PW02 Atmospheric Chemistry
Exhibit Hall
8:00 AM - Wednesday
(PW022) Dry Atmospheric Deposition of Trace Metals in the Los Angeles Region.
Schiff, K1, Sabin, L1, Stolzenbach, K2, Lim, J2, 1 So Cal Coastal Water Research, Westminster, CA, USA2 University of California Los Angeles, Los Angeles, CA, USA
ABSTRACT- Emissions of trace metals to the atmosphere and subsequent deposition, either directly to the waterbody surface or indirectly to the watershed for wash off during rain events, may contribute to the contamination observed in surface waters throughout the urban Los Angeles region. The goal of this study was to provide empirical data on atmospheric concentrations of trace metals on coarse particles and to estimate the direct and indirect mass loading of these trace metals due to dry atmospheric deposition in coastal watersheds of the Los Angeles Air Basin. To achieve this goal, atmospheric concentrations of chromium, copper, lead, nickel and zinc were measured seasonally using a Noll Rotary Sampler at six urban and one nonurban site throughout the Los Angeles coastal air basin. Dry deposition fluxes were calculated by summing the product of air concentration and theoretical deposition velocities of four coarse particle fractions (6-11, 11-20, 20-29, and >29 
m). Mean fluxes at urban sites ranged from 3.2 to 9.1, 11 to 34, 3.8 to 8.8, 8.3 to 29, and 69 to 228 g/m2/day for chromium, copper, nickel, lead and zinc, respectively. Mean fluxes at the urban sites were significantly higher than the nonurban site. Antecedent rainfall was a dominant factor affecting atmospheric concentrations and estimated fluxes; trace metal concentrations at the urban sites were similar to the nonurban sites when they were sampled within five days of measured precipitation. Comparisons for the Los Angeles River indicated direct dry atmospheric deposition produced a relatively small load of trace metals to that waterbody. In contrast, indirect dry deposition was potentially a very large source of trace metals to watershed loadings based on comparisons to load estimates from stormwater runoff.
Key words: trace metal, atmospheric deposition, Los Angeles, dry deposition