DRY DEPOSITION INFERENTIAL MEASUREMENT TECHNIQUES .2. SEASONAL AND ANNUAL DEPOSITION RATES OF SULFUR AND NITRATE

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 SO2, 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 (SO2 + SO4(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 SO2. Deposition rates were highest during the summer season even though SO2 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 (HNO3 + NO3-) was in the form of HNO3. 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.