Ken Larsen's web site - Air Quality
As the world's human population rises, air pollution will rise and global warming will follow.
A measure of air quality has been invented called the Air Quality Index (AQI). [definition]
The AQI is based on measurements of these five outdoor air pollutants:
Carbon monoxide
Nitrogen dioxide
Ozone
Particulate matter
Sulfur dioxide
Current AQI's in various U.S. locations: