Temporal trends and environmental influences on atmospheric pesticide and PAH concentrations measured near the Great Lakes

We investigate environmental influences on the atmospheric concentrations of pesticides and polycyclic aromatic hydrocarbons as measured by Integrated Atmospheric Deposition Network (IADN). We use multiple regression techniques to examine the temperature dependence and to elucidate temporal trends of atmospheric gas-phase partial pressures of these compounds. The temperature dependence is characterized using the Clausius-Clapeyron equation, and environmental phase-transition enthalpies are calculated. A first-order rate constant for a decline in gas-phase partial pressures is estimated from the regression, and corresponding regional atmospheric half-lives are determined. Using these estimated half-lives and atmospheric concentrations, virtual elimination dates are estimated for the pesticides in the atmosphere. In addition, the influence of local winds on gas-phase PAH concentrations is investigated and implications to atmospheric loadings are addressed.;The sampling and analytical requirements of observing statistically significant temporal trends in atmospheric pollutants are examined. Data precision and study duration are found to be the most important factors subject to experimental control. We define a detectable half-life as the longest half-life for which statistical significance can be observed for a given length of study. We then demonstrate how this can be calculated using data from IADN. We also show how to predict the length of study required to observe a statistically significant half-life.;We present evidence of recent agricultural pesticide use in atmospheric samples collected at Point Petre, Ontario. The evidence consists of a residual cycle of gamma-HCH concentrations that remains after correction for temperature effects. To characterize the residual cycle, we compare the fit of three periodic functions and include the function with the best fit in a model with temperature and time. The estimated parameters are used to identify agricultural use as the source of the residual cycle. We also examine the effect of agricultural use on the information typically extracted from Clausius-Clapeyron plots. The presence of an agricultural cycle maximizing near the temperature cycle results in an increased enthalpy of phase-transition, and the offset of the two cycles results in an increased apparent scatter in the data. Finally, the shape of the agricultural cycle imparts curvature to the normally linear relationship observed in Clausius-Clapeyron plots.