El Paso High Ozone July 14, 2008

• Ozone Animation
• Plume Animation
• Satellite Animation
• Satellite Image - Texas 1:54 pm MDT - True Color (from UW SSEC)
• Winds Aloft at UTEP CAMS 12
• Winds Aloft at UTEP CAMS 12 Mid-day
• Long Range Backward Trajectory - Delphi C663 2 pm MDT

Description
High ozone was measured in the El Paso - Ciudad Juarez area on Monday, July 14th.   The highest measured eight-hour average was 87 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 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 145 parts per billion (ppb) for the hour from 2:00 to 3:00 p.m. Mountain Daylight Time (MDT) also at Juarez Delphi CAMS 663. AQI Level Orange was measured at five 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 fourth day this year with Level Orange ozone measurements somewhere in the El Paso - Ciudad Juarez area.

Skies were mostly cloudy in the early morning but cleared by late morning.   A few clouds developed along the Franklin and Juarez mountains in the afternoon and distant thundershowers developed in the mountains well to the north through west through south of El Paso area in the afternoon and evening.   Winds were light from the southeast in the early morning but shifted to the northwest causing a flow reversal in the late morning, became light and variable in the early afternoon, and then increased and shifted to the southwest in the late afternoon.   The flow reversal in the late morning and the very light winds mid-day helped to accumulate local emissions in a smaller volume of air that stayed over the urban area.   The high temperature was only 89 degrees Fahrenheit (°F) at the El Paso Intercontinental Airport, and along with the early rapid ozone formation, hints that local emissions of highly reactive volatile organic compounds (HRVOC) may have been involved.

Regional background levels of ozone, in the air coming into the El Paso area, ranged from about 56 to 59 ppb as indicated by the peak eight-hour averages at Santa Teresa, La Union, and Desert View sites in New Mexico.   The difference of 28 to 31 ppb between the measured eight-hour area maximum of 87 ppb 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 32 to 36 percent of the measured 87 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.