Dallas-Fort Worth High Ozone May 20, 2008

• Ozone Animation
• Plume Animation
• Backward Trajectory - Cleburne C77 6 pm
• Backward Trajectory - Cleburne C77 7 pm
• Satellite Animation
• Satellite Image - Dallas Fort Worth 11:31 am - True Color (from UT CSR)
• Satellite Image - East Texas 11:31 am - True Color (from UT CSR)
• Satellite Image - Texas 2:47 pm - True Color (from UW SSEC)

High ozone was measured on the southwest side of the Dallas-Fort Worth area on Tuesday, May 20th.   The highest measured eight-hour ozone average was 93 parts per billion (ppb) at the Cleburne Airport Continuous Ambient Monitoring Station (CAMS) 77.   This measurement 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 107 ppb from 6:00 to 7:00 p.m Central Daylight Time (CDT) also at Cleburne Airport CAMS 77.   Only one site reached AQI Level Orange and exceeded the eight-hour ozone standard, out of 19 sites reporting complete ozone data for the day.   Moderate or higher ozone levels were reported at 15 sites.   This was the third day this year with AQI Level Orange measurements somewhere in the Dallas-Fort Worth area based on the new ozone standard and the first day with measurements exceeding the old ozone standard.

Skies were partly cloudy with light southerly winds in the early morning, then shifting to the west and northwest and increasing in the late morning with a cold frontal passage and then turning to the northeast in the afternoon and evening.   This mid-day wind flow reversal helped to accumulate more air pollution in the same air mass.   The high temperature reached 94 degrees Fahrenheit (°F) at the Dallas-Fort Worth Airport, 91°F at Dallas Love Field, and 92°F at Fort Worth Meacham Field.

Regional background levels of ozone ranged from about 52 to 72 ppb as indicated by peak eight-hour ozone measurements at Parker County C76, Pilot Point C1032, and Greenville C1006.   The difference of about 21 to 41 ppb between the measured eight-hour area maximum of 93 ppb and the approximate regional background level was likely caused by local air pollution sources in the Dallas-Fort Worth area.   The estimated local contribution was about 23 to 44 percent of the measured 93 ppb area eight-hour peak.

The Plume Animation 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 coming from Downtown Dallas, Downtown Fort Worth, and other major urban centers.   The plume animation suggests that urban and industrial emissions from the Dallas area were in the vicinity of the highest ozone measurements.