Atmospheric deposition of toxic pollutants to the Great Lakes as measured by the Integrated Atmospheric Deposition Network

To determine atmospheric deposition of anthropogenic contaminants to the Great Lakes, the United States and Canada established the Integrated Atmospheric Deposition Network (IADN), designed to collect regional data representative of the air over the lakes. In this paper, we present an update of atmospheric loadings to the Great Lakes for seven organochlorine pesticides, four polychlorinated biphenyl (PCB) congeners and total-PCBs, four polycyclic aromatic hydrocarbons (PAHs), and four trace metals. Calculations are based on gas, particle, and precipitation samples obtained in 1993 and 1994 at the five master IADN sampling stations. Air-water exchange is the dominant process for most organochlorines and lower molecular weight PAHs. Within the uncertainty in the data given here, current atmospheric loadings are indistinguishable from air-water equilibrium having been achieved over the lakes. In other words, the deposition of most organochlorine compounds into the Great Lakes is about balanced by the evaporation of these compounds from the lakes. Uncertainties in gas-transfer loadings are due to our inexact knowledge of physiochemical parameters, averaging of data over long time scales, and insufficient data for nonatmospheric sources.