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Analysis of Mobile Source Air Toxics (MSATS)–Near-Road VOC and CarbonylConcentrations
Citation:
Kimbrough, Sue, T. Palma, AND R. Baldauf. Analysis of Mobile Source Air Toxics (MSATS)–Near-Road VOC and CarbonylConcentrations. Presented at 2015 CRC Mobile Source Air Toxics (MSAT) Workshop, San Diego, CA, February 17 - 19, 2015.
Impact/Purpose:
This presentation examines data from a year-long study of measured near-road mobile source air toxic (MSAT) concentrations and compares these data with modeled 2005 National Air Toxic Assessment (NATA) results. Field study measurements were collected during a field campaign in Las Vegas, Nevada from mid-December, 2008 through mid-December, 2009. MSAT measurements included VOC (1,3-butadiene, benzene) and carbonyl (acrolein, acetaldehyde and formaldehyde) compounds. The data were compared with relevant census tract NATA estimates for 1,3-butadiene, benzene, acrolein, acetaldehyde and formaldehyde. NATA total ambient benzene concentrations were much higher relative to the measured benzene values, while NATA total acrolein values were much lower than measured acrolein values. NATA total acetaldehyde and formaldehyde concentrations for all wind conditions and downwind conditions were also much lower than measured acetaldehyde and formaldehyde concentrations. Plausible reasons for these differences include nearby sources influencing the measured values; meteorological influences may not be well captured by the NATA modeling regime; and atmospheric chemistry of measured compounds. Moreover, additional explanatory variables may be needed for certain urban areas in order to accurately disaggregate anthropogenic air toxics emissions (Kimbrough, et al., 2014). Predicted NATA acrolein values (total ambient) were a factor of 10 less than the measured values. Uncertainties in the sample collection and analysis of acrolein and uncertainties in existing emission inventories are the most probable explanations for these differences as well as secondary chemical reactions taking place (Kimbrough, et al., 2014).
Description:
This presentation examines data from a year-long study of measured near-road mobile source air toxic (MSAT) concentrations and compares these data with modeled 2005 National Air Toxic Assessment (NATA) results. Field study measurements were collected during a field campaign in Las Vegas, Nevada from mid-December, 2008 through mid-December, 2009. MSAT measurements included VOC (1,3-butadiene, benzene) and carbonyl (acrolein, acetaldehyde and formaldehyde) compounds. The data were compared with relevant census tract NATA estimates for 1,3-butadiene, benzene, acrolein, acetaldehyde and formaldehyde. NATA total ambient benzene concentrations were much higher relative to the measured benzene values, while NATA total acrolein values were much lower than measured acrolein values. NATA total acetaldehyde and formaldehyde concentrations for all wind conditions and downwind conditions were also much lower than measured acetaldehyde and formaldehyde concentrations. Plausible reasons for these differences include nearby sources influencing the measured values; meteorological influences may not be well captured by the NATA modeling regime; and atmospheric chemistry of measured compounds. Moreover, additional explanatory variables may be needed for certain urban areas in order to accurately disaggregate anthropogenic air toxics emissions (Kimbrough, et al., 2014). Predicted NATA acrolein values (total ambient) were a factor of 10 less than the measured values. Uncertainties in the sample collection and analysis of acrolein and uncertainties in existing emission inventories are the most probable explanations for these differences as well as secondary chemical reactions taking place (Kimbrough, et al., 2014).