Air pollution in urban locations incorporates many components that originate from a wide range of industrial, motor vehicle, and natural emissions sources. Because some of these components include toxic compounds known or suspected to be carcinogenic, the U.S. Environmental Protection Agency (EPA) continues to encourage state and local agencies to understand and appreciate the nature and extent of potentially toxic air pollution in urban locations. To achieve this goal, EPA sponsors the Urban Air Toxics Monitoring Program (UATMP) to characterize the composition and magnitude of urban air pollution through extensive ambient air monitoring. Since the inception of UATMP in 1987, many environmental and health agencies have participated in the UATMP to assess the causes and effects of air pollution within their jurisdictions. This report summarizes and interprets the 2004 UATMP monitoring effort, which included 12 months of 6- and 12-day measurements of ambient air quality at 44 monitoring sites in or near 29 urban/rural locations including 21 metropolitan statistical areas (MSAs). Much of the analysis and data interpretation in this report focuses on compound-specific data trends. Since 1987, the UATMP annual sampling cycle typically began in September and ended in August of the following calendar year. However, for the 2001 program year, ERG began sampling in January 2001 and ended all sampling at the end of December 2001. The 2002-2004 program years follow the same convention as 2001. The contents of this report provide both a qualitative overview of air pollution at selected urban locations and a quantitative analysis of the factors that appear to affect urban air quality most significantly. This report also focuses on data trends at each of the 44 different air sampling locations, a site-specific approach that allows for much more detailed analyses of the factors (e.g., motor vehicle emission sources, industrial sources, natural sources) that affect air quality differently from one urban center to the next.

Project officer: Margaret Dougherty. "December 2005." "Prepared for Margaret Dougherty and Mike Jones, Office of Air Quality Planning and Standards, Research Triangle Park, NC 27711." "EPA-454/R-06-001." PB2006-109712 Includes bibliographical references (p. 23-1-23-3) Final report. "Through its Office of Air Quality Planning and Standards, the U.S. Environmental Protection Agency funded and managed the research described in this report under EPA Contract No. 68-D-03-049 to Eastern Research Group"--p.ii