Air pollution in london. is it increasing or decreasing

this task is about the air pollution in London. we need information and statistics about air pollution in London from any sources but it should be trustful and create our own graph or chart which represent what we found from these statistics.Then and determine the air pollution increasing or decreasing.

i think the writing should include brief introduction about air pollution ,sources of pollution and effect and give example of it if its found.
any referencing ..

http://uk might be helpful