The Dry Deposition Gradient of Particle-associated Trace Metals Near a Freeway in Los Angeles

Jeong-Hee Lim¹, Keith D. Stolzenbach¹, Lisa D. Sabin² and Kenneth Schiff²

¹University of California, Los Angeles, Department of Civil and Environmental Engineering, Los Angeles, CA, 90095

²Lisa D. Sabin and Kenneth Schiff, Southern California Coastal Water Research Project, 7171 Fenwick Lane, Westminster, CA 92683

Abstract

Dry atmospheric deposition represents a potentially large source of trace metal contamination in urban stormwater runoff, yet there is a limited amount of research on the relationship between atmospheric emissions and water quality problems in urban areas.  In Los Angeles, which has among the worst air quality in the nation, significant quantities of toxic materials are released into the atmosphere every day, and paved road dust represents the largest source of particle-associated trace metal emissions to the atmosphere.  In order to better understand the role of roadways as a source of localized trace metal deposition, we characterized the horizontal dry deposition pattern of chromium, copper, nickel, lead and zinc upwind and at increasing distances downwind of the I-405 Freeway in coastal Los Angeles.  Dry deposition fluxes and atmospheric concentrations of these metals were highest at the site closest to the freeway, and reduced to approximately urban background concentrations within 450 m or less downwind of the freeway.  Compared with urban background, atmospheric particle size distributions indicated the freeway was a significant source of trace metals on large particles > 6 µm in diameter, which deposit close to their source and account for the increased dry deposition flux rates observed near the freeway.