Routine estimation and reporting of dry deposition for the U. S. A. Dry-Deposition Network

A National Dry Deposition Network (NDDN) was established in the United States during 1986 to document the magnitude, spatial variability, and trends in dry deposition of ozone and acidic particles and gases. Currently, the network consists of 50 stations: 41 in the eastern United States and 9 in the western United States. Dry deposition is not measured directly in the NDDN, but is estimated by an inferential approach, i.e., fluxes are calculated as the product of measured ambient concentration and modeled deposition velocity. The temporal resolution for the dry deposition calculations is weekly. Chemical species include ozone, sulfate, nitrate, ammonium, sulfur dioxide and nitric acid. Preliminary dry deposition calculations yielded the following observations: (1) calculated values of dry deposition for colocated sites are in good agreement suggesting good network precision, and (2) spatial patterns of SO2 and HNO3 dry deposition are consistent with emission patterns.