Houston High Ozone September 4, 2008

• Ozone Animation
• Plume Animation - Regional
• Satellite Animation
• Satellite Image True Color - Houston 2:30 pm CDT (from UW SSEC)
• Winds Aloft at La Porte
• Winds Aloft at La Porte Mid-Day

High ozone was measured in the Houston area on Thursday, September 4th. The highest measured eight-hour average was 103 parts per billion (ppb) at the Galveston Airport Continuous Ambient Monitoring Station (CAMS) 1034 and rated as Level Red, Unhealthy, on the U.S. Environmental Protection Agency (EPA) Air Quality Index (AQI) scale. The highest measured one-hour average was 117 parts per billion (ppb) for the hour from 6:00 to 7:00 p.m. Central Daylight Time (CDT), also at Galveston Airport CAMS 1034. Level Red ozone was measured only at one site and Level Orange ozone was measured at two sites, with "Moderate" or higher ozone at six sites out of 38 sites reporting complete data for the day. This day was the fifth day this year with Level Red ozone measurements somewhere in the Houston area and the 21st day with Level Orange or higher ozone measurements, based on the new ozone standard and AQI. It was the ninth day with measured levels exceeding the old 8-hour ozone standard.

Skies were mostly clear all day. Winds were light to moderate from the northwest in the morning and then shifted to the southeast in the afternoon along the coast with the seabreeze. The high temperature was 91 degrees Fahrenheit (°F) at George Bush Houston Intercontinental Airport, 90°F at Hobby Airport, and 89°F at Galveston Airport.

Regional background levels of ozone coming into the Houston area were around 42 to 44 ppb as indicated by the peak eight-hour averages at Katy Park CAMS 559, Northwest Harris County CAMS 26, and Conroe CAMS 78. The difference of 59 to 61 ppb between the measured eight-hour area maximum and the approximate regional background level was likely caused by local air pollution sources in the Houston area. The approximate local contribution was about 57 to 59 percent of the measured 103 ppb area eight-hour peak.

The Plume Animation 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 centers. The plume animation suggests that urban and industrial emissions from the Houston Ship Channel area were in the vicinity of some of the highest ozone measurements.