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 SO4(-2), NH4(+), SO2, and HNO3 concentrations were much higher (factor 5-10) at eastern sites than at western. On the other hand, NO3(-), Na(+), K(+), Ca(+2), and Mg(+2) concentrations were frequently comparable at eastern and western sites. Average SO4(-2), NH4(+), and HNO3 concentrations were typically highest during summer and lowest during fall. In contrast, SO2 and NO3(-) were highest in winter and lowest in summer. Day/night variability was low for aerosols, but frequently pronounced for SO2 and HNO3, especially during the summer and at sites surrounded by 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 SO4(-2), SO2, NO3(-), and HNO3 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.

"EPA/600/3-91/018." "Contract #68-02-4451." "March 1991." "Office of Research and Development, Atmospheric Research and Exposure Assessment Laboratory." "Environmental Science & Engineering, Inc." "Project Officer Ruldolph P. Boksleitner." Includes bibliographical references.