A preliminary look at source-receptor relationships in the Texas-Mexico border area

Several factors have recently caused visibility impairment at Big Bend Nati onal Park, TX, to be of interest. Analyses of historical data collected the re have shown that visibility is poorer and fine particle concentrations ar e higher at Big Bend than at other monitored Class I areas in the western U nited States. In addition, air masses frequently arrive there after crossin g Mexico, where emissions are not well known. During September and October 1996, a field study was undertaken to begin examining the aerosol, visibili ty, and meteorology on both sides of the border. Results indicate that, dur ing the study, the largest fractions of fine mass and light extinction at B ig Bend were due to sulfates and the trace elements most closely associated with sulfate particles were Na and Se. Based on back trajectory modeling a nd the spatial, temporal, and inter-species relationships in the fine parti cle concentrations measured during the study, sulfates arrived at the park from both Mexico and the United States. Se was higher in Texas than in Nort hern Mexico, while V, Pb, Zn, Ni, and Mn were on average much higher in Mex ico.