News & Events

2008 Ozone Season National Recap (

Tuesday, December 16, 2008


With cooler temperatures and fewer daylight hours, October marks the end of the ozone season for many areas of the country. Compared with last year, preliminary 2008 ozone data show widespread decreases in the number of days on which ozone levels reached Unhealthy for Sensitive Groups (USG) or above on the Air Quality Index (AQI) in cities east of the Rocky Mountains.

Overall, St. Louis, MO, showed the greatest fall in the number of USG days (from 35 days in 2007 to 6 days in 2008); this number was well-below the 10-year average of 34 days. Despite the general decrease in the East, Miami, FL, and Dallas-Fort Worth, TX, experienced more unhealthy days than last year, although neither exceeded their 10-year averages.

In the West, some cities showed an increase in the number of days reaching AQI levels of USG and above compared to last year, while others showed a decrease. The largest increase was in Sacramento where summer wildfires contributed to enhanced ground-level ozone formation.

An illustration of the 2008 national ozone season review is below. It displays the number of days on which ground-level ozone reached USG or above on the AQI from May through September in 2007 and 2008, compared with corresponding 10-year averages, adjusted to the new ozone standards.

Health Tip: Cut back on strenuous outdoor exercise when air quality is expected to be unhealthy. This is especially important for children, older adults, and other sensitive groups, such as people with heart or lung disease.

Click here for a comparative national map of days reaching the level of "Unhealthy for Sensitive Groups" (USG) or higher. Only 4 such days were called in the Lehigh Valley - Berks region this year.