Houston High Ozone
September 20, 2004

• Ozone Animation
• Plume Animation - Houston
• Plume Animation - Southeast Texas
• Backward Air Trajectory
• Winds Aloft at Ellington Field
• Satellite Image - Texas 12:28 p.m. CDT True Color
  (from UW SSEC)
• Satellite Image - Houston 12:31 p.m. CDT True Color
  (from UT CSR)
• Satellite Image - Houston 2:20 p.m. CDT True Color
  (from UT CSR)
• Satellite Animation - GOES 12

High ozone was measured on the west side of the Houston area on Monday, September 20th. Moderate easterly winds pushed the high ozone as far west as the La Grange area. The highest measured one-hour ozone was 127 parts per billion (ppb) for the hour from 2:00 p.m. to 3:00 p.m. Central Daylight Time (CDT) at the Katy Park Continuous Ambient Monitoring Station (CAMS) 559. The highest eight-hour average of 93 ppb was measured at West Houston CAMS 554. The peak one-hour and eight-hour averages rated as Level Orange, Unhealthy for Sensitive Groups, on the U.S. Environmental Protection Agency (EPA) Air Quality Index (AQI) scale. Katy Park CAMS 559 was the only site to exceed the one-hour ozone standard out of 39 sites reporting ozone data for the day in the Houston metro area. Katy Park CAMS 559 and West Houston CAMS 554 were the only sites in the Houston area that measured Level Orange on the AQI scale. Fayette County CAMS 601 also measured Level Orange and it is likely that ozone reached Level Orange in a large area between Fayette and Harris Counties, but there is no confirmation because a lack of monitors in this area. This day was the 31st this year so far with measurements above the one-hour ozone standard in the Houston area and the 46th day so far this year with a Level Orange or higher AQI rating because of high ozone.

Fair weather prevailed with partly cloudy skies. Winds were moderate all day and shifted gradually from east-northeast in the morning to east-southeast and southeast in the afternoon. George Bush Houston Intercontinental Airport had a high temperature of 92 degrees Fahrenheit (°F) and Galveston Airport had a high of 88°F.

Regional background levels of ozone, in the air coming into the Houston area, were about 65 ppb as indicated by the peak one-hour averages at Seabrook CAMS 45 and Galveston Airport CAMS 34. The difference of 62 ppb between the measured one-hour area maximum of 127 ppb and the approximate peak regional background level of 65 ppb was likely caused by local air pollution sources in the Houston area. The estimated 62 ppb local contribution was 49 percent of the measured 127 ppb area one-hour peak.

The Plume Animation - Detailed Emissions shows the estimated plume tracks from large industrial sources of oxides of nitrogen (NOx) and volatile organic compounds (VOC), along with the plume tracks for the centers of the broad urban plumes coming from Downtown Houston and other major urban areas. The plume animation suggests that urban and industrial emissions from the Houston Ship Channel area were in the vicinity of the highest ozone measurements on the west side of Houston.

The Backward Air Trajectory shows the estimated path of the air that arrived at Fayette County CAMS 601 at the beginning of the peak ozone hour. The trajectory tracks the air at one-hour increments back to 1:00 a.m. CDT. The trajectory inidicates that the high ozone air mass probably passed across the Houston area earlier in the morning. The gray rings on the trajectory indicate the uncertainty of the trajectory positions based on one mile of uncertainty per hour of trajectory duration.