Air Quality Animation
August 06, 2002
Today's picture is an animated map of ground level ozone concentrations as they changed throughout the day on August 4, 2002. Ozone, a colorless gas whose molecules are made of 3 oxygen atoms, is a necessary part of the high-altitude stratosphere - it blocks ultraviolet light that can cause skin cancer. But ozone in the air we breathe here at ground level is bad - it is the main component of smog and can irritate and damage the respiratory system. Green in the maps above depicts areas with healthful air having low ozone concentrations. As the day progresses, yellow regions of air with higher ozone concentrations appear and may impact unusually sensitive people. By mid to late afternoon, several regions of the country are experiencing ozone levels that are unhealthy for sensitive groups, such as people with asthma or respiratory problems, depicted as orange on the map. Ground level ozone is a product of the chemical reaction of pollutants such as automobile exhaust in the presence of sunlight. Although ozone is often formed in urban and industrial areas, air circulation patterns can transport the toxic gas hundreds of miles from its point of origin. As the sun drops to the horizon, ground ozone levels naturally decrease. The US Environmental Protection Agency maintains a network of air quality monitoring stations across much of the country (except for the states colored gray above) and produces real time maps and forecasts of air quality and health risks.