You are here:
“Transference Ratios” to Predict Total Oxidized Sulfur and Nitrogen Deposition – Part I, Monitoring Results
Citation:
Sickles, J. AND D. Shadwick. “Transference Ratios” to Predict Total Oxidized Sulfur and Nitrogen Deposition – Part I, Monitoring Results. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 77:1060-1069, (2013).
Impact/Purpose:
The US Environmental Protection Agency (EPA) is considering the use of “transference ratios” in the formulation of Secondary National Ambient Air Quality Standards (NAAQS) for oxides of nitrogen and oxides of sulfur as a means to estimate their total atmospheric deposition(US EPA, 2011). The concept of a “transference ratio,” introduced in US EPA (2011), was defined as the ratio of total (i.e., dry plus wet) deposition to the airborne concentration of the species of interest. This expresses the notion that the amount of an acidifying species deposited to the earth’s surface within a given area over a given period of time is proportional to the average airborne concentration of the acidifying species over the same area during the same time period, where the proportionality constant is called a transference ratio.
Description:
Use of model-predicted “transference ratios” is currently under consideration by the US EPA in the formulation of a Secondary National Ambient Air Quality Standard for oxidized nitrogen and oxidized sulfur. This term is an empirical parameter defined for oxidized sulfur (TS)as the ratio of the total oxidized sulfur deposition (from dry plus wet deposition) to the airborne concentration of oxidized sulfur. A 15-year record of weekly measured and data-derived quantities at 12 monitoring sites in the eastern US was examined to determine the variability of TS that might be expected from field measurements. Weekly TS displayed considerable variability that depended on site, season, and year, but according to ANOVA, most heavily on site and season. Using weekly data, the variability of deposition-related quantities and error propagation analysis of TS both suggest that variation in parameters related to wet deposition processes are generally more important than variation in parameters related to dry deposition processes in determining variation in TS. Correlations between airborne seasonal concentration of oxidized sulfur and the various components of seasonal deposition (i.e., dry, wet, and total) also underscore the strong influence that the variability in wet deposition processes can have on estimates of total deposition. Analysis of monitoring results suggests that 95% CI for TS using weekly results over several years for a specific site and season could be as large as ±235%, but only as large as ±33% using annual aggregates for a specific site. At the annual scale, a regression model of the form that incorporates a site-specific transference ratio, yielded estimates of total oxidized sulfur deposition to within ±25% of the monitored values ≥ 95% of the time. Since all of the major oxidized nitrogen species are not monitored regularly, a parallel analysis was limited to only the monitored oxidized nitrogen species. Nevertheless, fi