Evaluation of Weather Conditions for Methyl Bromide Ambient Air Monitoring in Monterey, Santa Cruz, and Kern Counties in Year 2000

摘要

Weather condition is one of the most important factors affecting spatial and temporal distributions of air pollutants, especially for short-term air dispersion. Abnormal weather conditions might lead to higher or lower ambient air concentrations than they would be under normal weather conditions. Therefore, test for normality of weather conditions during the air-monitoring period is an essential step for evaluating ambient air monitoring results. In this paper, a distance method was utilized to select a most representative weather station from available candidates. An array of meteorological elements were identified which affect air dispersion and transportation. A statistical method was employed to determine if the weather conditions during the air-monitoring period were significantly different from that of previous years. Using methyl bromide ambient air monitoring as a case study, this paper documents the methods, procedures, and results of weather analysis for Monterey, Santa Cruz and Kern Counties during ambient air monitoring periods for methyl bromide in year 2000. With a few exceptions, the meteorological elements and atmospheric stability factors such as wind speeds, wind directions and stability classes during the monitoring period were in the normal range. Although there were higher frequencies of stable atmospheric conditions in Monterey/ Santa Cruz Counties than in Kern County, weather conditions during the monitoring period were not significantly different from normal local weather conditions of previous years. Consequently, the subchronic air concentrations observed during the ambient air monitoring periods for methyl bromide in year 2000 was taken under typical weather conditions of those areas at that time of the year.