Central Texas High Ozone June 23, 2008

• Plume Animation - Regional
• Backward Air Trajectory CAMS 502
• Backward Air Trajectory CAMS 3
• Satellite Animation
• Satellite Image - Texas 2:35 pm - True Color (from UW SSEC)
• Satellite Image - Central Texas 2:35 pm - True Color (from UW SSEC)
• 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 and on the north and northwest side of the Austin area on Monday, June 23rd.   The highest measured eight-hour ozone average was 78 parts per billion (ppb) at the Fair Oaks Ranch Continuous Ambient Monitoring Station (CAMS) 502 on the northwest side of the San Antonio area and also at Austin Northwest (Murchison) CAMS 3.   These measurements 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 2:00 to 3:00 p.m. Central Daylight Time (CDT) also at Fair Oaks Ranch CAMS 502.   In the Austin area, the highest measured one-hour ozone average was 87 ppb at Round Rock CAMS 674 from Noon to 1:00 p.m. CDT. Only two sites reached AQI Level Orange out of 19 sites reporting complete ozone data for the day in Central Texas.   Moderate or higher ozone levels were reported at 15 sites. This was the second day this year with AQI Level Orange ozone measurements somewhere in the San Antonio area and the first in the Austin 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 partly cloudy with light and variable winds in the morning and southeasterly winds in the afternoon.   The high temperature reached 98 degrees Fahrenheit (°F) at the San Antonio Airport, 98 °F at Austin Bergstrom Airport, and 100°F at Austin Camp Mabry.

In the San Antonio area, regional background levels of ozone were about 59 to 62 ppb as indicated by peak eight-hour ozone measurements at Calaveras CAMS 59, Heritage Middle School CAMS 622, Seguin CAMS 506, and New Braunfels CAMS 504.   In the Austin area, the ozone background level was about 63 to 68 ppb upwind as indicated by San Marcos CAMS 675 and McKinney Roughs CAMS 684.   In the San Antonio area, the difference of about 16 to 19 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 Austin area, the difference of about 10 to 15 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 contributions were about 21 to 24 percent of the measured 78 ppb area eight-hour peak for the San Antonio area and about 13 to 19 percent of the measured 78 ppb area eight-hour peak for the Austin area.

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 and Austin areas were in the vicinity of the highest ozone measurements.