Fine Particle Episode Occurring in Montgomery County, TN, from September 5-15, 2005

摘要

The Tennessee Valley Authority (TVA) in cooperation with the state of Tennessee operated a continuous TEOM fine particle (PM_(2.5)) monitor in Montgomery County, TN which is approximately fifty miles north-northwest of Nashville, TN. This monitor recorded unusually elevated PM_(2.5) levels from September 5-15, 2005 compared to other monitors in and around the Tennessee Valley region. TVA and Tennessee Department of Environment & Conservation conducted a case study analysis of this episode considering the relationship between PM_(2.5) levels and various meteorological variables and potential local, regional and long range sources. Surface winds throughout the period were light and had a northerly component September 5-10, were variable September 11-12, and had a southerly component September 13-15, corresponding to a high pressure system slowly progressing from west to east throughout the period. Hourly dewpoint and relative humidity observations were relatively high (relative humidity generally above 90%) from 10pm-8am for each day, which corresponded well with several of the higher PM_(2.5) observations recorded in the pre-dawn hours. It is suspected that early morning inversions and stagnant conditions throughout the day associated with the high pressure system hindered the transport and dilution of PM_(2.5) levels caused by emissions from local sources such as agricultural burning, as well as long range transport of smoke from fires occurring in Idaho during the first half of the period. One concern of this episode is how unusually elevated PM_(2.5) levels occurring in a relatively short time period can influence the annual average for the site.