U.S. Air Quality

Welcome to the 2008 Ozone Season!

The 2008 ozone season is in full swing today, with unhealthy ozone air quality in California. Currently there are Code Orange conditions in Sacramento, Los Angeles, and San Diego, and Code Red conditions in San Bernadino County. The image below on the left shows the current AQI for California with the MODIS Aqua true color image overlaid.

EPA recently lowered the national ozone standard, so this is a good time to review how ozone levels are reported and what the color codes mean. The table below on the right lists the ozone air quality color codes and their corresponding Air Quality Index (AQI) values, the ozone standard set in 1997, and the new 2008 ozone standard. The ozone standard is an 8-hour average, which reflects the fact that ozone's health effects are not only instantaneous, but they can also occur over a longer time period. The ozone 8-hour average is called a running average, which means it is calculated from the 8 highest consecutive 1-hour ozone measurements during the day. Ozone has a photochemical source, which is why ozone levels typically peak in the afternoon and early evening on sunny days during the months of May through September in the United States. As the 2008 ozone season progresses, keep the new ozone standard in mind. It may seem like air quality is worse in your area compared to recent years, but that's just because the standard is now lower. What would have been a high Code Yellow day last year is a Code Orange day this year. Air quality is actually improving nationwide, and the new ozone standard reflects EPA's efforts to protect public health.

The image below shows the nationwide air quality forecasts for Tuesday. Code Orange (Unhealthy for Sensitive Groups) ozone has been forecasted for several cities. Sensitive Groups include young children, senior citizens, and anyone with cardio-pulmonary diseases such as asthma. If you live in San Diego, Fresno, Las Vegas, Denver, Phoenix, or Mobile, keep an eye on the ozone levels tomorrow.