FINE, ULTRAFINE AND NANOPARTICLE TRACE ORGANIC COMPOSITIONS NEAR A MAJOR FREEWAY WITH A HIGH HEAVY DUTY DIESEL FRACTION 2007-24-0108

Individual organic compounds such as hopanes and steranes (originating in lube oil) and selected polycyclic aromatic compounds (PAHs) (generated via combustion) found in particulate emissions from vehicles have proven useful in source apportionment of ambient particulate matter. Currently, little ambient data exists for a majority of these species. Trace organic species in the size-segregated ultrafine (<0.18 µm) and accumulation (0.18-2.5 µm) particulate matter (PM) modes were measured during the winter season next to a busy Southern California freeway with significant (∼20%) diesel traffic. The ultrafine mode was further segregated into 4 size ranges (18-32 nm, 32-56 nm, 56-100 nm, and 100-180nm) with a NanoMOUDI low-pressure cascade impactor sampler. Both ambient and concentrated size-segregated impactor samples were taken in order to collect enough mass for chemical analysis. Accumulation and size segregated ultrafine mode particles were analyzed by various methods to investigate their chemical composition. Particle acidity and its relationship with size were also investigated by the ratio of measured and required ammonium for neutralization with nitrate and sulfate. All the measured organic species exhibited decreasing concentrations with size in the ultrafine mode. The most abundant PAHs in the ultrafine and accumulation modes were pyrene and benzo(ghi)perylene, whereas norhopane dominated the hopanes and steranes concentrations. This study is the first to present size-segregated organics species in the ultrafine range of PM in an ambient environment.