Potential effects of changes in precipitation and temperature on wet deposition in central Pennsylvania

Changes in regional climate can alter conditions that control the transport, chemical transformation, and eventual deposition of atmospheric pollutants. In Pennsylvania, climate change is projected to increase mean annual temperatures by 4°C and annual precipitation amounts by about 5% through 2100. The objective of this study was to determine how increases in temperature and precipitation would affect concentrations and wet deposition of SO 4 2−, NO 3 −, NH 4 +, and H + ions at a National Atmospheric Deposition Program site (NADP, PA15) in central Pennsylvania. Event-based wet deposition data were obtained from the Multi-State Atmospheric Power Production Pollution Study (MAP3S) monitoring program for the period 1976–1989. Forward stepwise regression was used to predict log-normal concentrations per event using mean temperature, precipitation, Julian Date, and interactions of temperature and precipitation with Julian Date as predictor variables. Julian Date was included to adjust for time trends in precipitation chemistry and climate data. Results were categorized by annual periods, growing season/dormant season, and synoptic climate types. Significant positive effects of temperature on concentration and deposition were found for SO 4 2−, NH 4 +, and H + but not for NO 3 −. Precipitation increases reduced the concentration of each ion due to dilution, but the lower concentration only minimally offset the increase in wet deposition due to the increased precipitation. The effects of climate change during the growing season (April–September) were projected to cause greater increases in the magnitude of SO 4 2−, NO 3 −, and H + concentrations and wet deposition than in the dormant season (October–March). Ammonium (NH 4 +) increases were greatest during the dormant season. Climate change effects on wet deposition were generally similar among synoptic climate types with the greatest effects occurring for cold fronts and warm fronts. The impacts of climate change for this central PA site could increase overall annual wet deposition of SO 4 2− by up to 29%, NO 3 − by up to 6%, NH 4 + by up to 23%, and H + by up to 17% through the year 2100, assuming that the statistical relationships hold true and that no changes in the emission of these ions occur.