Source characterization of major emission sources in the Imperial and Mexicali Valleys along the US/Mexico border

Abstract

Chemical profiles for particle emissions are needed for source apportionment studies using the chemical mass balance (CMB) receptor model. Source measurements of geological sources, motor vehicle exhaust, vegetative burning (e.g. asparagus, field burning, charbroil cooking), and industrial sources (e.g. oil-fueled glass plant, manure-fueled power plants) were acquired as part of the Imperial/Mexicali Valley Cross Border PM 10 Transport Study in 1992. Six different source sampling techniques (i.e. hot- and diluted-exhaust sampling, ground-based source sampling, particle sweeping/grab sampling, vacuum sampling, and laboratory resuspension sampling) were applied to acquire filter samples of PM 2.5 and PM 10 (particulate matter with aerodynamic diameters <2.5 and 10 μm, respectively). Filter samples were analyzed for mass by gravimetry, elements (Na to U) by X-ray fluorescence, anions (Cl −, NO 3 −, SO 4 =) by ion chromatography, ammonium (NH 4 +) by automated colorimetry, soluble sodium (Na +) and potassium (K +) by atomic absorption spectrophotometry, and organic and elemental carbon (OC, EC) by thermal/optical reflectance. Concentration data were acquired for a total of ∼50 chemical species. Elevated abundances of crustal components (Al, Si, K, Ca, Fe) from geological material, carbon (OC, EC) and trace elements (Br, Pb) from vehicle exhausts, carbon (OC, EC) and ions (K +, Cl −) from vegetative burning, ions (SO 4 =, NH 4 +, Na +, K +, Cl −) and elements (Cl, Se) from a manure-fueled power plants, and sulfur and trace elements (Na +, Pb, Se, Ni, V) from an oil-fueled glass plant were found in the resulting source profiles. Abundances of crustal species (e.g. Al, Si, Ca) in the Imperial/Mexicali Valley geological profiles are more than twice those found in central and southern California. Abundances of lead in motor vehicle exhausts indicate different vehicle fleets in border cities. Emission profiles from field burning and charbroil cooking specific to the border area show that a majority (>60%) of emissions are comprised of carbon, with high organic to total carbon ratios (0.93 to 0.97). Abundances of sulfate and ammonium account for nearly 60% of the manure-fueled power plant's emissions. Elevated levels of metals (Na +, Pb, Cd, Se) and byproducts of petroleum combustion (S, Ni, V) were found in the oil-fueled glass plant's emissions.