San Antonio High Ozone September 6, 2008

• Ozone Animation
• Plume Animation - Regional
• Backward Air Trajectory CAMS 23
• Satellite Animation
• Satellite Image - Texas 2:14 pm - True Color (from UW SSEC)
• Satellite Image - Central Texas 2:14 pm - True Color (from UW SSEC)
• Satellite Image - East Texas 2:17 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 northwest side of the San Antonio area on Saturday, September 6th.   The highest measured eight-hour ozone average was 78 parts per billion (ppb) at the San Antonio Northwest Continuous Ambient Monitoring Station (CAMS) 23.   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 90 ppb from 4:00 to 5:00 p.m. Central Daylight Time (CDT) also at San Antonio Northwest CAMS 23.   Only one site reached AQI Level Orange and exceeded the new ozone standard out of 11 sites reporting complete ozone data for the day in Central Texas. Moderate or higher ozone levels were reported at 10 sites.    This was the third 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 partly cloudy with light and variable winds in the morning and southeasterly winds in the afternoon.   The high temperature reached 91 degrees Fahrenheit (°F) at the San Antonio Airport.

Regional background levels of ozone were about 60 to 62 ppb as indicated by peak eight-hour ozone measurements at Calaveras CAMS 59 and Seguin CAMS 506.   The difference of about 16 to 18 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.   The estimated local contribution was about 21 to 23 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.