WARNING:Many of the articles in these links have a particular bias. Try to read several articles, look for the facts and then think about your own opinion on these matters.
Encyclopedia of the Atmospheric Environmentexcellent information on acid rain, ozone layer, etc.
Case studyThe effect of Chicago sewage and agricultural chemicals on the Illinois River.
UK Environment Agencythe Environment Agency provides both facts and figures on a wide range of pollution topics.
UK Air Quality Archivethis site has tons of data and information on air pollution, including real-time data. Choose a location and see how bad pollution is in your area - scary stuff!
Oil Pollutionoil pollution case studies including Exxon Valdez and Sea Empress