Government of Nova Scotia Government of Nova Scotia Nova Scotia, Canada




Acid Deposition
Acid deposition is the end product of reactions between sulphur oxides (SOx), nitrogen oxides (NOx) and water in the atmosphere. Acid deposition reaches the earth as precipitation (wet deposition: acid rain, fog, snow) and as gases, acid aerosols and particles (dry deposition or sedimentation).
Acidification is the process of changing into an acid or becoming more acidic (i.e., having lower pH). For example, acid rain causes soils and lakes to become more acidic.
Acid Rain
Acid rain forms when the pollutants sulphur dioxide (SO2) and nitrogen oxides (NOx) mix with water to form acids that fall as precipitation (fog, rain or snow). This is referred to as "wet deposition", a major component of acid deposition. Learn more about acid rain.
Air Quality and Health Advisory
An Air Quality and Health Advisory is a notice to the general public warning them that air quality will be poor. This allows people to plan their activities to reduce risk of exposure for themselves or those under their care. Also see Special Air Quality Statements
Air Quality Forecast
An air quality forecast is a prediction of what the air quality is likely to be over the next few days. It is similar to a weather forecast, and even needs to use the weather forecasts to make the prediction. Currently forecasting is only available for ozone, one of the components of smog. When poor air quality is predicted an Air Quality and Health Advisory will be issued.
Air Quality Index (AQI)
An air quality index is a simple scale that assigns numbers and values (good, fair, poor, very poor) based on the potential effects of the ambient (outdoor) concentration of air pollutants. Learn more about the AQI.
Ambient Air Quality
Ambient air quality is also known as outdoor air quality. It does not refer to indoor air quality or to emissions discharged from a source (such as a stack or a vehicle).
Ambient Monitoring
Ambient monitoring measures the concentrations of pollutants in outdoor air. Learn more about ambient monitoring in Nova Scotia.
The atmosphere is composed of 78% nitrogen (N2), 21% oxygen (O2), 0.9% argon (Ar), 0.03% carbon dioxide (CO2), and trace amounts of other gases.
Buffering Capacity
Buffering capacity is the ability of water and soil to resist changes in pH. Low levels of alkalinity in the water and soil in Nova Scotia mean the province has a low acid buffering capacity and is unable to neutralize acid precipitation.
Carbon Dioxide (CO2)
Carbon Dioxide is a colourless, odourless gas. CO2 is present in the atmosphere at 0.03% by volume. Since the Industrial Revolution, CO2 levels have increased by about 31%. CO2 is the most common greenhouse gas.
Carbon Monoxide (CO)
Carbon Monoxide is a poisonous, colourless, odourless and tasteless gas, generated through combustion processes.
Common Air Pollutants
Common air pollutants in ambient air include contaminants such as ground level ozone (O3), total particulate matter (TPM) (or total suspended particulate (TSP)), particulate matter less than or equal to 10 micrometres (PM10), particulate matter less than or equal to 2.5 micrometres (PM2.5), sulphur dioxide (SO2), nitrogen oxides (NOx), volatile organic compounds (VOCs) and carbon monoxide (CO). Some common air pollutants are emitted directly, while others like O3 may be formed through chemical reactions of precursor (primary) air pollutants.
Criteria Air Contaminants (CAC)
Criteria Air Contaminants are key primary air pollutants emitted directly from a number of sources (including industrial production, fuel combustion, transportation vehicles, incineration, dust from paved and unpaved roads, forest fires, etc.) that contribute to air pollution and affect human health. In Canada, according to the Canadian Environmental Protection Act (CEPA), CAC include total particulate matter (TPM) (or total suspended particulate (TSP)), particulate matter less than or equal to 10 micrometres (PM10), particulate matter less than or equal to 2.5 micrometres (PM2.5), sulphur dioxide (SO2), oxides of nitrogen (expressed as NO2), volatile organic compounds (VOCs) and carbon monoxide (CO). Pollutants defined as CACs may differ among countries and jurisdictions.
Critical Load
Critical load is the amount of deposition that an ecosystem can accept before long-term harmful effects occur. The critical load threshold for acid deposition to lakes in Nova Scotia is 8 kilograms of sulphate per hectare per year (kg/ha/y) based on wet deposition only. New critical load estimates for sulphur (S) and nitrogen (N) for both wet and dry deposition are being developed based on recent scientific studies.
Fine Particulate Matter (PM2.5)
Fine particulate matter, also called PM2.5, is made up of very small particles that are less than 2.5 micrometres in diameter (one micrometre is 1/1000 of a millimetre). These particles can find their way past our natural defences (nose hair and mucus) and end up deep in our lungs.
Fossil Fuels
Fossil fuels are formed from the remains of ancient plant and animal life and include coal, oil, natural gas and their derivatives.
Greenhouse Gases (GHG)
Greenhouse gases are chemical compounds in the earth's atmosphere that trap heat in the earth's atmosphere by absorbing infrared energy radiated off the earth's surface and reflecting it back to the earth's surface. Greenhouse gases include carbon dioxide (CO2), methane (CH4), nitrous oxides (N2O), halocarbons [chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs)] and sulfur hexafluoride (SF6).
Halocarbons are chemicals that contain carbon plus chlorine, fluorine or bromine. Halocarbons can be toxic at very high levels. Halocarbons include chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs). They are created by human activities and act like greenhouse gases.
Haze occurs when small particles in ambient air reduce visibility.
Hydrogen Sulphide (H2S)
Hydrogen Sulphide is a colourless gas that smells like rotten eggs at low concentrations. At high concentrations H2S is odourless and highly poisonous.
Lead (Pb)
Lead is a toxic, soft, malleable, dense metallic element.
Mercury (Hg)
Mercury is a silvery metallic element that is present naturally in the environment but is also released by human activity. High concentrations of mercury can be toxic to humans.
Methane (CH4)
Methane is a colourless, odourless gas. CH4 is a greenhouse gas.
Neutralize means to create a neutral solution (with a pH of 7) by adding acid to reduce alkalinity, or by adding alkali (ie., liming) to reduce acidity. Acid precipitation can be neutralized if there is enough alkalinity in the water or soil. See Buffering Capacity
Nitric Oxide (NO)
Nitric Oxide is a gas that combines with oxygen in the atmosphere to form nitrogen dioxide (NO2).
Nitrogen Dioxide (NO2)
Nitrogen Dioxide is a reddish-brown poisonous gas produced when nitric oxide combines with oxygen.
Nitrogen Oxides (NOx)
Nitrogen Oxides include the gases nitric oxide (NO) and nitrogen dioxide (NO2). In the presence of sunlight, NOx react with volatile organic compounds (VOCs) to form the smog component ozone (O3). NOx can also combine with ammonia to form secondary particulates.
Nitrous Oxide (N2O)
Nitrous Oxide is a colourless, sweet-tasting gas, composed of two nitrogen molecules and one oxygen molecule. N2O is a powerful greenhouse gas.
Ozone (O3)
Ozone is a compound made up of three atoms of oxygen bonded together. In the upper atmosphere (stratosphere), naturally occurring ozone protects us from harmful ultraviolet rays (see Stratospheric Ozone Layer). In the lower atmosphere ground-level ozone can damage our lungs and vegetation (see Smog). Pollutant emissions destroy stratospheric ozone and make more ground-level ozone.
Ozone-Depleting Substances (ODS)
Ozone-depleting substances are chemicals manufactured by humans which have all the following characteristics: they contain chlorine or bromine, they are gases when not under pressure, and when released at earth's surface, they are stable enough to be transported into the earth's stratosphere before they start to break down. When ODS break down, chlorine and bromine help to accelerate the natural destruction of ozone molecules and the thinning, or 'depleting', of the ozone layer. CFCs, which are used in refrigeration, foams and solvents, as well as halons, which are used to suppress fires, are among the most potent ozone-depleting substances (ODS). Other ODS include HCFCs, carbon tetrachloride, methyl bromide, and methyl chloroform. Countries around the world are working to eliminate the production and use of ODS in an effort to protect the ozone layer.
Ozone Layer
See Stratospheric Ozone Layer
Particulates or Particulate Matter
See Total Suspended Particulate or Fine Particulate Matter.
pH is a scale from 0 to 14 used to describe the acidity or alkalinity of a solution. A pH of 7 is neutral. A pH below 7 has increasing acidity and a pH above 7 has increasing alkalinity.
Polluter pays principle
The polluter pays principle is the belief that those who pollute should pay for the costs they impose on society.
Smog is used to describe the mixture of pollutants in the air that we breathe. The main contributors to smog in Nova Scotia are ground level ozone and fine particulate matter.
Smog Advisory
See Air Quality and Health Advisory
Smog Forecast
See Air Quality Forecast
Special Air Quality Statements
Special Air Quality Statements are issued to the general public when unusual large-scale air quality related events (such as smoke from large forest fires) are forecast or are already in progress in the region.
Stratospheric Ozone Layer
The stratospheric ozone layer is located within the stratosphere, 15 to 35 kilometres above the earth's surface, with the greatest concentration of ozone at about 25 kilometres. 90% of the ozone (O3) in the earth's atmosphere is concentrated in the 'ozone layer.' In the ozone layer, ozone is constantly being created and destroyed by natural processes. The ozone layer protects the earth by acting as a filter for ultraviolet (UV) radiation from the sun and reducing the amount of harmful UV reaching the earth's surface. Certain synthetic chemicals accelerate the destruction of ozone, causing the ozone layer to become thinner (see Ozone-Depleting Substances) and allowing more harmful UV to reach the earth.
Sulphate is a salt of sulphuric acid.
Sulphate Deposition
See Acid Deposition
Sulphur Dioxide (SO2)
Sulphur Dioxide (SO2) is a colourless, poisonous gas. It is the major precursor to acid rain in Nova Scotia..
Total Particulate Matter (TPM)
See Total Suspended Particulate
Total Suspended Particulate (TSP)
Total Suspended Particulate (TSP) refers to particles in the air such as smoke, soot, dust and aerosols that remain suspended and do not settle out easily. TSP includes particles with a diameter less than 100 micrometres in diameter (one micrometre is 1/1000 of a millimetre).
Volatile Organic Compounds (VOCs)
VOCs are substances that produce vapours at normal temperatures. VOCs can react with nitrogen oxides (NOx) in the presence of sunlight to form ground-level ozone, a major component of smog.