Trans-boundary pollutant impacts of emissions in the Imperial Valley-Calexico region and from Southern California

Abstract

The western part of the border between Mexico and the United States consists of two primary regions, Tijuana-San Diego and Mexicali-Calexico (Imperial Valley). Over the last fifteen years Mexicali has been one of the fastest-growing cities in Mexico in terms of industrial development, job creation, and energy demand, thus resulting in increased air pollution and environmental degradation. This air pollution has thus been linked to high rates of asthma and respiratory diseases on both sides of the border. This thesis focuses on pollutant formation and pollutant interactions between the three regions of the Mexicali-Imperial Valley (MC), Tijuana-San Diego (TS), and Los Angeles (LA) areas. The MODELS-3 modeling approach is used for analyzing the formation of secondary species, and transport of both primary and secondary pollutants between the regions during three pollution episodes in July 2001, August 2001, and January 2002. Area and mobile sources are identified as primary pollutant emitters in MC and TS regions. Source contribution from within the region and from other regions is conducted using CMAQ/ DDM. During the summer episode, O3 plumes originating from TS are transported eastwards along the border region towards MC. O3 plumes generated from precursors emitted by LA mobile sources are transported towards MC and add up to 10 ppbv in the MC region. O3 plumes reach the border regions of California-Arizona and O3 concentrations up to 4 ppbv in the Grand Canyon area can be attributed to area sources in the MC region. Contribution of up to 11 ppbv of O3 in Calexico-Mexicali can be attributed to the high density of vehicles in and around the San Diego region. During the winter episode, the winds being southeasterly (towards southeast) plumes from TS, LA and Las Vegas unite and move towards the MC region with impacts of 10-35 μg m-3. The soil dust contributions from LA, TS and MC range between 5-25 μg m-3. MC area sources contribute a maximum of 34 μg m-3 PM2.5.