Comparison of four scanning mobility particle sizers at the Fresno Supersite

Size distributions of ambient aerosols at the Fresno Supersite were measured with four commercially available scanning mobility particle sizers (SMPS). TSI nano, TSI standard, Grimm, and MSP instruments were collocated at the Fresno Supersite and particle size distributions were measured continuously from August 18 through September 18, 2005. For particles with diameters between 10 and 200 nm, differences among hourly-average ambient particle concentrations ranged from 0% between the TSI nano and Grimm in the 30-50 nm size range to 39% between the Grimm and MSP in the 10-30 nm size range. MSP concentrations were 10-33% lower than those measured with the TSI standard for particles smaller than 200 nm. The TSI nano and TSI standard agreed to within 5% in their overlapping size range (10-84 nm). The TSI nano and Grimm agreed to within 40% for 5-10 nm particles.</p

Source apportionment of atmospheric particulate carbon in Las Vegas, Nevada, USA

A study was conducted to quantify wintertime contributions of source types to carbonaceous PM2.5 at four urban sites in the Las Vegas Valley, one of the most rapidly growing urban areas in the southwestern United States. Twenty-four hour average ambient samples were collected for mass, ions, elements, organic carbon (OC), elemental carbon (EC), and trace organic markers analysis. Additional measurements were made to determine diurnal patterns in light-absorbing black carbon (BC) as a marker for combustion sources. Carbonaceous PM sources of on-road gasoline vehicles, on-road diesel vehicles, and off-road diesel engines were characterized with their chemical profiles, as well as fuel-based emission factors, using an In-Plume Sampling System. The Effective Variance Chemical Mass Balance (EV-CMB) source apportionment model was applied to the ambient samples collected, using source profiles developed in this study as well as profiles from other relevant studies. Four main sources contributed to PM2.5 carbon within the Las Vegas Valley: (1) paved road dust, (2) on-road gasoline vehicles, (3) residential wood combustion, and (4) on-road diesel vehicles. CMB estimated that on-road mixed fleet gasoline vehicles are the largest source for OC and EC at all the sites. The contribution of paved road dust to both OC and EC was 5-10% at the four sites. On-road diesel vehicles contribute 22% of the OC and 34% of the EC at a site near the city center, which is located immediately downwind of a major freeway. Residential wood combustion is a more important source than on-road diesel vehicles for two residential neighborhood sites. These results are consistent with our conceptual model, and the research methodology may be applied to studying other urban areas.</p