Source Apportionment of PM2.5 Measured in South Texas Near U.S.A. – Mexico Border

The implementation of the North American Free Trade Agreement (NAFTA) has increased industrial activities in urban areas along the U.S.-Mexico border. Brownsville, Texas is one such area that is currently in attainment of the National Ambient Air Quality Standards (NAAQS) for PM2.5 as set by the United States Environmental Protection Agency (U.S. EPA). However, the annual average PM2.5 concentrations measured were higher than those recorded at other cities of South Texas with greater industrial activity, including Corpus Christi and San Antonio. Thus, EPA PMF 5.0 was applied to apportion sources contributing to PM2.5 concentrations measured in this region from 2010 through 2013. An optimal solution of 10 sources was apportioned, with sea salt sulfates (19%) and non-sea salt sulfates (18%) being the major contributors. Other sources apportioned by PMF included sea salt (14%), biomass burning (13%), crustal dust (13%), road dust (3%), traffic emissions (7%), diesel emissions (3%), industrial emissions (6%), and secondary nitrates (5%). Anthropogenic emissions from on-road and off-road traffic from nearby highways, international bridge, and local marina were identified as major local contributors. Contribution of marine aerosols and coastal erosion was also observed. In addition to local sources, the impact of long-range transport across the U.S.-Mexico border was concluded to be the significant contributor for sources including non-sea salt sulfates, biomass burning, diesel engine emissions, and crustal dust.