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Co-occurrence of Sulfur Dioxide with Nitrogen Dioxide

Because elevated SO2 concentrations are mostly associated with industrial activities (U.S. Environmental Protection Agency, 1992), co-occurrence observations are usually associated with monitors located near these types of sources. Lefohn and Tingey (1984) reported that, for the rural and nonrural monitoring sites investigated, most of the sites analyzed experienced fewer than 10 co-occurrences (when both pollutants were present at an hourly average concentration greater than or equal to 0.05 ppm) for SO2 and NO2. Figure 1 illustrates the simultaneous co-occurrence results reported by Lefohn and Tingey (1984).

Using 2001 data from the EPA AQS database, patterns that showed air pollutant pairs of SO2/NO2 appearing at the same hour of the day at concentrations equal to or greater 0.05 ppm were characterized. The data were not segregated by location settings categories (i.e., rural, suburban, and urban and center city) or land use types (i.e., agricultural, commercial, desert, forest, industrial, mobile, or residential). Data capture was not a consideration in the analysis. In 2001, there were 188 monitoring sites that co-monitored SO2 and NO2. Because of possible missing hourly average concentration data during periods when co-monitoring may have occurred, no attempt was made to characterize the number of co-occurrences in the 0 category. Thus, co-occurrence patterns were identified for those monitoring sites that experienced one or more co-occurrences.

Figure 1. The co-occurrence pattern for sulfur dioxide and nitrogen dioxide (Source: Lefohn and Tingey, 1984).

Figure 2 illustrates the results of the analysis. Similar to the results reported by Lefohn and Tingey (1984), most of the co-located monitoring sites analyzed, using the 2001 data, experienced fewer than 10 co-occurrences (when both pollutants were present at an hourly average concentration greater than or equal to 0.05 ppm).

Figure 2. The co-occurrence pattern for sulfur dioxide and nitrogen dioxide using 2001 data from AQS.

The information on this web page can be referenced as Lefohn, A.S. (2006). Co-occurrence of Sulfur Dioxide with Nitrogen Dioxide. http://www.asl-associates.com/co_occurrence_SO2_NO2.htm.

References

Lefohn, A. S.; Tingey, D. T. (1984) The co-occurrence of potentially phytotoxic concentrations of various gaseous air pollutants. Atmos. Environ. 18: 2521-2526.

Lefohn, A. S.; Davis, C. E.; Jones, C. K.; Tingey, D. T.; Hogsett, W. E. (1987) Co-occurrence patterns of gaseous air pollutant pairs at different minimum concentrations in the United States. Atmos. Environ. 21: 2435-2444.

U.S. Environmental Protection Agency. (1992) National Air Quality and Emissions Trends Report, 1991. Research Triangle Park, NC: U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards; report no. EPA/450-R-92-001. Available from: NTIS, Springfield, VA; PB93-143998.

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