Particle/Gas Concentrations and Distributions of PAHs in the Atmosphere of Southern Chesapeake Bay

Abstract

Atmospheric PAH concentrations were measured at four sites characterized as rural (Haven Beach), semi-urban (York River), urban (Hampton), and industrialized (Elizabeth River) areas as part of a study to quantify gaseous exchange fluxes across the air−water interface of southern Chesapeake Bay. Aerosol particle-associated PAH concentrations were similar at all sites; however, PAH gas-phase concentra tions in the urban areas were as much as a factor of 50 greater than those at the rural site. Mean total PAH concentrations (∑ 14 PAHs) ranged from 5.31 ng/m3 at the rural site to 71.6 ng/m3 at the urban site. Daily total PAH concentrations ranged from 1.23 to 180 ng/m3. Exponential increases in gaseous PAH concentrations with temperature were observed at the non-rural sites, suggesting volatilization from contaminated surfaces (soils, vegetation, roads) during warmer weather; whereas PAH gas concentrations at the rural Haven Beach site exhibited little seasonal variability. Aerosol particle-associated PAH levels were similar at all sites and increased in winter most likely due to the temperature dependence of particle-gas partitioning, including the cold condensation of gases to background aerosols as air masses are dispersed from source areas to remote regions, and increased sources from combustion of fossil fuel and wood for home heating. Plots of log Kp vs log pL° indicate PAH partitioning is not at equilibrium or that different distribution processes are operative in rural areas of southern Chesapeake Bay. In addition, plots of log Kp vs 1/T for individual PAHs demonstrate that different particle characteristics influence particle−gas distributions at the urban and rural sites.