Atmospheric deposition of organic contaminants to the chesapeake bay: Fid-Bau Portal

Atmospheric deposition of organic contaminants to the chesapeake bay

Leister, Dianne L. / Baker, Joel E.

Abstract To estimate loadings of contaminants from the atmosphere to the Chesapeake Bay, ambient atmospheric concentrations and wet deposition fluxes of several polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were measured at a shore-based station between June 1990 and December 1991. Geometric mean concentrations of individual PAHs in air ranged from 0.003 (dibenz[ah]anthracene) to 1.4 ng m⁻³ (phenanthrene) and the observed temporal variability in PAH levels in the air ranged from 0.1 to 41 % about the respective geometric mean concentrations. The mean ambient atmospheric PCB concentration over the Chesapeake Bay during the study period was 0.21 ng m⁻³, with a relative standard deviation of 56%. PCB concentrations in the air were slightly correlated with air temperature. Volume-weighted mean (VWM) concentrations of individual PAHs in precipitation ranged from 1.1 (dibenz[ah]anthracene) to 17 ng ℓ⁻¹ (pyrene). The VWM t-PCB concentration was 1.6 ng ℓ⁻¹. The temporal variability of HOC concentrations in rainfall was as large as one order of magnitude, with no apparent seasonal trend, suggesting highly variable HOC scavenging processes. Assuming a dry deposition velocity of 0.49±0.23 cm s⁻¹ dry particle fluxes of PAHs ranged from 1±0.4 (anthracene) to 16±7 (fluoranthene) μg m⁻² yr⁻¹. The dry deposition velocity was derived using monthly average wind speeds and temperature differentials derived for the Chesapeake Bay area from climatological compilations [Quinn T. L., Ondov J. M. and Holland J. Z. (1992) Dependence of deposition velocity on the frequency of meteorological observations for the Chesapeake Bay. J. Aerosol Sci. 23, S973–S976; Wu Z. Y., Ondov J. M., Holland J. Z. and Lin Z. C. (1992) Dry deposition fluxes of elements in Chesapeake Bay aerosol. J. Aerosol Sci. 23, 5969–5972]. Wet fluxes of PAHS ranged from 1 (anthracene) to 20 (pyrene) μg m⁻² yr⁻¹. Total (wet + dry) fluxes ranged from 2±0.4 (anthracene) to 35±7 (pyrene) μg m⁻² yr⁻¹. The t-PCB wet flux was 1.9 μg m⁻² yr⁻¹, with the estimated dry particle flux accounting for 75% of the total flux (3.3 ± 0.6 μg m⁻² yr⁻¹). The t-PCB wet flux in Chesapeake Bay is similar to that of rural Minnesota [2 μg m⁻² yr⁻¹. Franz T. P., Eisenreich S. J. and Swanson M. B. (1991) Evaluation of precipitation samplers for assessing atmospheric fluxes of trace organic contaminants. Chemo 23, 343–361]. Annual atmospheric loadings of individual PAHs to the surface waters of the Chesapeake Bay were calculated by extrapolating the total flux to the surface area of the Chesapeake Bay. Individual PAH loadings range from 23±5 (anthracene) to 403±81 (pyrene) kg yr⁻¹. and the t-PCB annual atmospheric loading is 38±7 kg yr⁻¹.