Using mass spectral source signatures to apportion exhaust particles from gasoline and diesel powered vehicles in a freeway study using UF-ATOFMS

Single particle mass spectrometry techniques such as aerosol time-of-flight mass spectrometry (ATOFMS) offer a unique approach for on-line source apportionment of ambient aerosols. Source signatures, or mass spectral “fingerprints”, have been obtained using ATOFMS from a variety of sources with an emphasis placed on distinguishing between emissions from different types of vehicles. In this study, the signatures from previous source tests of diesel powered heavy duty diesel vehicles (HDDV) and gasoline powered light duty vehicles (LDV) are matched to particle spectra acquired during a freeway-side study performed over a month in southern California to source apportion the particles. Using a relatively high ART-2a matching (vigilance) factor of 0.85, particle mass spectral signatures from the vehicle source studies matched 83% of the freshly emitted particles detected alongside the freeway. The particle contributions alongside the freeway in the ultrafine and accumulation size range (aerodynamic diameter=50–300 nm) were apportioned to 32% LDV, 51% HDDV, and 17% from other sources. This paper discusses the apportionment process used and the methods used for validation with peripheral instrumentation.