Contributions of regional transport and local sources to ozoneexceedances in Houston and Dallas: Comparison of results from aphotochemical grid model to aircraft and surface measurements

摘要

During the 2000 Texas Air Quality Study (TexAQS) and 2006 Texas Air QualityStudy (TexAQS II) field experiments, aircraft measured ozone concentrations upwind,across, and downwind of the Houston and Dallas urban areas. Background ozonetransported into Houston contributed, on average, approximately 50% and 66% of the totalozone on 8-h ozone exceedance days investigated by aircraft flights during TexAQS andTexAQS II, respectively. Analysis of a flight over Dallas on one exceedance day showedthat transported ozone constituted 72% of the total ozone concentration. The aircraftmeasurements show that these two major metropolitan areas can be brought close toexceeding the 1997 8-h National Ambient Air Quality Standard for ozone of 0.08 ppmsolely by the ozone contribution of regional transport before additional contribution fromlocal sources. Large local contributions were also observed, particularly in Houston.Transport contributions to Dallas area ozone were quantified using the Comprehensive AirQuality Model with Extensions (CAMx) photochemical grid model and sourceapportionment methods. Model-predicted ozone concentrations were compared to ozonemeasurements from the aircraft and the surface monitoring network, and showedagreement on the importance of regional transport and local ozone formation. Theseresults emphasize the benefits of regional control strategies, and suggest that local controlsalone may not be sufficient to ensure attainment of the 8-h ozone standard in Houston andDallas.