PM2.5 Saturation Study in Northern Utah’s CacheValley

摘要

Logan (Cache County, Utah) is located in a broad valley, essentially bordered on all sidesby mountains rising up to elevations more than 1300 m above the valley floor. The PM2.5annual averages for 2001, 2002, and 2003 were 15.6 μg m-3, 14.7 μg m-3, and 8.4 μg m-3,respectively, for a 3-yr average of 12.9 μg m-3. The 98th percentile, 24-hr PM2.5concentrations for the same three years were 71.1 μg m-3 and 58.4 μg m-3, and 31.9 μg m-3, respectively, for a 3-yr average of 53.8 μg m-3. As such, the region seemed to be inonly slight danger of exceeding the PM2.5 U.S. National Ambient Air Quality Standards.However, January and February of 2004 saw 17 days with PM2.5 concentrations greaterthan the 24-hr standard (65 μg m-3), and nine days greater than 100 μg m-3. Finalregulatory data from 2004, shifted the 3-yr PM2.5 averages to 12.8 and 64.0 μg m-3,respectively. The high particulate concentrations, as measured at the single Logan citysampling site, as well as visual observations, suggested that the particulate pollution waslikely not an isolated problem centered around the sampling location, but more likelyhomogeneous throughout the valley. A small-scale PM10 homogeniety study during the2002/2003 suggested that the particulate was likely evenly spread throughout the valley.In order to further assess the homogeneity, fifteen portable PM2.5 samplers, along withtwo FRM samplers, were deployed during the winter of 2003/2004. Overall, althoughsome site-to-site variation seemed to occur, the entire valley was found to behomogeneous. On days when the PM2.5 was found to exceed the 24-hr NAAQS, onceagain the valley was found to be homogeneous (complete overlap within the total of the95% confidence interval error bars). However, on these days there was a more distinctpattern, with lower values tending to occur at the extreme north and south end of thevalley.