San Antonio High Ozone September 26, 2008

• Ozone Animation
• Plume Animation - Regional
• Backward Air Trajectory CAMS 501
• Backward Air Trajectory CAMS 23
• Satellite Image - Texas 11:15 am - False Color (from JHU APL)
• Satellite Image - Texas 12:13 pm - True Color (from UW SSEC)
• Satellite Image - East Texas 1:09 pm - False Color (from UT CSR)
• Winds Aloft at Ledbetter (near La Grange)
• Winds Aloft Mid-Day at Ledbetter (near La Grange)

High ozone was measured on the west and southwest side of the San Antonio area on Friday, September 26th.   The highest measured eight-hour ozone average was 84 parts per billion (ppb) at the Elm Creek Continuous Ambient Monitoring Station (CAMS) 501.   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 87 ppb from 3:00 to 4:00 p.m. and again from 4:00 p.m. to 5:00 p.m. Central Daylight Time (CDT) also at Elm Creek CAMS 501.   Only two sites reached AQI Level Orange and exceeded the new ozone standard out of 10 sites reporting complete ozone data for the day in the San Antonio area. Moderate or higher ozone levels were reported at all 10 sites.    This was the fourth 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.    There have been no exceedances of the old 8-hour standard in San Antonio so far this year.

Skies were clear to partly cloudy with light northwest winds in the morning and northeast winds in the afternoon.    The high temperature reached 88 degrees Fahrenheit (°F) at the San Antonio Airport.

Regional background levels of ozone were about 66 to 73 ppb as indicated by peak eight-hour ozone measurements at Calaveras CAMS 59 and Seguin CAMS 506.   The difference of about 11 to 18 ppb between the measured eight-hour area maximum of 84 ppb and the approximate regional background level was likely caused by local air pollution sources.   The estimated local contribution was about 13 to 21 percent of the measured 84 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.