Ambient air monitoring of hazardous volatile organic compounds in Seattle, Washington neighborhoods trends and implications

Urban areas generally have higher levels of air pollutants than rural or remote areas. People living in these urban communities have higher risks of suffering from diseases linked to these air pollutants. In 2001, the United States Environmental Protection Agency conducted an Urban Air Toxics Pilot Study at various monitoring sites across the country. Seattle, the largest city in the state of Washington, was selected as one of four urban areas to participate in the study. The 2001 study established a network of monitoring sites that provided baseline concentrations of hazardous air pollutants including benzene, 1,3-butadiene, carbon tetrachloride, chloroform, perchloroethylene, trichloroethylene, formaldehyde, and acetaldehyde. The Washington State University Laboratory for Atmospheric Research, in cooperation with the Washington Department of Ecology, began measuring air toxics at Beacon Hill and Georgetown sites in Seattle in 2000 with collection of 24-hour integrated samples every sixth day through the EPA Pilot Study. The network was expanded to six sampling sites in 2001 with the same sampling frequency. Of the six sites, the Beacon Hill sampling station has a continuous record of hazardous VOC concentrations for the period 2000 to 2005. The first part of this research was aimed at characterizing the spatial and temporal trends in the ambient air concentrations of these hazardous air pollutants in Seattle, Washington. Statistical analysis showed that benzene, chloroform, perchloroethylene, trichloroethylene and acetaldehyde concentrations exhibited significant spatial variability while only temporal variability was observed for 1,3-butadiene and formaldehyde concentrations. A 67% reduction in ambient benzene levels observed in 2005 relative to the 2000 levels provided the motivation for further characterization of mobile source hazardous VOCs. The ambient levels of benzene, toluene, ethylbenzene and xylenes, which are primarily from mobile sources, were linked to various control programs implemented in Seattle. Elevated chloroform levels observed at sites close to water reservoirs prompted us to quantify the chloroform emissions from water reservoirs, which were found to be about 335 lb/yr. It is hoped that this study will provide baseline data and tools to evaluate the success or failure of current and future control programs in the Seattle area