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CASTNET NATIONAL DRY DEPOSITION NETWORK - 1990-1992 STATUS REPORT
Citation:
Baumgardner, R. CASTNET NATIONAL DRY DEPOSITION NETWORK - 1990-1992 STATUS REPORT. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-95/086.
Description:
The National Dry Deposition Network (NDDN) was established to provide long-term estimates of dry acidic deposition across the continental United States. ifty routine sites were operational from 1990 to 1992, including 41 sites in the eastern United States and 9 sites in the western United States. ach site was equipped with sensors for continuous measurements of ozone (O3) and meteorological variables required for estimation of dry deposition rates. eekly average atmospheric concentrations of particulate sulfate (SO2-4), particulate nitrate (NO-3), particulate ammonium (NH+4), sulfur dioxide (SO2), and nitric acid (HNO3) were measured at all sites and wet deposition of acidity and related species were measured at selected sites. wo methods development sites were installed during 1991 to evaluate: 1) comparability of United States and Canadian air quality measurements, and 2) effects of terrain on pollutant concentration and deposition. outine application of an inferential model for calculation of deposition velocities and dry deposition fluxes was also begun. tmospheric concentration data show species-dependent variability in space and time. n general, the highest concentrations are observed in the northeast and midwest, and these are a factor of 5 to 10 times higher than those observed in the west. ignificant concentration gradients are also observed from the northeast through upper northeast and midwest through upper midwest. nnual average concentrations of most species decreased from 1989 to 1992 in all subregions of the network.