Characterization of particulate matter emissions from on-road gasoline and diesel vehicles using a soot particle aerosol mass spectrometer

摘要

Particulate matter (PM) emissions were measured in July 2010 from on-roadmotor vehicles driving through a highway tunnel in the San Francisco Bayarea. A soot particle aerosol mass spectrometer (SP-AMS) was used to measurethe chemical composition of PM emitted by gasoline and diesel vehicles athigh time resolution. Organic aerosol (OA) and black carbon (BC)concentrations were measured during various time periods that had differentlevels of diesel influence, as well as directly in the exhaust plumes ofindividual heavy-duty (HD) diesel trucks. BC emission factor distributionsfor HD trucks were more skewed than OA distributions ( = 293), with thehighest 10% of trucks accounting for 56 and 42% of total measured BCand OA emissions, respectively. OA mass spectra measured for HD truckexhaust plumes show cycloalkanes are predominate in exhaust OA emissionsrelative to saturated alkanes (i.e., normal and iso-paraffins), suggestingthat lubricating oil rather than fuel is the dominant source of primaryorganic aerosol (POA) emissions in diesel vehicle exhaust. This finding issupported by the detection of trace elements such as zinc and phosphorus inthe exhaust plumes of individual trucks. Trace elements were emittedrelative to total OA at levels that are consistent with typical weightfractions of commonly used additives present in lubricating oil. Acomparison of measured OA and BC mass spectra across various samplingperiods revealed a high degree of similarity in OA and BC emitted bygasoline and diesel engines. This finding indicates a large fraction of OAin gasoline exhaust is lubricant-derived as well. The similarity in OA andBC mass spectra for gasoline and diesel engine exhaust is likely to confoundambient source apportionment efforts to determine contributions to airpollution from these two important sources.