Title: Outdoor Air Quality | EPA's Report on the Environment (ROE) | US EPA
Headings: Outdoor Air Quality
Report on the Environment
Outdoor Air Quality
What are the trends in outdoor air quality and their effects on human health and the environment?
Importance of Outdoor Air Quality
Anthropogenic Focus
Three Categories of Indicators
Pollutant Fate and Transport
Exposure to Outdoor Air Pollution
Other Considerations
ROE Indicators
References

Content: They vary widely from local to global in scale: Air pollution can be local. For instance, ambient concentrations of benzene tend to be greatest near major sources (e.g., oil refineries, chemical production facilities) and in high-traffic areas. Air pollution can also be regional or national in nature. For example, emissions sources hundreds of miles away can contribute to airborne fine particulate matter at a given location. 3
A few air pollution issues are global in nature, such as intercontinental transport of particles during dust storms. Stratospheric ozone depletion, also, is affected by releases of ozone-depleting substances from countries worldwide. Time: Temporal scales also vary among pollutants and typically reflect some combination of changes in emissions and fluctuations in weather. Ambient air concentrations of some air pollutants, like ground-level ozone, have considerable diurnal and seasonal variations.