El Paso High Ozone September 4, 2008

• Ozone Animation
• Plume Animation
• Back Trajectory Ascarate Park C37
• Back Trajectory Delphi C663
• Satellite Animation
• Satellite Image - Texas 1:30 pm MDT - True Color (from UW SSEC)
• Winds Aloft at UTEP CAMS 12
• Winds Aloft at UTEP CAMS 12 Mid-day

High ozone was measured in the El Paso - Ciudad Juarez area on Thursday, September 4th. The highest measured eight-hour average was 115 parts per billion (ppb) at the Ciudad Juarez Delphi Continuous Ambient Monitoring Station (CAMS) 663 on the southeast side of Ciudad Juarez 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 137 parts per billion (ppb) for the hour from 4:00 to 5:00 p.m. Mountain Daylight Time (MDT) also at Juarez Delphi CAMS 663. The very rapid ozone increase mid-day hints that local emissions of highly reactive volatile organic compounds (HRVOC) may have been involved. The earliest sign of high ozone was the rapid increase to over 80 ppb at all three Ciudad Juarez sites by Noon MDT. AQI Level Red was measured at only one site, AQI Level Orange or higher was measured at seven sites, and AQI "Moderate" or higher ozone was measured at 10 of the 14 sites reporting complete ozone data for the day. This day was the 12th day this year with Level Orange ozone measurements somewhere in the El Paso - Ciudad Juarez area. The greatest number of days exceeding the new ozone standard at any site in El Paso County so far this year is five at Ivanhoe C414. Ozone measurements exceeding the old ozone standard have been measured on five days so far this year, with no more than two days at any site in El Paso County.

Skies were clear in the early morning and clear to partly cloudy mid-day. Winds were light from the southeast in the early morning but shifted to the west and northwest on the west side of the area causing a convergence into the central portion of the area. The high temperature was 88 degrees Fahrenheit (°F) at the El Paso Intercontinental Airport. The relatively cool high temperature is another indication that HRVOC emissions may have been an important factor.

Regional background levels of ozone, in the air coming into the El Paso area, ranged from about 50 to 57 ppb as indicated by the peak eight-hour averages at the Santa Teresa, La Union, and Chaparral sites in New Mexico. The difference of 58 to 65 ppb between the measured eight-hour area maximum and the approximate regional background level was likely caused by local air pollution sources in the El Paso area. This approximate local contribution was about 50 to 57 percent of the measured 115 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 El Paso and Ciudad Juarez urban centers. The plume animation suggests that urban and industrial emissions from the central El Paso - Ciudad Juarez area were in the vicinity of the highest ozone measurements. The backward trajectories for the peak ozone hours at Ascarate Park CAMS 37 and Delphi C663 suggest that the sources contributing to the highest ozone were in Mexico.