Where does ground-level ozone come from?
Ground-level ozone is formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs), such as xylene, react in the atmosphere in the presence of sunlight. NOx and VOCs are called ozone precursors. Motor vehicle exhaust, industrial emissions, and chemical solvents are the major sources of these chemicals. Ozone pollution is a concern during the summer months when the weather conditions needed to form it – lots of sun, hot temperatures – normally occur. Although these precursors often originate in urban areas, winds can carry NOx hundreds of miles, causing ozone formation to occur in less populated regions as well. For information about how you can reduce your contribution to the ozone problem, please visit http://www.epa.gov/air/actions/.
