A Method of Developing Background Concentrations from Ambient Monitors with Significant Source Impacts

摘要

American Electric Power Service Corporation (AEPSC) requested the assistance of TRC Environmental Corp. (TRC) to assist in refining a methodology to estimate background SO_2 values for air quality modeling purposes. It was believed that this methodology was potentially more robust than the directional analysis method described in 40 CFR 51 Appendix W. This work used hourly monitored concentrations of SO_2 from three years along with concurrent one hour and one minute meteorologic data collected within 1 km of the monitor site. For this analysis, concentrations were excluded from the "background" sample if any of eight known sources of SO_2 were determined to be upwind of the monitor. As an additional means of reducing the number of hours that would need to be screened, a cutoff value of 10 ppb was selected as a minimum value for those hours that would be examined. This method has proven highly successful at the initial site. It has also been used in a reduced form in two other cases, even where concurrent one minute meteorologic data was not present.