San Antonio High Ozone May 8, 2008

• Ozone Animation
• Plume Animation - Regional
• Satellite Animation
• Satellite Image - East Texas 2:34 pm - True Color (from UT CSR)
• Winds Aloft at Ledbetter (near La Grange)

High ozone was measured on the northwest side of the San Antonio area on Thursday, May 8th.   The highest measured eight-hour ozone average was 78 parts per billion (ppb) at the Fair Oaks Ranch Continuous Ambient Monitoring Station (CAMS) 502.   This measurement rated as Level Orange, Unhealthy for Sensitive Groups, on the U.S. Environmental Protection Agency (EPA) Air Quality Index (AQI) scale.   The highest one-hour ozone measurement was 91 ppb from 5:00 to 6:00 p.m Central Daylight Time (CDT) also at Fair Oaks Ranch CAMS 502.   Only two sites reached AQI Level Orange out of 10 sites reporting complete ozone data for the day.   Moderate or higher ozone levels were reported at eight sites. This was the first day this year with AQI Level Orange ozone measurements somewhere in the San Antonio area.   The U.S. Environmental Protection Agency lowered the 8-hour threshold for Level Orange from 85 ppb to 76 ppb this year.

Skies were clear to partly cloudy with light northerly winds in the morning, shifting to the east and southeast in the afternoon.   The high temperature reached 95 degrees Fahrenheit (°F) at the San Antonio Airport.

Regional background levels of ozone were at least about 58 to 61 ppb as indicated by peak eight-hour ozone measurements at Heritage Middle School C622, Seguin C506, and New Braunfels C504.   The difference of about 17 to 20 ppb between the measured eight-hour area maximum of 78 ppb and the approximate regional background level was likely caused by local air pollution sources in the San Antonio area.   The estimated local contribution was about 22 to 26 percent of the measured 78 ppb area eight-hour peak.

The Plume Animation - Regional shows the estimated plume tracks from large industrial sources of oxides of nitrogen (NOx) and/or volatile organic compounds (VOC), as well as plume tracks for the center of the broad urban plumes the larger cities in Central Texas.   The plume animation suggests that urban and industrial emissions from the San Antonio area were in the vicinity of the highest ozone measurements.