Atmospheric removal processes for high molecular weight organochlorines

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Abstract
Factors influencing the atmospheric removal of polychlorinated biphenyls (PCB) and the chlorinated insecticides p,p′,‐DDT, chlordane, and toxaphene were investigated in the city of Columbia, South Carolina, and at the North Inlet estuary on the South Carolina coast. Dry deposition velocities (Vd) for individual organochlorines (OC) varied by 1–2 orders of magnitude from day to day, and in Columbia log Vd was correlated with average wind velocity. Higher Vd were observed for the less volatile OC, reflecting a greater degree of attachment to aerosols. Average Vd (cm/s) in Columbia were: Aroclor 1016 = ≤0.04, Aroclor 1254 = 0.43, chlordane = 0.068, and p,p′‐DDT = 1.3. The trend in Vd paralleled the percentages of these OC retained by a glass fiber filter during high volume air sampling. Vd for Aroclor 1254 and p,p′‐DDT at North Inlet were about 3–4 times lower than those in Columbia. Toxaphene was the most prevalent OC in precipitation at North Inlet, with concentrations exceeding 100 ng/1 during the late summer and early fall. Average washout ratios at North Inlet were: Aroclor 1254 = 94, p,p′‐DDT = 87, chlordane = 8.4, and toxaphene = 246. Dry and wet removal rates for Aroclor 1254 and p,p′‐DDT were more similar than might be expected from the large difference (more than 2 orders of magnitude) in their reported vapor pressures, although the vapor pressure for Aroclor 1254 is not accurately known. The similarity of PCB and p,p′‐DDT removal rates suggests an explanation for the fact that PCB and p,p′‐DDT ratios in seawater are about the same as those in the ocean atmosphere.