Dry deposition inferential measurement techniques—II. Seasonal and annual deposition rates of sulfur and nitrate

Abstract

Abstract Since the autumn of 1984, a dry deposition research network has been operated to develop and refine methods to make defensible estimates of dry deposition rates of SO 2 , sulfate and nitrate (particulate and gaseous) on a routine basis. Ten of the sites are located in the eastern part of the U.S. while two are located in the western half. Annual dry deposition rates of sulfur (SO 2 +SO 4 2−2 ) are estimated to range from 2.5 kg ha −1 at Whiteface Mountain, NY to 14 kg ha −1 at Argonne, IL. The majority of deposited sulfur was delivered in the form of SO 2 . Deposition rates were highest during the summer season even though SO 2 concentrations peaked during the winter months because the estimated deposition velocities ( V d ) were much greater in the summer. Nearly all of the dry deposited nitrogen (HNO 3 +NO 3 − ) was in the form of HNO 3 . An annual cycle was not evident in the time series of nitrogen deposition rates. For both sulfur and nitrogen, dry deposition was estimated to provide between 30% and 50% of the total input from the atmosphere (wet+dry) for all sites in the eastern U.S.