El Paso High Ozone August 11, 2008

• Ozone Animation
• Plume Animation
• Satellite Animation
• Satellite Image - Texas 1:00 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 Monday, August 11th.   The highest measured eight-hour average was 100 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 128 parts per billion (ppb) for the hour from 3:00 to 4:00 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 of 23 ppb at Ciudad Juarez 20-30 Club from 92 ppb at Noon to 115 ppb at 1:00 p.m. MDT.   AQI Level Red was measured at only one site, AQI Level Orange or higher was measured at eight 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 eleventh 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 four at Ivanhoe C414.

Skies were mostly cloudy in the early morning but became partly cloudy mid-day and then overcast in the late afternoon and evening as thundershowers developed in the mountains to the east.   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 southeast 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 small volume of air that stayed over the urban area.   The high temperature was 94 degrees Fahrenheit (°F) at the El Paso Intercontinental Airport.

Regional background levels of ozone, in the air coming into the El Paso area, ranged from about 55 to 56 ppb as indicated by the peak eight-hour averages at the Santa Teresa, La Union, and Solano sites in New Mexico.   The difference of 44 to 45 ppb between the measured eight-hour area maximum of 100 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 44 to 45 percent of the measured 100 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.