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PRECISION OF ATMOSPHERIC DRY DEPOSITION DATA FROM THE CLEAN AIR STATUS AND TRENDS NETWORK (CASTNET)
Citation:
Sickles II, J E. AND D. S. Shadwick. PRECISION OF ATMOSPHERIC DRY DEPOSITION DATA FROM THE CLEAN AIR STATUS AND TRENDS NETWORK (CASTNET). ATMOSPHERIC ENVIRONMENT 36(36-37):5671-5686, (2003).
Impact/Purpose:
Our main objective is to assess the exposure of selected ecosystems to specific atmospheric stressors. More precisely, we will analyze and interpret environmental quality (primarily atmospheric) data to document observable changes in environmental stressors that may be associated with legislatively-mandated emissions reductions.
Description:
A collocated, dry deposition sampling program was begun in January 1987 by the US Environmental Protection Agency to provide ongoing estimates of the overall precision of dry deposition and supporting data entering the Clean Air Status and Trends Network (CASTNet) archives Duplicate sets of dry deposition sampling instruments were installed adjacent to existing instruments and have been operated for various periods at I I collocated field sites. All sampling and operations were performed using standard CASTNet procedures. The current study documents the overall precision of CASTNet data based on collocated measurements made at paired sampling sites representative of sites across the network. These precision estimates include the variability for all operations from sampling to data storage in the archives Precision estimates are provided for hourly, instrumental ozone (0,) concentration and meteorological measurements, hourly model estimates of deposition Velocity (Vd) from collocated measurements of model inputs, hourly 0, deposition estimates, weekly filter pack determinations of selected atmospheric chemical species, and weekly estimates of Vi and deposition for each monitored filter pack species.
Conservative estimates of variability of weekly pollutant concentrations, expressed as coefficients of variation, depend on species: NO,- - 8. 1; HNO, - 6.4; SO, - 4.3; NH4' - 4. 1; SO,'- - 2.5; and 0, - 1. I %. Precision of estimates of weekly Vd from collocated measurements of model inputs also depends on the chemical species: HN03 - 6.3; aerosols - 5.2; SO, - 3.5; and 03 - 2. 1 %. Corresponding precision of weekly deposition estimates are: NO,- - 11.3; HN03- - 10-5; S04'- - 6.2; SO, and NH4' - 5.9; and 03 - 3.1%. Weekly precision of concentration, Vd estimates, and deposition estimates are comparable in magnitude and slightly smaller than the corresponding hourly values. Annual precision estimates, although uncertain due to their small sample size, are consistent, but slightly smaller than corresponding weekly values.