestimate the temperature and predicted a deeper mixed layer than the soundings.  On July 26, both models matched the temperature profile well up to 700 m but predicted a deeper mixed layer than the observations.  For wind speed, the LSM-1 run underestimated wind speeds up to 600 m and the simple soil-1 run showed some overestimation up to 1500 m on July 25.  On July 26, both models underestimated wind speed.  For wind direction, both models had very good performance on July 25.  On July 26, the LSM-1 run showed better agreement with the observations below the boundary layer.

Figure 12. Observed and predicted vertical profiles of temperature, wind speed and wind direction from the simple soil-1 and LSM-1 runs.  ("old_run" refers to the simple soil-1 run, and "rerun" refers to the LSM-1 run)

5.2.5 MM5 statistical evaluation
The meteorological simulations were also evaluated using the mean bias and mean error for wind speed, direction, and temperature (Table 4).  Four Ecology network sites (Castle Rock, Woodland, BPA, and Mt.Zion) were selected as independent sites and withheld from observational nudging for surface winds.  The mean bias of temperature from the LSM-1 run was 1.4C, about 1C smaller than the bias from the simple soil-1 run.  The mean error of temperature was also smaller in the LSM-1 run compared to the simple soil-1 run (2.9C versus 3.2C). The mean bias and mean error of wind speed and wind direction from the LSM-1 run (ME = 1.5 m/s for WS; ME = 50 for WD) were both larger than those from the simple soil-1 run (ME = 1.2 m/s for WS; ME = 40 for WD).  This could be related to the underestimation of daytime surface winds and resulting error in the wind direction.  The statistics for wind direction and wind speed were calculated separately for stations used for observational nudging and those withheld from observational nudging; these results show that model performance was similar for these two groups of stations.  This might due to the relative low density of the surface stations available for observational nudging in the region.  Nevertheless, for the simple soil-1 run, the results for obs nudging stations had slightly smaller error (38) in wind direction compared with the results for withheld stations (47).

Table 4. MM5 performance statistics for July 1998 episode
                                     1998
                                      Run
                                    T_bias
                                    T_error
                                    Wd_bias
                                   Wd_error
                                    Ws_bias
                                   Ws_error

                                       C
                                       C

                                      m/s
                                      m/s
                                      TDO
                                     LSM-1
                                     0.75
                                     2.83
                                      6.5
                                     45.4
                                     -0.90
                                     1.57

                                 simple_soil_1
                                     2.28
                                     3.05
                                     -1.5
                                     28.9
                                     -0.50
                                     1.19
                                  Castle Rock
                                     LSM-1
                                     1.33
                                     2.88
                                     -2.3
                                     58.3
                                     0.63
                                     1.56

                                 simple_soil_1
                                     2.85
                                     3.37
                                     -12.1
                                     63.1
                                     1.01
                                     1.27
                                      KLS
                                     LSM-1
                                     1.26
                                     2.89
                                     -9.1
                                     34.3
                                     0.07
                                     1.32

                                 simple_soil_1
                                     2.85
                                     3.22
                                     -9.4
                                     25.4
                                     0.37
                                     1.16
                                   Woodland
                                     LSM-1
                                     1.89
                                     3.20
                                     -8.5
                                     20.2
                                     -1.60
                                     1.88

                                 simple_soil_1
                                     2.49
                                     3.23
                                     -0.2
                                     15.6
                                     -1.00
                                     1.46
                                      BPA
                                     LSM-1
                                     2.08
                                     3.10
                                     -9.2
                                     42.8
                                     0.62
                                     1.48

                                 simple_soil_1
                                     2.95
                                     3.39
                                     -3.3
                                     36.8
                                     1.02
                                     1.29
                                      VUO
                                     LSM-1
                                     1.64
                                     2.86
                                      2.1
                                     52.9
                                     -0.36
                                     1.28

                                 simple_soil_1
                                     2.50
                                     2.96
                                      3.4
                                     46.9
                                     0.10
                                     1.00
                                      PDX
                                     LSM-1
                                     0.83
                                     2.63
                                     -3.6
                                     46.8
                                     -0.55
                                     1.63

                                 simple_soil_1
                                     1.92
                                     2.64
                                      5.7
                                     36.0
                                     -0.46
                                     1.25
                                   Mt. Zion
                                     LSM-1
                                     0.97
                                     2.62
                                      6.8
                                     67.7
                                     -0.36
                                     1.18

                                 simple_soil_1
                                     2.45
                                     3.16
                                     10.7
                                     74.0
                                     0.13
                                     0.97
                                      HIO
                                     LSM-1
                                     1.57
                                     3.25
                                     -18.9
                                     52.3
                                     -0.87
                                     1.40

                                 simple_soil_1
                                     2.97
                                     3.58
                                     -26.6
                                     39.0
                                     -0.76
                                     1.01
                                      TTD
                                     LSM-1
                                     1.46
                                     2.71
                                      7.3
                                     75.1
                                     -0.74
                                     1.36

                                 simple_soil_1
                                     2.98
                                     3.27
                                     25.1
                                     54.6
                                     -0.56
                                     1.15
                                      UAO
                                     LSM-1
                                     1.27
                                     2.66
                                      0.8
                                     58.9
                                     -0.44
                                     1.62

                                 simple_soil_1
                                     2.85
                                     3.22
                                     -7.8
                                     36.9
                                     -0.23
                                     1.09

Table 4. Cont.
                                      SLE
                                     LSM-1
                                     1.65
                                     2.88
                                      1.7
                                     47.6
                                     0.04
                                     1.77

                                 simple_soil_1
                                     3.00
                                     3.37
                                      5.4
                                     35.2
                                     0.24
                                     1.15

                                    average
                                      Run
                                    T_bias
                                    T_error
                                    Wd_bias
                                   Wd_error
                                    Ws_bias
                                   Ws_error

                                       C
                                       C

                                      m/s
                                      m/s
                                 all stations
                                     LSM-1
                                     1.39
                                     2.88
                                     -2.19
                                     50.18
                                     -0.37
                                     1.50

                                 simple_soil_1
                                     2.68
                                     3.21
                                     -0.90
                                     41.03
                                     -0.05
                                     1.17

                               Withheld stations
                                     LSM-1
                                     1.57
                                     2.95
                                     -3.31
                                     47.23
                                     -0.18
                                     1.53

                                 simple_soil_1
                                     2.68
                                     3.29
                                     -1.23
                                     47.37
                                     0.29
                                     1.25

                                Nudged stations
                                     LSM-1
                                     1.31
                                     2.84
                                     -1.63
                                     51.66
                                     -0.47
                                     1.49

                                 simple_soil_1
                                     2.67
                                     3.16
                                     -0.73
                                     37.86
                                     -0.23
                                     1.13

5.2.6 LSM run compared with simple soil model run
The differences from LSM-1 and simple_soil_1 runs are summarized below:

 LSM showed better simulation of surface temperatures.
 LSM predicted generally lower PBL heights along the west side of the Cascades on the peak ozone days.
 LSM was able to predict temporally and spatially varied soil moisture field in response to precipitation and evapo-transpiration.
 The performance for winds were slightly degraded in the LSM run compared to the simple soil model run due to well known problem of the MRF PBL scheme.
 Ozone simulation was also improved with MM5 including the Noah LSM as shown in the CMAQ modeling section.

Therefore, LSM-1 run was selected for the MM5 simulation due its overall improved meteorological simulation and better ozone predictions.

5.3 Modeling results and evaluation (July 1997 episode)
Surface temperature contours from MM5/MCIP are shown in Figure 13.  Compared to the July 1998 episode in which extensive high temperatures existed, the surface temperatures in 1997 episode were considerably lower and in the range of 12-35C.  There was generally good agreement between the predicted and observed surface temperatures and cloud coverage at Portland and Salem as shown in Figure 15a and b.  At the KLS site (Figure 15c) located along the I-5 corridor in southwestern Washington, the LSM-1 run under-estimated daytime temperatures on most days.  Nevertheless, there was a fairly large over-estimation of the daytime temperatures on July 20.  The model also missed the overcast condition in that morning, which might explain the overestimate of temperature as well as ozone (shown in the ozone modeling section) around the area.  Overall, however, the LSM-1 performance appears to be better for the 1997 episode compared to 1998, especially for nighttime temperatures.

The surface wind patterns in the afternoon of July 20 are shown in Figure 14.  There were consistent northwesterly/westerly flows across western Washington and Oregon.  Some convergence close to Milwaukie was apparent between the northwesterly and southwesterly winds in the simulation, which might contribute to the high ozone levels there.  Surface time series of wind speed and wind direction are shown in Figure 16a-c.  The LSM-1 run performed relatively well for wind direction. Similar to the 1998 episode, underestimation of daytime wind speeds were also the case for 1997.

Modeled PBL heights were compared with observations at Salem as shown in Figure 17.  On three of the four days when data were available (July 15, 17, and 22), the LSM-1 run predicted PBL heights were very close to the observations.  On July 21, the PBL heights were overestimated by about 200 m.

The LSM-1 performance statistics for the July 1997 episode are summarized in Table 5.  Similar to the 1998 case, Ecology meteorological sites (Castle Rock, BPA, and Mt. Zion) were withheld from observational nudging of surface winds.  Compared with the withheld stations, the stations used for observational nudging had a smaller mean error in wind direction (37 versus 49), but slightly larger mean bias and error in wind speed.  Overall, the statistics for the 1997 episode were better than for 1998, with smaller mean error in temperature (2.1C versus 2.9C) and wind direction (40 versus 50).  It is also worth noting that in 1997 there was a negative temperature bias and positive temperature bias in 1998; this which might be due to the better simulations of nighttime temperature in the 1997 episode.

Figure 13. Surface temperature pattern from MM5 for 17:00 PDT on July 20, 1997.

Figure 14. Surface wind pattern from MM5 for 17:00 PDT on July 20, 1997.
Figure 15a. Surface temperature and cloud cover time series predicted by LSM compared with observations at Portland.

Figure 15b. Surface temperature and cloud cover time series predicted by LSM compared with observations at Salem.

Figure15c. Surface temperature and cloud cover time series predicted by LSM compared with observations at KLS.

Figure 16a. Surface wind speed and wind direction time series predicted by LSM compared with observations at Portland.

Figure 16b. Surface wind speed and wind direction time series predicted by LSM compared with observations at Salem.

Figure 16c. Surface wind speed and wind direction time series predicted by LSM compared with observations at KLS.

Figure 17. PBL predicted by LSM compared with observed values for July 1997 episode.

Table 5. MM5/MCIP performance statistics for July 1997 episode
                                     1997
                                      Run
                                    T_bias
                                    T_error
                                    Wd_bias
                                   Wd_error
                                    Ws_bias
                                   Ws_error

                                     C
                                     C
                                      
                                      
                                      m/s
                                      m/s
                                      TDO
                                     LSM-1
                                     -0.63
                                     1.74
                                     -9.1
                                     36.1
                                     -1.37
                                     1.74
                                  Castle Rock
                                     LSM-1
                                     -0.16
                                     1.93
                                      2.4
                                     54.4
                                     0.15
                                     1.25
                                      KLS
                                     LSM-1
                                     -1.02
                                     1.82
                                     -20.6
                                     36.4
                                     -0.37
                                     1.42
                                      BPA
                                     LSM-1
                                     0.32
                                     2.04
                                     -3.3
                                     29.7
                                     0.36
                                     1.35
                                      PDX
                                     LSM-1
                                     -1.49
                                     2.14
                                     -4.7
                                     29.8
                                     -1.26
                                     1.71
                                   Mt. Zion
                                     LSM-1
                                      N/A
                                      N/A
                                     -2.5
                                     63.1
                                     -0.11
                                     1.24
                                      DLS
                                     LSM-1
                                     -3.50
                                     3.67
                                     -1.7
                                     35.2
                                     -0.99
                                     2.16
                                      HIO
                                     LSM-1
                                     -1.42
                                     1.96
                                     -22.4
                                     32.2
                                     -0.29
                                     1.50
                                      TTD
                                     LSM-1
                                     -1.44
                                     2.33
                                     29.1
                                     41.3
                                     -0.93
                                     1.48
                                      UAO
                                     LSM-1
                                     -0.39
                                     1.56
                                     -1.4
                                     42.3
                                     -0.82
                                     1.51
                                      SLE
                                     LSM-1
                                     -0.32
                                     1.74
                                      6.3
                                     44.7
                                     -0.87
                                     1.66

                                    average
                                      Run
                                    T_bias
                                    T_error
                                    Wd_bias
                                   Wd_error
                                    Ws_bias
                                   Ws_error

                                     C
                                     C
                                      
                                      
                                      m/s
                                      m/s
                                 all stations
                                     LSM-1
                                     -1.01
                                     2.09
                                     -2.54
                                     40.49
                                     -0.59
                                     1.55
                               withheld stations
                                     LSM-1
                                     0.08
                                     1.98
                                     -1.15
                                     49.09
                                     0.13
                                     1.28
                                nudged stations
                                     LSM-1
                                     -1.28
                                     2.12
                                     -3.06
                                     37.26
                                     -0.86
                                     1.65

5.4 Back trajectory analysis
An analysis of back trajectories for the Portland urban area was conducted by Ecology using the MM5 wind fields (Bowman, personal communication) and the Vis5D software package.  This analysis was done at an early stage of the modeling work, and therefore, the simple soil-1 runs were used for both episodes.  On each day from July 26 to 29 in 1998 and July 18 to 21 in 1997, two 12-hr back trajectories starting 13 PDT and 17 PDT were produced for each monitoring site.  The trajectories terminated at 150 meters above the surface to avoid being kept in the surface layer.  The length of time a parcel spends along the path was accumulated if the parcel was within 500 meters of the surface.  This height was selected to accommodate seasonal and diurnal variations in the mixed layer.

Two summary plots with all available back trajectories for 1998 and 1997 are shown in Figure 18a and b.  The plots show that for both years the air parcels spent a relatively long time in the immediate area due to the low wind speeds that existed.  In 1998, most back trajectories originated from the north and northwest with a few exceptions coming from the southwest.  It appeared that there was no direct impact from the Puget Sound area in that year.  Compared to 1998, winds in 1997 were more varied.  In addition to trajectories from northwest/north and southwest, there were also trajectories that originated from the northeast in the Puget Sound region.

18a. Summary plots of back trajectories during July 26 to 29, 1998.

18b. Summary plots of back trajectories during July 18 to 21, 1997.

6 Photochemical air quality modeling

6.1 Modeling methods
EPA Models-3 Community Multi-scale Air Quality (CMAQ) Modeling System (Byun and Ching, 1999) version 4.3 was used for photochemical air quality modeling.  Based on state-of-science techniques, CMAQ is a multi-scale, multi-pollutant air quality model that simulates the transportation, transformation, and deposition of atmospheric pollutants including as photochemical precursors and oxidants, particulate matter, and airborne toxics.  It incorporates the output fields from the MM5/MCIP meteorological simulations and emissions derived from the Sparse Matrix Operator Kernel Emissions Modeling System (SMOKE) (http://cf.unc.edu/cep/empd/products/smoke/index.cfm), and then simulates the chemical transport using the CMAQ Chemical Transport Model (CCTM).

Initial and boundary conditions were primarily derived from GEOS-CHEM global model simulations (personal communication, Rob Elleman).  However, vertical ozone IC/BC concentrations were derived from a combination of data sources.  For the western boundary, ozone levels were based on Trinidad Head ozonesondes data collected during July 98 (personal communication, Dan Jaffe).  For the other three sides (north, east, and south), ozone concentrations were derived from ICTC global model simulations (personal communication, Youhua Tang).  The concentrations of each model species were height dependent.  The concentrations in the first model layer are shown in Table 6.  The CMAQ modeling domain is slightly smaller than the MM5 innermost domain with 99x99 horizontal grid cells at 4 km x 4 km spacing and with 22 layers in the vertical.  The SAPRC99 photochemical mechanism including aqueous chemistry but no aerosol dynamics was employed.  The aerosol module was not employed because of the lack of emission inventory data for key aerosol precursors.  The chemical speciation of the emission inventory was performed by SMOKE according to the SAPRC99 mechanism.  The Modified Euler Backward Interactive (MEBI) solver was used to solve the chemical kinetic equations.  The first two days of each episode were run twice as model spinup to minimize the effects of initial conditions.

     Table 6. Initial and boundary conditions for CMAQ run (first layer)
                                    Species
                                  Description
                                     East
                                     North
                                     South
                                     West

                                    (ppbV)
                                    (ppbV)
                                    (ppbV)
                                    (ppbV)
                                     HCHO
                                 Formaldehyde
                                   1.98E+00
                                   9.21E-01
                                   1.11E+00
                                   2.01E-01
                                      ALD
                       Acetaldehyde and higher aldehydes
                                   1.39E+00
                                   5.03E-01
                                   7.80E-01
                                   3.30E-02
                                      OP1
                           Methyl hydrogen peroxide
                                   6.03E-01
                                   5.45E-01
                                   7.43E-01
                                   8.22E-01
                                      KET
                                    Ketones
                                   7.51E+00
                                   4.52E+00
                                   4.69E+00
                                   1.92E+00
                                     ONIT
                                Organic nitrate
                                   2.69E-02
                                   1.96E-02
                                   1.23E-02
                                   2.07E-03
                                      ETH
                                    Ethane
                                   1.46E+00
                                   1.25E+00
                                   1.27E+00
                                   1.03E+00
                                      HC3
                 Alkanes w/ 2.7x10-13 > kOH < 3.4x10-12
                                   3.35E-01
                                   2.10E-01
                                   2.06E-01
                                   6.26E-02
                                      HC5
                 Alkanes w/ 3.4x10-12 > kOH < 6.8x10-12
                                   2.70E+00
                                   2.70E+00
                                   2.70E+00
                                   1.39E+00
                                      HC8
                         Alkanes w/ kOH > 6.8x10-12
                                   5.00E-01
                                   5.00E-01
                                   5.00E-01
                                   1.29E-01
                                      OL2
                                    Ethene
                                   5.00E-01
                                   5.00E-01
                                   5.00E-01
                                   1.50E-01
                                      OLT
                               Terminal olefins
                                   2.00E-01
                                   2.00E-01
                                   2.00E-01
                                   8.71E-02
                                      OLI
                               Internal olefins
                                   4.00E-01
                                   4.00E-01
                                   4.00E-01
                                   4.30E-02
                                      TOL
                      Toluene and less reactive aromatics
                                   4.00E-01
                                   4.00E-01
                                   4.00E-01
                                   2.14E-01
                                      XYL
                      Xylene and more reactive aromatics
                                   5.00E-01
                                   5.00E-01
                                   5.00E-01
                                   3.70E-01
                                      PAN
                     Peroxyacetyl nitrate and higher PANs
                                   1.55E-01
                                   1.20E-01
                                   5.89E-02
                                   3.24E-03
                                      ISO
                                   Isoprene
                                   4.00E+00
                                   1.46E+00
                                   3.08E+00
                                   2.06E-02
                                     MACR
                                 Methacrolein
                                   3.30E-01
                                   1.23E-01
                                   2.12E-01
                                   1.03E-03
                                      MVK
                              Methyl Vinyl Ketone
                                   3.82E-01
                                   1.61E-01
                                   2.31E-01
                                   1.38E-03
                                     MPAN
                     PAN analogue formed from Methacrolein
                                   5.83E-02
                                   3.71E-02
                                   2.67E-02
                                   2.67E-04
                                      NO2
                               Nitrogen dioxide
                                   5.67E-01
                                   5.09E-01
                                   1.90E-01
                                   1.17E-02
                                      NO
                                 Nitric oxide
                                   8.69E-02
                                   5.92E-02
                                   2.29E-02
                                   1.17E-03
                                      O3
                                     Ozone
                                   4.00E+01
                                   4.00E+01
                                   4.00E+01
                                   2.34E+01
                                     HNO3
                                  Nitric acid
                                   8.30E-01
                                   3.38E-01
                                   3.42E-01
                                   1.37E-02
                                     HNO4
                               Peroxynitric acid
                                   1.86E-03
                                   1.91E-03
                                   5.50E-04
                                   5.01E-05
                                      NO3
                               Nitrogen trioxide
                                   1.00E-01
                                   1.00E-01
                                   1.00E-01
                                   1.00E-01
                                     H2O2
                               Hydrogen peroxide
                                   2.35E+00
                                   1.26E+00
                                   1.55E+00
                                   9.37E-01
                                      CO
                                Carbon monoxide
                                   1.45E+02
                                   1.21E+02
                                   1.17E+02
                                   8.64E+01
                                     N2O5
                              Nitrogen pentoxide
                                   1.47E-03
                                   1.82E-03
                                   1.87E-04
                                   2.28E-05
                                      SO2
                                Sulfur dioxide
                                   5.00E-02
                                   5.00E-02
                                   5.00E-02
                                   3.00E-02
                                     SULF
                                 Sulfuric acid
                                   3.00E-01
                                   3.00E-01
                                   3.00E-01
                                   2.99E-01

6.2 CMAQ modeling results and evaluation (July 1998 episode)
The local ozone monitoring sites are shown in Figure 19.  Simulated surface ozone contours from the LSM-1 run for July 28 are shown in Figure 20 at hour 6, 10, 14, and 18 PDT.  At 6 PDT, nitric oxide (NO) titration effects were obvious within the urban core and along the I-5 corridor with ozone concentrations below 20 ppb.  At 10 PDT, ozone increases were evident south of Seattle with values above 60 ppb.  However, there was no evident ozone production downwind of Portland at that hour.  At 14 PDT, ozone values above 100 ppb were simulated immediately north and south of the Portland urban core.  Maximum ozone concentrations were simulated at 18 PDT, with the maximum predicted ozone concentration reaching 149 ppb south of Portland.

Figure 19. Ozone monitoring site map for Southwest Washington and Oregon.

Figure 20. Simulated surface ozone contour on July 28, 1998 at 6, 10, 14, and 18 PDT.

Observed and simulated 1-hr surface ozone concentration time series are shown in Figure 21. Note that the first two days (July 24 and 25) were used as model spinup, so the results are not included in the statistical evaluation.  All monitoring sites except Hockinson and Wishram are located along the I-5 corridor.  Extending from North to South, Castle Rock, Woodland, and Sauvie Island are rural sites situated north of Portland; Mt View and Milwaukie are two suburban sites, close to Vancouver and slightly southeast of downtown Portland respectively; Carus, another rural site, is located about 30 miles south of Portland at the foot of the mountains; and Turner, the most southern site within the domain, is close to Salem, OR.  Hockinson and Wishram are the two sites that are further away from I-5 and influenced heavily by complex terrain close to the west slope of the Cascade Mountains and along the east edge of the Columbia River Gorge, respectively.

At Castle Rock, Woodland, Sauvie Island, and Mt View, the maximum observed ozone concentrations were close to 100 ppb during July 26 to 28.  Nighttime ozone titration was obvious at Sauvie Island and Mt View with concentrations decreasing to near zero.  At these four sites, the model simulated the ozone peaks reasonably well, although sometimes the duration of elevated ozone in the simulations was longer than in the observations.

At Milwaukie, observation data were missing on July 27 and part of July 26 and 28.  The available data show an exceedance of the 1-hr standard on July 26 with maximum value of 124 ppb. (NAAQS 1-hr ozone = 120 ppb, 8-hr ozone = 80 ppb).  The LSM-1 run underestimated the peak ozone on July 26 and slightly overestimated it on July 28.  At Carus, a series of three exceedances of the 1-hr and 8-hr ozone standards occurred on July 26 through 28, with 1-hr peak values of 136, 133, and 137 ppb, respectively.  Nighttime ozone at Carus remained about 20 ppb because it was not affected by local NOx sources.  Compared to the observations, the LSM-1 run missed the maximum ozone on the July 26 but captured the peaks fairly well on the following two days.  The nighttime values were also well simulated, but the timing of the daytime peaks were slightly delayed in the simulations.  At Turner, there was very good agreement between the observed and simulated ozone concentrations although nighttime ozone was overestimated.

The model performance was different at the complex terrain sites of Wishram and Hockinson.  At Wishram, ozone values were moderate throughout the episode with maximum value of 77 ppb on July 27.  The LSM-1 run performed reasonably well at this site.  At Hockinson, moderately high ozone values (close to 100 ppb) were observed.  However, the LSM-1 run seemed unable to capture the ozone peaks from July 26 to 28.

Figure 21. Observed and simulated 1-hr surface ozone concentrations for July 1998 episode

6.2.1 CMAQ statistics evaluation
CMAQ model performance was evaluated by the following set of ozone statistics based on the simulations from July 26 to 28.
 Normalized bias and normalized gross error between observed and predicted 1-hr/8-hr ozone concentrations.  Data within a selected time window were used in evaluation (10-19 PDT for 1-hr and 14-23 PDT for 8-hr ozone; shown in Table 7).  These time windows were selected to encompass periods of elevated ozone.
 Normalized bias between observed and predicted 8-hr daily maxima using spatially paired means. (Shown in Table 8)
 Normalized bias between observed and predicted 8-hr daily maxima using all data pairs. (Shown in Table 9)
 Correlation coefficients and scatter plots of observed and predicted 8-hr daily maxima using spatially paired means. (Shown in Figure 22)
 Quantile-quantile plots of observed and predicted 8-hr daily maxima using (a) all data pairs (b) spatially paired means. (Shown in Figure 23a and 23b)

The normalized gross error is defined as:

and the normalized bias is defined as:

At Castle Rock, Woodland, and Sauvie Island, located upwind of Portland, the LSM-1 run had a positive bias especially at Woodland and Sauvie Island (1-hr NB of 24% and 28%, respectively).  This could be related to the fact that simulated ozone peaks are slightly broader than the observed ones.  For spatially paired means, the normalized bias between observed and predicted 8-hr daily maxima are all below 20% at these sites, which meets EPA suggested guidelines (EPA, 1999).  Nevertheless, if evaluated on a daily basis (as shown in Table 9), there was a larger positive bias especially on July 28.

Mt. View and Milwaukie are two urban sites within the Portland/Vancouver airshed.  At Mt. View, the normalized bias and gross error were reasonable (1-hr NB = 2%, 8-hr NB = 3%, 1-hr NE = 34%, 8-hr NE = 26%).  For 8-hr daily maxima, the bias between the observed and predicted is generally negative when evaluated at the exact grid point of the monitoring site.  However, when evaluated using the surrounding 5x5 matrix of grid cells, the bias becomes positive as a result of steep horizontal ozone gradients around the site.  Due to missing data at Milwaukie, no statistics were calculated for this site.

At Carus and Turner, downwind of Portland, observed ozone peaks were generally well simulated as shown in the bias between observed and predicted 8-hr daily maxima.  However, the timing of the ozone peaks were slightly shifted at Carus, and consequently, the gross error was moderately high (1-hr NE = 36% and 8-hr NE = 27%).

Hockinson and Wishram are two sites further away from the I-5 corridor and influenced heavily by complex terrain.  The performance statistics were fairly good at Wishram.  At Hockinson, performance was poor with large underprediction.  Nevertheless, there were also steep horizontal ozone gradients around Hockinson so that the predicted 8-hr maxima are considerably higher when evaluated with the surrounding 5x5 grids.

Table 7. Normalized bias and normalized gross error between observed and predicted 1-hr/8-hr ozone concentrations. (1-hr statistics are calculated within 10-19 PDT, and 8-hr statistics are calculated within 14-23 PDT on July 26, 27, and 28, 1998.)
                                     Site
                                    1-hr NB
                                    1-hr NE
                                    8-hr NB
                                    8-hr NE
                                  Castle Rock
                                      12%
                                      24%
                                      9%
                                      16%
                                   Woodland
                                      24%
                                      31%
                                      23%
                                      26%
                                 Sauvie Island
                                      28%
                                      36%
                                      24%
                                      27%
                                   Mt. View
                                      2%
                                      34%
                                      3%
                                      26%
                                   Milwaukie
                                      N/A
                                      N/A
                                      N/A
                                      N/A
                                     Carus
                                      4%
                                      36%
                                      2%
                                      27%
                                    Turner
                                      10%
                                      29%
                                      5%
                                      16%
                                    Wishram
                                      -6%
                                      13%
                                      -6%
                                      9%
                                   Hockinson
                                     -17%
                                      36%
                                     -15%
                                      28%
Note: Values higher than EPA suggested model performance goal are highlighted in red.

Table 8. Normalized bias between observed and predicted 8-hr daily maxima using spatially paired means. (based on 5x5 and 1x1 grids)
                                     site
                                   Ave obs
                                8-hr daily max
                                     (ppm)
                       Ave pre 8-hr daily max 1x1 (ppm)
                                   NB (1x1)
                       Ave pre 8-hr daily max 5x5 (ppm)
                                   NB (5x5)
                                  Castle Rock
                                     0.075
                                     0.079
                                      4%
                                     0.081
                                      8%
                                   Woodland
                                     0.071
                                     0.080
                                      13%
                                     0.082
                                      16%
                                 Sauvie Island
                                     0.071
                                     0.081
                                      14%
                                     0.083
                                      16%
                                   Mt. View
                                     0.075
                                     0.066
                                     -12%
                                     0.083
                                      11%
                                   Milwaukie
                                      N/A
                                     0.085
                                      N/A
                                     0.092
                                      N/A
                                     Carus
                                     0.101
                                     0.096
                                      -5%
                                     0.098
                                      -3%
                                    Turner
                                     0.084
                                     0.085
                                      0%
                                     0.088
                                      5%
                                    Wishram
                                     0.061
                                     0.056
                                      -9%
                                     0.057
                                      -7%
                                   Hockinson
                                     0.078
                                     0.059
                                     -24%
                                     0.069
                                     -12%

Note: 	"1x1"  -  data extracted from the exact grids.
      "5x5"  -  data extracted from the surrounding 5x5 grids.

Table 9. Normalized bias between observed and predicted 8-hr daily maxima using all data pairs. (based on 5x5 and 1x1 grids)
                                     Site
                                     Date
                              Obs 8-hr daily max
                                     (ppm)
                         Pre 8-hr daily max 1x1 (ppm)
                                   NB (1x1)
                         Pre 8-hr daily max 5x5 (ppm)
                                   NB (5x5)
                                  Castle Rock
                                    July 26
                                     0.077
                                     0.073
                                      -6%
                                     0.075
                                      -3%
                                  Castle Rock
                                    July 27
                                     0.077
                                     0.088
                                      14%
                                     0.091
                                      17%
                                  Castle Rock
                                    July 28
                                     0.072
                                     0.075
                                      5%
                                     0.079
                                      10%
                                   Woodland
                                    July 26
                                     0.069
                                     0.071
                                      2%
                                     0.073
                                      5%
                                   Woodland
                                    July 27
                                     0.089
                                     0.091
                                      2%
                                     0.091
                                      2%
                                   Woodland
                                    July 28
                                     0.054
                                     0.079
                                      47%
                                     0.083
                                      55%
                                 Sauvie_Island
                                    July 26
                                     0.074
                                     0.069
                                      -7%
                                     0.070
                                      -4%
                                 Sauvie_Island
                                    July 27
                                     0.078
                                     0.090
                                      15%
                                     0.090
                                      16%
                                 Sauvie_Island
                                    July 28
                                     0.063
                                     0.086
                                      37%
                                     0.087
                                      39%
                                    Mt_View
                                    July 26
                                     0.071
                                     0.060
                                     -15%
                                     0.076
                                      7%
                                    Mt_View
                                    July 27
                                     0.078
                                     0.064
                                     -17%
                                     0.086
                                      10%
                                    Mt_View
                                    July 28
                                     0.076
                                     0.072
                                      -5%
                                     0.088
                                      16%
                                   Milwaukie
                                    July 26
                                     N/A
                                     0.082
                                     N/A
                                     0.086
                                     N/A
                                   Milwaukie
                                    July 27
                                     N/A
                                     0.085
                                     N/A
                                     0.091
                                     N/A
                                   Milwaukie
                                    July 28
                                     N/A
                                     0.087
                                     N/A
                                     0.098
                                     N/A
                                     Carus
                                    July 26
                                     0.117
                                     0.088
                                     -25%
                                     0.090
                                     -23%
                                     Carus
                                    July 27
                                     0.088
                                     0.093
                                      5%
                                     0.097
                                      10%
                                     Carus
                                    July 28
                                     0.098
                                     0.107
                                      9%
                                     0.107
                                      9%
                                    Turner
                                    July 26
                                     0.076
                                     0.070
                                      -8%
                                     0.074
                                      -3%
                                    Turner
                                    July 27
                                     0.098
                                     0.095
                                      -3%
                                     0.101
                                      3%
                                    Turner
                                    July 28
                                     0.078
                                     0.089
                                      13%
                                     0.089
                                      14%
                                    Wishram
                                    July 26
                                     0.060
                                     0.054
                                     -10%
                                     0.055
                                      -8%
                                    Wishram
                                    July 27
                                     0.063
                                     0.054
                                     -14%
                                     0.056
                                     -11%
                                    Wishram
                                    July 28
                                     0.061
                                     0.058
                                      -4%
                                     0.059
                                      -2%
Table 9. cont.
                                   Hockinson
                                    July 26
                                     0.070
                                     0.054
                                     -23%
                                     0.062
                                     -12%
                                   Hockinson
                                    July 27
                                     0.083
                                     0.058
                                     -30%
                                     0.069
                                     -16%
                                   Hockinson
                                    July 28
                                     0.082
                                     0.066
                                     -19%
                                     0.075
                                      -8%

Note: 	"1x1"  -  data extracted from the exact grids.
      "5x5"  -  data extracted from the surrounding 5x5 grids.

A scatter diagram of average observed and simulated 8-hr daily maxima (paired in space) is shown in Figure 22.  When plotted with the surrounding 5x5 grid points, the LSM-1 run predicted the peak and the lowest concentrations fairly well with R[2] of 0.63, but there was some overprediction of the moderate values (70-80 ppb).  When looking at the exact grid cell, there was more scatter around the moderate ozone concentrations.

Quantile-Quantile plots (Figure 23a and 23b) are also plotted for the observed and simulated 8-hr daily maxima which compares the frequency distributions of the observed and predicted ozone concentrations.  The plots show generally good agreement between the observed and predicted concentration distributions, but there was some underperdiction of the peak ozone and overprediction of moderate ozone (80-90 ppb) when evaluated using the range of concentrations within the 5x5 surrounding grid points.  When looking the exact grid point, the bias was similar except for some additional underprediction for the moderate concentrations (around 70 ppb).

Figure 22.  Scatter plot of the average observed and predicted 8-hr daily maxima for 5x5 and 1x1 grids for July 1998 episode

Figure 23a. Quantile-Quantile plot of observed and predicted 8-hr daily maxima using all data pairs for 5x5 and 1x1 grids for July 1998 episode.

Figure 23b. Quantile-Quantile plot of observed and predicted 8-hr daily maxima using spatially paired means for 5x5 and 1x1 grids for July 1998 episode.

6.2.2 Comparisons with NOx/VOC monitoring data
In 1998, there were four NOx monitoring sites in southwest Washington and Oregon: Lafayette, Castle Rock, Woodland, and Mt. View.  In addition to the three sites mentioned previously, Lafayette is a suburban site very close to the Milwaukie ozone monitoring site.  A major roadway (US-26) is located about 100 m north of the Lafayette site.  Predicted and observed NO/NO2 from 6 to 21 PDT on each day (July 26-28) are shown in Figure 24 for each monitoring site.

At Lafayette, there were NO peaks in the morning associated with early morning emissions into a shallow mixed layer and lower NO concentrations during the remainder of the daylight hours.  The LSM-1 run appeared to underestimate the early morning peaks and slightly overestimated observed levels from noon into the afternoon.  NO2 concentrations were also generally high in the morning, and lower in the afternoon.  The model captured the trend of NO2 well at most times, especially on July 27.  At Woodland, early morning NO peaks were underestimated and predicted NO2 concentrations were also generally lower than the observed ones.  At Castle Rock, both NO and NO2 were quite low and there was a lack of a distinct diurnal pattern due to its rural location.  The LSM-1 run predicted NO well and also captured the range of NO2 values.  At Mt. View, another urban/suburban site, the LSM-1 run underpredicted morning peaks of NO on the first two days, and overpredicted on the last day. Concentrations of NO2 were also overestimated at this site, especially for the afternoon hours.  One thing worth noticing is that, the grid points of Mt. View and Lafayette both have fairly large NO emissions related to mobile sources, which might have a large impact on the predicted NO/NO2 concentrations.

VOC measurements were also collected at Lafayette on selected days in 1998.  The simulated and observed VOC concentrations are shown at Figure 25.  The VOC data were canister measurements with sampling time from 5-8 and 8-11 PDT on selected days.  The model values were converted from CMAQ output by summing of selected species (alkanes, aromatics, alkenes, terpenes, and isoprene).  The observed NMOC was mostly within 150-200 ppbC except for July 28 when value of 740 ppbC was reported. The LSM-1 run simulated VOC levels perfectly on July 27.  There was a slight underestimation on July 26. On July 28, the LSM-1 run missed the elevated level in the early morning and then slightly overestimated the total VOC concentration at 8-11 PDT.

Figure 24. Observed and simulated NO/NO2 concentrations at Lafayette, Woodland, Castle Rock, and Mt. View from July 26 to 28, 1998.

Figure 25. Simulated and observed VOC (ppmC) at Lafayette during the July 1998 episode.

6.3 CMAQ modeling results and evaluation (July 1997 episode)
Surface ozone contours from the LSM-1 run are shown in Figure 26a and 26b for the afternoon of July 19 and 20.  On July 19, elevated ozone concentrations were simulated downwind of Portland with maximum slightly above 100 ppb.  On the next day, high level ozone was simulated right around the Portland urban area with maximum close to 130 ppb.

Figure 26a. Simulated surface ozone contour on July 19, 1997 at 17PDT.

Figure 26b. Simulated surface ozone contour on July 20, 1997 at 17PDT.

Predicted and observed surface ozone time series were plotted in Figure 27 for each monitoring site.  At Castle Rock, Woodland, and Mt. View, ozone concentrations were quite low on most days except July 19 when moderate concentrations (around 60 ppb) occurred.  The LSM-1 run slightly overestimated ozone levels on July 19 and simulated most low ozone days well. Nevertheless, there was significant overestimation on July 20 at all three sites.  As mentioned in the meteorological modeling section, there were also underestimation of cloud cover and overestimation of surface temperatures on that day around these sites, which might explain the large overestimation of ozone.

At Mt. View and Milwaukie, moderate values occurred on July 19 at both sites and on July 20 at Mt. View.  The peak 1-hr average ozone reached 101 ppb at Milwaukie on July 20, which was the maximum observed in this episode.  The LSM-1 run simulated ozone quite well on low ozone days, and slightly overestimated on moderate and high days.  There also appeared to be some time delay of the ozone peaks at these two sites.

At Carus and Turner, ozone concentrations were around 80 ppb on July 19 and 20, and quite low on rest of the days.  The LSM-1 run showed some overestimation but captured the overall trend quite well on July 19 and 20.  On the low ozone days, both sites showed very good agreement between observations and simulations.

At Hockinson and Wishram, ozone levels were low to moderate throughout the episode.  The LSM-1 run simulated ozone quite well at Wishram.  At Hockinson, where simulation was poor in the 1998 episode, model performance was better.  It simulated the right level of ozone on July 20, although the timing of the peak was shifted.

Figure 27. Observed and simulated 1-hr surface ozone concentrations for July 1997 episode.

6.3.1 CMAQ statistics evaluation
Model performance was evaluated using the performance measures based on the simulations from July 17 to 21.  Normalized bias and normalized gross error between observed and predicted 1-hr and 8-hr ozone concentrations are shown in Table 10.  Normalized bias between observed and predicted 8-hr daily maxima using spatially paired means and all data pairs are shown in Table 11 and 12, respectively.

The three upwind sites, Castle Rock, Woodland, and Sauvie Island, all showed positive normalized bias around 20% due to the large overestimation of ozone on July 20.  Normalized bias between observed and predicted 8-hr daily maxima using spatially paired means was around 20% if evaluated at the exact grid, and 30% using the maxima from the 5x5 grids as shown in Table 11.

Mt. View and Milwaukie, the two urban sites, had a negative (1hr NB = -21%) and positive bias (1hr NB = 15 %), respectively.  The negative bias at Mt. View was mostly due to underprediction on low ozone days.  The two sites both had relatively large normalized errors, partly due to the timing shift of peaks.  On July 19 and 20, the normalized bias between the observed and predicted 8-hr daily maxima was about 20% if evaluated at the exact grid as shown in Table 12.

The run showed fairly good statistical performance at the Carus and Turner downwind sites (1-hr NB = 0% and -7%; 1-hr NE = 22% and 17%, respectively).  Normalized bias between observed and predicted 8-hr daily maxima using spatially paired means or all data pairs was also mostly below 20%.  Reasonably good performance was found at the Wishram and Hockinson sites.

Table 10. Normalized bias and normalized gross error between observed and predicted 1-hr/8-hr ozone concentrations. (1-hr statistics are calculated within 10-19 PDT, and 8-hr statistics are calculated within 14-23 PDT from July 17 to 21, 1997.)
                                     Site
                                    1-hr NB
                                    1-hr NE
                                    8-hr NB
                                    8-hr NE
                                  Castle Rock
                                      22%
                                      37%
                                      18%
                                      32%
                                   Woodland
                                      17%
                                      31%
                                      16%
                                      27%
                                 Sauvie Island
                                      22%
                                      31%
                                      20%
                                      27%
                                   Mt. View
                                     -21%
                                      43%
                                     -23%
                                      36%
                                   Milwaukie
                                      15%
                                      46%
                                      5%
                                      27%
                                     Carus
                                      0%
                                      22%
                                      -3%
                                      14%
                                    Turner
                                      -7%
                                      17%
                                      -8%
                                      12%
                                    Wishram
                                      -5%
                                      12%
                                      -5%
                                      9%
                                   Hockinson
                                      -3%
                                      25%
                                      -1%
                                      19%
Note: Values higher than EPA suggested model performance goal are highlighted in red.

Table 11. Normalized bias between observed and predicted 8-hr daily maxima using spatially paired means. (based on 5x5 and 1x1 grids)
                                     Site
                                   Ave obs
                                8-hr daily max
                                     (ppm)
                       Ave pre 8-hr daily max 1x1 (ppm)
                                   NB (1x1)
                       Ave pre 8-hr daily max 5x5 (ppm)
                                   NB (5x5)
                                  Castle Rock
                                     0.034
                                     0.040
                                      19%
                                     0.044
                                      32%
                                   Woodland
                                     0.036
                                     0.043
                                      20%
                                     0.045
                                      27%
                                 Sauvie Island
                                     0.036
                                     0.044
                                      24%
                                     0.046
                                      29%
                                   Mt. View
                                     0.040
                                     0.036
                                     -10%
                                     0.050
                                      26%
                                   Milwaukie
                                     0.038
                                     0.044
                                      15%
                                     0.050
                                      29%
                                     Carus
                                     0.045
                                     0.048
                                      6%
                                     0.054
                                      21%
                                    Turner
                                     0.047
                                     0.045
                                      -4%
                                     0.050
                                      7%
                                    Wishram
                                     0.046
                                     0.043
                                      -6%
                                     0.045
                                      -1%
                                   Hockinson
                                     0.042
                                     0.040
                                      -6%
                                     0.045
                                      6%
Note:	 "1x1"  -  data extracted from the exact grids.
       "5x5"  -  data extracted from the surrounding 5x5 grids

Table 12. Normalized bias between observed and predicted 8-hr daily maxima using all data pairs. (based on 5x5 and 1x1 grids)
                                     Site
                                     Date
                              Obs 8-hr daily max
                                     (ppm)
                         Pre 8-hr daily max 1x1 (ppm)
                                   NB (1x1)
                         Pre 8-hr daily max 5x5 (ppm)
                                   NB (5x5)
                                  Castle Rock
                                    July 17
                                     0.028
                                     0.021
                                     -26%
                                     0.023
                                     -16%
                                  Castle Rock
                                    July 18
                                     0.032
                                     0.036
                                      11%
                                     0.044
                                      35%
                                  Castle Rock
                                    July 19
                                     0.058
                                     0.064
                                      12%
                                     0.066
                                      15%
                                  Castle Rock
                                    July 20
                                     0.028
                                     0.056
                                      99%
                                     0.061
                                     114%
                                  Castle Rock
                                    July 21
                                     0.022
                                     0.024
                                      7%
                                     0.028
                                      25%
Table 12. Cont.
                                   Woodland
                                    July 17
                                     0.033
                                     0.025
                                     -24%
                                     0.026
                                     -20%
                                   Woodland
                                    July 18
                                     0.034
                                     0.033
                                      -4%
                                     0.037
                                      6%
                                   Woodland
                                    July 19
                                     0.053
                                     0.069
                                      29%
                                     0.069
                                      29%
                                   Woodland
                                    July 20
                                     0.032
                                     0.060
                                      85%
                                     0.067
                                     107%
                                   Woodland
                                    July 21
                                     0.026
                                     0.027
                                      5%
                                     0.028
                                      10%
                                 Sauvie_Island
                                    July 17
                                     0.029
                                     0.024
                                     -18%
                                     0.026
                                     -12%
                                 Sauvie_Island
                                    July 18
                                     0.033