This page contains links to U.S., state, and provincial sites containing some form of current air quality or ozone figures.
Some sites also have forecasts.
These substances in the presence of heat and sunlight react to form ozone. Ground-level ozone forms readily in the atmosphere, usually during hot weather. NOx is emitted from motor vehicles, power plants and other sources of combustion. VOCs are emitted from a variety of sources, including motor vehicles, chemical plants, refineries, factories, consumer and commercial products, and other industrial sources. Changing weather patterns contribute to yearly differences in ozone concentrations from city to city.