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Influential factors affecting black carbon trends at four sites of differing distance from a major highway in Las Vegas
Citation:
Kimbrough, Sue, T. Hanley, G. Hagler, R. Baldauf, M. Snyder, AND H. Brantley. Influential factors affecting black carbon trends at four sites of differing distance from a major highway in Las Vegas. Air Quality, Atmosphere & Health. Springer Netherlands, , Netherlands, 11(2):181-196, (2018).
Impact/Purpose:
Elevated air pollution levels adjacent to major highways are an ongoing topic of public health concern worldwide. Black carbon (BC), a component of particulate matter (PM) emitted by diesel and gasoline vehicles, was measured continuously via a filter-based light absorption technique over ~16 months at four different stations positioned on a perpendicular trajectory to a major highway in Las Vegas, NV. During downwind conditions (winds from the west), BC at 20 m from the highway was 38% and 92% higher than concentrations at 100 m and 300 m from the roadway, respectively. Overall highest roadside (20 m site) concentrations were observed during the time period of 4 AM – 8 AM under low speed variable winds (2.90 µg/m3) or downwind conditions (2.87 µg/m3), with downwind levels 66% higher on weekday periods compared to weekends. Whereas total traffic volume differed by approximately 3% on weekdays versus weekends, the detected heavy duty fraction differed by approximately 21% on weekdays versus weekend. Low wind speeds predominated during early morning hours, leading to higher BC concentrations during early morning hours despite the maximum traffic volume occurring later in the day. No noticeable impact from the airport or nearby arterial roadways was observed, with the 300 m site remaining the lowest of the four-site network when winds were from the east. Multivariate linear regression analysis revealed heavy duty traffic volume, light duty traffic volume, wind speed, weekday versus weekend, surface friction velocity, ambient temperature, and the background BC concentration were significant predictors of roadside BC concentrations. Comparison of BC and PM2.5 downwind concentration gradients indicates that the BC component contributes substantially to the PM2.5 increase in roadside environments. These results suggest that BC is an important indicator to assess the contribution of primary traffic emissions to near-road PM2.5 concentrations, providing opportunities to evaluate potential population exposure and the effectiveness of emissions reduction strategies.
Description:
Elevated air pollution levels adjacent to major highways are an ongoing topic of public health concern worldwide. Black carbon (BC), a component of particulate matter (PM) emitted by diesel and gasoline vehicles, was measured continuously via a filter-based light absorption technique over ~16 months at four different stations positioned on a perpendicular trajectory to a major highway in Las Vegas, NV. During downwind conditions (winds from the west), BC at 20 m from the highway was 38% and 92% higher than concentrations at 100 m and 300 m from the roadway, respectively. Overall highest roadside (20 m site) concentrations were observed during the time period of 4 AM – 8 AM under low speed variable winds (2.90 µg/m3) or downwind conditions (2.87 µg/m3), with downwind levels 66% higher on weekday periods compared to weekends. Whereas total traffic volume differed by approximately 3% on weekdays versus weekends, the detected heavy duty fraction differed by approximately 21% on weekdays versus weekend. Low wind speeds predominated during early morning hours, leading to higher BC concentrations during early morning hours despite the maximum traffic volume occurring later in the day. No noticeable impact from the airport or nearby arterial roadways was observed, with the 300 m site remaining the lowest of the four-site network when winds were from the east. Multivariate linear regression analysis revealed heavy duty traffic volume, light duty traffic volume, wind speed, weekday versus weekend, surface friction velocity, ambient temperature, and the background BC concentration were significant predictors of roadside BC concentrations. Comparison of BC and PM2.5 downwind concentration gradients indicates that the BC component contributes substantially to the PM2.5 increase in roadside environments. These results suggest that BC is an important indicator to assess the contribution of primary traffic emissions to near-road PM2.5 concentrations, providing opportunities to evaluate potential population exposure and the effectiveness of emissions reduction strategies.
URLs/Downloads:
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Influential factors affecting black carbon trends at four sites of differing distance from a major highway in Las Vegas