National Dry Deposition Network: Second annual progress report (1988)

The National Dry Deposition Network is ultimately to provide long-term estimates of dry acidic deposition across the continental United States. Fifty sites operated during 1989, 41 in the east and 9 in the west. Weekly average atmospheric concentrations of sulfate, nitrate, ammonium, sulfur dioxide, and nitric acid were measured (using three stage filter packs) throughout the year, while sodium, potassium, calcium, and magnesium were measured from January through September. Results showed species-dependent variability in atmospheric concentrations from site to site, season to season, and day to night. In general SO{sub 4}{sup {minus}2}, NH{sub 4}{sup +}, SO{sub 2}, and HNO{sub 3} concentrations were much higher (factor 5-10) at eastern sites than at western. On the other hand, NO{sub 3}{sup {minus}}, Na{sup +}, K{sup +}, Ca{sup +}{sup 2}, and Mg{sup +}{sup 2} concentrations were frequently comparable at eastern and western sites. Average SO{sub 4}{sup {minus} 2}, NH{sub 4}{sup +}, and HNO{sub 3} concentrations were typically highest during summer and lowest during fall. In contrast, SO{sub 2} and NO{sub 3}{sup {minus}} were highest in winter and lowest in summer. Day/night variability was low for aerosols, but frequently pronounced for SO{sub 2} and HNO{sub 3}, especially during the summer and at sites surrounded bymore » complex terrain. Ozone data for 1988 and 1989 showed marked differences between years, with notably higher concentrations in 1988. Approximations of annual dry deposition rates for SO{sub 4}{sup {minus}2}, SO{sub 2}, NO{sub 3}{sup {minus}}, and HNO{sub 3} suggest that gaseous deposition greatly exceeds aerosol deposition and that dry fluxes are similar to wet deposition at numerous sites in the eastern U.S. Application of site-specific dry deposition models are needed to refine these estimates.« less