Houston High Ozone July 1, 2008

• Ozone Animation
• Plume Animation
• Plume Animation - Regional
• Backward Air Trajectory Park Place C416 2 pm
• Backward Air Trajectory Bayland Park C53 3 pm
• Backward Air Trajectory Bayland Park C53 4 pm
• Backward Air Trajectory Westhollow C410 4 pm
• Backward Air Trajectory Westhollow C410 5 pm
• Backward Air Trajectory Katy Park C559 5 pm
• Backward Air Trajectory Katy Park C559 6 pm
• Satellite Animation
• Satellite Image True Color - Texas 12:10 pm CDT (from UW SSEC)
• Satellite Image True Color - Houston 12:10 pm CDT (from UW SSEC)
• Winds Aloft at La Porte
• Winds Aloft at La Porte Mid-Day

Description
High ozone was measured mainly on the south, southwest, and west side of the Houston area on Tuesday, July 1st.   The highest measured eight-hour average was 83 parts per billion (ppb) at the Katy Park Continuous Ambient Monitoring Station (CAMS) 559 and rated as Level Orange, Unhealthy for Sensitive Groups, on the U.S. Environmental Protection Agency (EPA) Air Quality Index (AQI) scale.   The highest measured one-hour average was 125 parts per billion (ppb) for the hour from 5:00 to 6:00 p.m. Central Daylight Time (CDT), also at Katy Park CAMS 559. Level Orange ozone was measured at 10 sites, with "Moderate" or higher ozone at 38 sites out of 41 sites reporting complete data for the day.   This day was the 12th day this year with Level Orange or higher ozone measurements somewhere in the Houston area, based on the new ozone standard.    It was the fourth day with measured levels exceeding the old 8-hour ozone standard.

Skies were broken to overcast with high level cirrus clouds in the morning and partly cloudy with low level cumulus clouds in the afternoon and early evening.   Winds were light from the northeast in the early morning and then shifted to the east mid-day and then to the southeast in the afternoon with the bay breeze and seabreeze.   The high temperature was 92 degrees Fahrenheit (°F) at George Bush Houston Intercontinental Airport, 89°F at Hobby Airport, and 90°F at Galveston Airport.

Regional background levels of ozone coming into the Houston area were around 55 to 65 ppb as indicated by the peak eight-hour averages at Lake Jackson CAMS 1016, Galveston Airport CAMS 1034, Crosby CAMS 553, Kingwood CAMS 555, and Conroe CAMS 78.   The difference of 18 to 28 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 22 to 34 percent of the measured 83 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.   The backward air trjectories indicate that the air with the highest ozone peaks for the day had earlier passed across the central Ship Channel area.