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Diesel and gasoline powered motor vehicle emissions were quantified through both ambient measurements and source-based emissions measurements. Ambient ultrafine particulate matter was measured and chemically speciated for a source apportionment analysis to identify the vehicular contributions at an urban city in California. The efforts of the Emissions Reduction Plan for Ports and Goods Movement in California have been realized through the comparison of ultrafine particulate matter contributions from old-technology diesel engines during different phases of the regulation implementation between years 2009 and 2010. Volatility of primary organic aerosols from gasoline powered motor vehicles was investigated using a series of thermodenuder experiments and particle evaporation modeling. The behaviors and the compositions of gas- and particle-phase motor vehicle emissions under atmospherically relevant conditions were also examined. These analyses will aid scientists and regulators in properly assessing the current state of vehicular emissions regulations, aid in particulate matter exposure studies, improve the understanding of the characteristics of vehicular emissions, and determine the effects of atmospheric parameters on the production and the partitioning of organic pollutants.
Final report for California Air Resources contracts 04-347 and 05-346. For abstract and link to full text, please visit: http://www.arb.ca.gov/research/single-project.php?row_id=64430
Emission factors for black carbon (BC) and particle number (PN) were measured from 226 individual heavy-duty (HD) diesel-fueled trucks driving through a 1 km-long California highway tunnel in August 2006. Emission factors were based on concurrent increases in BC, PN, and CO2B concentrations (measured at 1 Hz) that corresponded to the passage of individual HD trucks. The distributions of BC and PN emission factors from individual HD trucks are skewed, meaning that a large fraction of pollution comes from a small fraction of the in-use vehicle fleet. The highest-emitting 10% of trucks were responsible for ≈ 40% of total BC and PN emissions from all HD trucks. BC emissions were log-normally distributed with a mean emission factor of 1.7 g kg −1 and maximum values of ≈ 10 g kg−1. Corresponding values for PN emission factors were 4.7 x 1015 and 4 x 1016 kg−1. There was minimal overlap among high-emitters of these two pollutants: only 1 of the 226 HD trucks measured was found to be among the highest 10% for both BC and PN. Monte Carlo resampling of the distribution of BC emission factors observed in this study revealed that uncertainties (1[sigma]) in extrapolating from a random sample of n HD trucks to a population mean emission factor ranged from ± 43% for n = 10 to ± 8% for n = 300, illustrating the importance of sufficiently large vehicle sample sizes in emissions studies. Studies with low sample sizes are also more easily biased due to misrepresentation of high-emitters. As vehicles become cleaner on average in future years, skewness of the emissions distributions will increase, and thus sample sizes needed to extrapolate reliably from a subset of vehicles to the entire in-use vehicle fleet are expected to become more of a challenge.