Sensitivity of Source Apportionment of Urban Particulate Matter to Uncertainty in Motor Vehicle Emissions Profiles

Abstract

A sensitivity analysis was conducted to characterize sources of uncertainty in results of a molecular marker source apportionment model of ambient particulate matter using mobile source emissions profiles obtained as part of the Gasoline/Diesel PM Split Study. A chemical mass balance (CMB) model was used to determine source contributions to samples of fine particulate matter (PM2.5) collected over 3 weeks at two sites in the Los Angeles area in July 2001. The ambient samples were composited for organic compound analysis by the day of the week to investigate weekly trends in source contributions. The sensitivity analysis specifically examined the impact of the uncertainty in mobile source emissions profiles on the CMB model results. The key parameter impacting model sensitivity was the source profile for gasoline smoker vehicles. High-emitting gasoline smoker vehicles with visible plumes were seen to be a significant source of PM in the area, but use of different measured profiles for smoker vehicles in the model gave very different results for apportionment of gasoline, diesel, and smoker vehicle tailpipe emissions. In addition, the contributions of gasoline and diesel emissions to total ambient PM varied as a function of the site and the day of the week.

Source apportionment of elevated wintertime PAHs by compound-specific radiocarbon analysis

“…In fact, both indeno[cd]pyrene and benzo [ghi]perylene have been used in organic molecular marker-chemical mass balance models (MM-CMB) to apportion the contribution of gasolinepowered motor vehicle exhaust to atmospheric particulate organic carbon (Chow et al, 2007;Sheesley et al, 2007). Figure S1 (http://www.atmos-chem-phys.net/9/3347/ 2009/acp-9-3347-2009-supplement.pdf) illustrates that the PAH/OC ratio for benzo [ghi]perylene, in particular, is much higher for the two gasoline-powered motor vehicle exhaust average profiles (Lough et al, 2007;Rogge et al, 1993) in comparison to the same ratio for wood smoke emission profiles (Lee et al, 2005;Schauer et al, 2001;Fine et al, 2002Fine et al, , 2004 and reported diesel-powered motor vehicle exhaust (Rogge et al, 1993;Lough et al, 2007;Riddle et al, 2007). A further exploration of the apportionment of OC based on published PAH/OC ratios for motor vehicle exhaust is included in the Supplementary Material.…”

“…Specific PAHs may be more valuable as molecular markers than others in source apportionment models for OC when used in conjunction with more unique tracers such as hopanes and levoglucosan (Chow et al, 2007;Jaeckels et al, 2007;Lough and Schauer, 2007). However, more investigation into the sources of individual atmospheric PAHs is warranted to inform current source apportionment techniques.…”

Review of Recent Advances in Detection of Organic Markers in Fine Particulate Matter and Their Use for Source Apportionment

“…Uncertainties that are either too lenient or to stringent can have a significant effect on the PMF analysis outcome. [222][223][224] Finally, it should be pointed out that CMB and PMF analyses have been highlighted in this review because these are the two most commonly used source apportionment tools. However, they are certainly not the only tools and there will be a wide variety of uses of organic marker data in may applications in the future.…”

Insights into the Origin of Water Soluble Organic Carbon in Atmospheric Fine Particulate Matter

“…It should be noted that some uncertainty in the apportionment of OC to primary sources exists due to the sensitivity of CMB to the type and composition of source profiles used (Subramanian et al 2006;Lee and Russell 2007;Lough and Schauer 2007;Rutter et al 2008). Relevant to the work presented here, Sheesley et al (2007) demonstrated that although the apportionment of OC to biomass burning by CMB is sensitive to the choice of source profile (the reported standard deviation across 5 source profiles was a little greater than 30%), the uncertainty due to the choice of profile is similar to the underlying analytical uncertainty of the levoglucosan measurements, providing confidence in the apportionment of OC to biomass burning.…”