Sources of ambient fine particulate matter at two community sites in Detroit, Michigan

Abstract

Detroit, Michigan is a non-attainment area of the annual PM 2.5 (particles ⩽2.5 μm in diameter) National Ambient Air Quality Standard (NAAQS), and contains a host of local pollution contributors including high diesel traffic from a nearby international border crossing. A source apportionment analysis was conducted using PM 2.5 data collected from 1999 to 2002 by the Community Action Against Asthma (CAAA) project in Detroit, Michigan. CAAA used a community-based participatory research approach to identify and address the environmental triggers for asthma among children residing in southwest and east Detroit. The data used for the study included 24-h measurements of PM 2.5 mass, elemental and organic carbon, and a suite of trace element species, along with hourly measurements of PM 2.5 mass and black carbon. Positive matrix factorization (PMF2) was used to quantitatively apportion the sources of ambient PM 2.5 at each of two Detroit community sites. Results showed that southwest Detroit PM 2.5 levels can be apportioned to seven source categories: secondary sulfate/coal combustion, gasoline vehicles, diesel vehicles, refinery/oil combustion, iron–steel manufacturing/waste incineration, automotive electroplating, and sewage sludge incineration that includes crustal material from runoff. The PMF2 model apportioned the east Detroit PM 2.5 data into five source categories: secondary sulfate/coal combustion, motor vehicles/combustion, refinery/oil combustion, iron–steel manufacturing/waste incineration, and automotive electroplating. For both locations, approximately over 60% of the PM 2.5 mass was attributed to secondary sulfate/coal combustion sources, approximately 30% to vehicular sources, and 1–5% to local industrial sources. The unexplained mass accounted for <2% of the measured PM 2.5 mass. This study illustrates that regional secondary sulfate/coal combustion and local motor vehicle emissions alone are enough for this mid-western US city to be in non-attainment for the annual PM 2.5 NAAQS.