LOCAL BACKGROUND LEVELS OF CARBON-MONOXIDE IN AN URBAN AREA

The objective of this study was to obtain a better understanding of ca rbon monoxide (CO) concentrations immediately upwind of urban roadways , the ''local background'' values, and how these concentrations depend upon the surrounding traffic and the general meteorology. Measurement s were made at seven sites in Seattle, WA during the winter of 1993. L ocal background CO concentrations were characterized by an absence of short term fluctuations, a steady buildup during the 3 p.m. to 11 p.m. period, and a lack of spatial gradients in the 8-h average values. Di stinctly different log-normal distributions of the 8-h averages were o bserved for ''trafficked'' sites versus ''urban park'' sites, with mea n values of 1.6 and 1.0 ppm respectively. A simple regression model wa s developed to predict the local background CO that includes distance from roadway, average daily traffic of nearby roadways, and the freque ncy of occurrence of low windspeeds (R(2) = 0.74; F = 170). Copyright (C) 1996 Elsevier Science Ltd