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CORRECTION FACTORS FOR COVARIANCE BETWEEN CONCENTRATION AND DEPOSITION VELOCITY ON CASTNET HNO3 DEPOSITION ESTIMATES
Citation:
Sickles II, J E. AND D. S. Shadwick. CORRECTION FACTORS FOR COVARIANCE BETWEEN CONCENTRATION AND DEPOSITION VELOCITY ON CASTNET HNO3 DEPOSITION ESTIMATES. WATER, AIR, & SOIL POLLUTION, AN INTERNATIONAL JOURNAL OF ENVIRONMENTAL POLLUTION 1(3):29-38, (2002).
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:
The covariance between hourly concentration (C) and deposition velocity (V) for various atmospheric; species may act to bias the, deposition (D) computed from the product of the weekly average C and 'V. This is a potential problem for the CASTNet filter pack (FP) species, nitric acid (H.NO3'. Using ozone (03) behavior as a surrogate for the FP species, correction factors (CF) are developed to estimate this bias. Weekly CF for 03 depend on both site and season, and seasonal average weekly, C.F for 03 at a given site may be as high as 1.25. The seasonal magnitude of these CF is generally largest in summer and is ordered> summer > fall > spring > winter. The CF is driven to a large extent by the diurnal correlation between C and V (i.e., both are generally higher during the day and lower at night). However, since the diurnal C profile at elevated sites is relatively constant, the resulting correlation between C and V is small, and the CF at montane sites is generally negligible. The sampling protocol using daytime integrated sampling for a week and nighttime integrated sampling for a week captures the diurnal correlation between C and V adequately may be used to aggregate relatively unbiased weekly D estimates. Day-night CF for 03 are close to unity, and limited results suggest similar behavior for HN03. Using these limited FP results, the site- and seasonally-.specific weekly CF for 03 are refined to estimate the corresponding CF for HN03. Worst-case adjustments for IIN03 as high as 30% are indicated for summer periods at a given site.