Source areas for chemical components in Minnesota rain

Air parcel back trajectories were used to quantify the contributions of major source areas to the chemical composition of rainwater in an area of central Minnesota. Air masses arriving from the SW contributed the majority of the rain, and the rain contained the highest concentrations of the chemical components. However, rain from the SW quadrant was less acidic than rain arriving from other quadrants because it contained a disproportionate amount of alkaline cations. It was inferred from meteorological evidence that components in rain arriving at the study site from the SW quadrant may have come from eastern and southern U.S.A. sources and been transported around a high pressure system to Minnesota. Rain from the SE quadrant was the most acidic. Concentrations of substances in rain arriving from the NW were higher than expected, consistent with a possible impact from western coal development.