Houston High Ozone September 30, 2008

• Ozone Animation
• Plume Animation
• Plume Animation - Regional
• Back Trajectory CAMS 620 3:00 pm CDT
• Back Trajectory CAMS 620 4:00 pm CDT
• Satellite Image - East Texas 3:46 am - False Color (from UT CSR)
• Satellite Image - East Texas 11:25 am - False Color (from UT CSR)
• Satellite Image - East Texas 3:03 pm - True Color (from UT CSR)
• Satellite Image - East Texas 3:07 pm - False Color (from UT CSR)
• Satellite Image True Color - Houston 11:55 am CDT (from UW SSEC)
• Satellite Image True Color - Houston 3:03 pm CDT (from UW SSEC)

High ozone was measured on the south side of the Houston metro area on Tuesday, September 30th.   The highest measured eight-hour average was 94 parts per billion (ppb) at the Texas City Continuous Ambient Monitoring Station (CAMS) 620 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 112 parts per billion (ppb) for the hour from 3:00 to 4:00 p.m. Central Daylight Time (CDT), also at Texas City CAMS 620.   Level Orange ozone was measured at 18 sites, with "Moderate" or higher ozone at all 39 sites reporting complete data for the day.   This day was the 31st day with Level Orange or higher ozone measurements, based on the new ozone standard and AQI.   It was the 12th day with measured levels exceeding the old 8-hour ozone standard.

Skies were clear all day. Winds were light from the north in the morning and increased from the northwest mid-day.   Along the immediate coast, winds shifted to the south to southeast with the seabreeze in the late afternoon.   The high temperature was 90 degrees Fahrenheit (°F) at George Bush Houston Intercontinental Airport, and 91°F at Hobby Airport.    The Galveston Airport weather station was still down after Hurricane Ike.

Regional background levels of ozone coming into the Houston area were around 64 to 74 ppb as indicated by the peak eight-hour averages at Conroe CAMS 78, Northwest Harris County CAMS 26, and Katy Park CAMS 559.   The difference of 20 to 30 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 21 to 32 percent of the measured 94 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.