1 Source Impact Quantification of Anthropogenic and Biogenic Emissions on Regional Ozone in the Mexico-U.S. Border Area using Direct Sensitivity Analysis 99-560 Alberto Mendoza-Dominguez, James G. Wilkinson, Yueh-Jiun Yang and Armistead G. Russell School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332 ABSTRACT Transboundary air pollution between the United States and Mexico has received increased attention since the late „70s. The Mexico-United States border area provides the opportunity to investigate ozone air pollution at urban and rural scales in the presence of very different anthropogenic and biogenic emission characteristics. In order to elucidate the impact of control strategies to reduce air pollution levels, an understanding of pollutant transport across the border is necessary, as well as a characterization of major anthropogenic and biogenic emission sources of ozone precursors. A previous air quality modeling study of the border area lacked a biogenic emissions inventory. In this study, an episodic biogenic hydrocarbon and nitric oxide emission inventory was developed for the Mexico-U.S. border area using GIS data and the Biogenic Emissions Inventory System (BEIS2). Then, the evolution of air pollutants was simulated using an Eulerian photochemical airshed model with the emission inventory accounting for both anthropogenic and biogenic emissions. Ground-level ozone was compared with a previous simulation that only incorporated anthropogenic emissions. Ozone levels increased throughout the domain, especially in the urban areas. Model performance, in general, improved against the run without biogenics, though results were biased towards ozone overprediction. The sensitivity of the ozone field to biogenic and anthropogenic emissions was calculated using a decoupled direct method for three dimensional air quality models (DDM-3D). DDM-3D revealed NO x - inhibited and VOC-limited areas. Finally, DDM-3D was used to analyze quantitatively the impact of different emission sources on ground-level ozone at urban and rural scales. INTRODUCTION Ground level ozone pollution has proven to be difficult to abate in American 1,2 and Mexican cities. 3 In particular, the Mexico-U.S. border presents the challenge of specifying control strategies in a region with high spatial variability of anthropogenic and biogenic emissions. Inside the border strip (100 kilometers to each side of the international limit), 14 twin cities comprise the bulk of the economic and industrial activity and each pair shares a common airshed. 4 Outside the strip, large metropolitan areas can affect the air quality of the border due to long range transport. A proper characterization of anthropogenic and biogenic emissions is necessary to further understand the transport and impact of pollutants across the border.