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Analysis of mobile source air toxics (MSATs)–Near-Road VOC and carbonyl concentrations
Citation:
Kimbrough, Sue, T. Palma, AND R. Baldauf. Analysis of mobile source air toxics (MSATs)–Near-Road VOC and carbonyl concentrations. JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION. Air & Waste Management Association, Pittsburgh, PA, 64(3):349-359, (2014).
Impact/Purpose:
This paper examines long-term trends of measured near-road MSAT concentrations with modeled 2005 NATA results. These VOC (1,3-butadiene, benzene) and carbonyl (acrolein, acetaldehyde and formaldehyde) measurements were collected during a field study in Las Vegas, Nevada from mid-December, 2008 through mid-December, 2009. The most pronounced spatial gradient occurred for formaldehyde under all wind conditions and for only downwind conditions. When pollutant concentrations were normalized to the relevant 20 m site value, 1,3-butadiene and benzene had the most pronounced spatial gradients. However, median concentrations were often higher at the site furthest from the roadway suggesting that other sources, particularly the adjacent parking lot, contributed to emissions of these pollutants. As a consequence, the typical spatial gradient change of concentrations was not well defined.
Description:
Exposures to mobile source air toxics (MSATs) have been associated with numerous adverse health effects. While thousands of air toxic compounds are emitted from mobile sources, a subset of compounds are considered high priority due to their significant contribution to cancer and non-cancer health risks and the contribution of mobile sources to total exposure as evaluated by EPA's National Air Toxics Assessments (NATA). These pollutants include benzene, 1,3-butadiene, ethylbenzene, acrolein, acetaldehyde, formaldehyde, naphthalene, polycyclic organic matter and diesel particulate matter/organic gases. This study provided year-long trends of benzene, 1,3-butadiene, acrolein, acetaldehyde, and formaldehyde in Las Vegas, Nevada, USA. Results indicated that MSAT concentrations often did not exhibit typical trends of other primary emitted pollutants in this study. Instead, other mobile sources beyond the highway of interest contributed to the measured values, including a major arterial road, large commercial airport, and a nearby parking lot. The data were compared with relevant census tract National Air Toxics Assessment (NATA) estimates, with estimated ambient 1,3-butadiene concentrations similar to the measured values. Measured benzene values were much lower relative to the NATA total ambient benzene concentrations. Measured acrolein values were much higher relative to the NATA total acrolein concentrations. Measured acetaldehyde and formaldehyde values were also higher relative to the NATA total acetaldehyde and formaldehyde concentrations for all wind conditions and downwind conditions. Some possible explanations for these differences include nearby sources influencing the measured values; meteorological influences may not be well captured by the NATA modeling regime; and additional explanatory variables may be needed for certain urban areas in order to accurately disaggregate anthropogenic air toxics emissions.
