Measurements of NO2, HNO3, and PAN, as well as O3 were made in March 1985 at Alert, N.W.T., Canada. The observations show that PAN is by far the dominant NOy species at this Northern location at the onset of spring. Surface loss of HNO3 and possibly O3 seemed to occur over the snowy surface, but no loss of PAN was apparent. The observations are further evidence for the importance of PAN as a major carrier of the oxides of nitrogen in the clean troposphere. Although concurrently measured light hydrocarbons would appear to be sufficient for local formation of PAN, it is suggested that this did not take place but rather that long range transport from more southerly regions was responsible for the observed PAN levels.
Multiple regression was used to examine the temperature dependence and to elucidate temporal trends of atmospheric gas-phase partial pressures of 10 organochlorine pesticides at five sites near the Great Lakes. The relationship of temperature to gas-phase partial pressures was examined using the Clausius-Clapeyron equation, and environmental phase-transition energies were calculated for each of the pesticides. A first-order rate constant for the decline in gas-phase partial pressures was estimated from the regression, and corresponding regional atmospheric half-lives were determined. The atmospheric half-lives of the hexachlorocyclohexanes ranged from 2.2 yr for γ-HCH at Lake Michigan to 7.3 yr for γ-HCH at Lake Ontario. The half-life for hexachlorobenzene ranged from 3.3 yr at Lake Michigan to 12 yr at Lake Superior. The half-life for p,p′-DDT was less than 3 yr at Lakes Superior, Michigan, and Erie. A decreasing trend for chlordanes could only be discerned at Lakes Michigan, Erie, and Ontario, where halflives ranged from 3.2 yr for γ-chlordane at Lake Michigan and Lake Erie to 9.2 yr for trans-nonachlor at Lake Ontario. Using these half-lives and atmospheric concentrations, virtual elimination dates were estimated for the pesticides in the atmosphere. These virtual elimination dates ranged from about 2010 for p,p′-DDT to about 2060 for hexachlorobenzene. This study provides evidence that regulatory controls on pesticides have been effective in reducing the concentration of organochlorine pesticides in the environment.
Polychlorinated biphenyl (PCB) concentrations were measured in the atmosphere at six regionally representative sites near the five Great Lakes from 1990 to 2003 as part of the Integrated Atmospheric Deposition Network (IADN). Concentration data for several individual PCB congeners and for total PCBs were analyzed for temporal and spatial trends after correcting for the temperature dependency of the partial pressures. Atmospheric PCB concentrations are decreasing relatively slowly for tetra- and pentachlorinated congeners, an observation that is in agreement with primary emissions modeling. Relatively rapid decreases in PCB concentrations at the sites near Lakes Michigan and Ontario may reflect successful reduction efforts in Chicago and Toronto, respectively. Atmospheric PCB concentrations near Lakes Superior and Huron are now so low that the air and water concentrations may be close to equilibrium. Atmospheric PCB concentrations at sites near Lakes Michigan, Erie, and Ontario are relatively higher than those measured at sites near Lakes Superior and Huron. The highest PCB level was observed at the site near Lake Erie, most likely due to nearby urban activity. However, this relatively higher concentration is still 6-10 times lower than that previously reported at the Chicago site. A correlation between average gas-phase PCB concentration with local population indicates a strong urban source of PCBs. The temperature dependence of gas-phase PCB concentrations is similar at most sites except at Burnt Island on Lake Huron, where very low concentrations, approaching virtual elimination, prevent reliable temperature correlation calculations.
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