Meteorological and photochemical modeling of ozone and carbon monoxide episodes for the Paso Del Norte Airshed. Part II: Air quality modeling

Areas surrounding El Paso County, Texas and Ciudad Juarez, Mexico (the Paso Del Norte Region) fail to meet the National Ambient Air Quality Standards (NAAQS) for carbon monoxide (CO), and ozone (O3). In 1989, the United States and Mexico signed Annex V to the 1983 La Pax Agreement, thereby agreeing to jointly monitor, gather emissions information, and conduct air quality modeling of the area to determine which emission control strategies would most efficiently improve air quality in the Paso Del Norte region. To provide the data necessary to conduct reliable air quality modeling, EPA, TNRCC, and others conducted the Paso Del Norte Ozone Study (PDNOS) during the summers of 1996 and 1997.

Under EPA Region 6 sponsorship, the PDNOS data set was used to support advanced meteorological, emission, and air quality modeling of the entire Paso Del Norte region. Given the technically complex and nonlinear factors and processes that affect ozone and CO distributions in the region, an advanced photochemical air quality grid model, CAMx, was selected for evaluation, and application. CAMx inputs were developed using output from RAMS prognostic meteorological modeling and from extensive gridded emissions modeling. The RAMS modeling is described in a companion paper. CAMx was applied using a nested-grid configuration, with horizontal grid resolutions of 4-km, 2-km, and 1-km. The periods modeled included a three-day ozone episode during August 1996, and a one-day CO episode during December 1997. This paper describes both the CO and ozone CAMx applications for the Paso Del Norte region, including many of the technical obstacles that had to be addressed, and evaluates the ozone and carbon monoxide benefits due to automotive fuel changes.