The Impact of Ambient Aerosols on Ozone as Measured by Ultraviolet Photometry

摘要

Despite intensive control efforts spanning three decades, ground level ozone continues to exceed the health-oriented National Ambient Air Quality Standard (NAAQS) in many parts of the United States. The U.S. EPA has identified both "reference" and "equivalent" measurement techniques in order to insure data uniformity on a National basis. This paper examines possible aerosol-induced bias in ambient ozone measurements made via ultraviolet photometry, an "equivalent" technique currently in use at almost all sites nationwide required by EPA to report ozone data. Although gas phase organics have demonstrable, positive effects on the UV method, little is known about the impact of fine aerosols (i.e., those in the 0.5 - 5.0 micron range) on the technique. Two photometric monitors were collocated in Madison, Connecticut at a site on Long Island Sound. Both monitors were configured and operated identically with the exception of the inlet line particle filters. One monitor was equipped with a fairly standard 5 micron Teflon~? filter while the other used a 0.45 micron Teflon membrane filter. Both monitors were operated throughout the summer of 2000. This paper examines the differences in ozone concentrations from the two monitors on a short-term (time of day) and long-term (weekly and monthly) basis. In addition to examining experimental results, this paper discusses implications of monitoring bias.