Comparison of precipitation chemistry in the Central Rocky Mountains, Colorado, USA

Volume-weighted mean concentrations of nitrate (NO3-), ammonium (NH4+), and sulfate (SO42-) in precipitation were compared at high-elevation sites in Colorado from 1992 to 1997 to evaluate emission source areas to the east an d west of the Rocky Mountains. Precipitation chemistry was measured by two sampling methods, the National Atmospheric Deposition Program/National Tren ds Network (NADP/NTN) and snowpack surveys at maximum accumulation. Concent rations of NO3- and SO42- in winter precipitation were greater on the weste rn slope of the Rockies, and concentrations of NO3- and NH4+ in summer prec ipitation were greater on the eastern slope. Summer concentrations in gener al were almost twice as high as winter concentrations. Seasonal weather pat terns in combination with emission source areas help to explain these diffe rences. This comparison shows that high-elevation ecosystems in Colorado ar e influenced by air pollution emission sources located on both sides of the Continental Divide. It also suggests that sources of nitrogen and sulfur l ocated east of the Divide have a greater influence on precipitation chemist ry in the Colorado Rockies. Published by Elsevier Science Ltd.