Kimbrough Sue, Hanley Tim, Hagler Gayle, Baldauf Richard, Snyder Michelle, Brantley Halley
Office of Research and Development, National Risk Management Research Laboratory, U.S. Environmental Protection Agency, 109 TW Alexander Dr., Research Triangle Park, NC, 27711, USA.
Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, 109 TW Alexander Dr., Research Triangle Park, NC, 27711, USA.
Air Qual Atmos Health. 2018;11(2). doi: 10.1007/s11869-017-0519-3.
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 32 and 60% higher than concentrations at 100 and 300 m from the roadway, respectively. Overall highest roadside (20-m site) BC concentrations were observed during the time period of 4 a.m.-8 a.m. under low-speed variable winds (3.02 μg/m) or downwind conditions (2.84 μg/m). The 20-m site BC concentrations under downwind conditions are 85% higher on weekday periods compared to weekends during the time period of 4 a.m.-8 a.m. Whereas total traffic volume was higher on weekdays versus weekends and differed by approximately 3% on weekdays versus weekends, similarly, the detected heavy-duty fraction was higher on weekdays versus weekends and 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 that 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 PM downwind concentration gradients indicates that the BC component contributes substantially to the PM increase in roadside environments. These results suggest that BC is an important indicator to assess the contribution of primary traffic emissions to near-road PM concentrations, providing opportunities to evaluate the feasibility and effectiveness of mitigation strategies.
主要公路附近空气污染水平升高是全球范围内持续受到公共卫生关注的话题。黑碳（BC）是柴油和汽油车辆排放的颗粒物（PM）的一个组成部分，通过基于过滤器的光吸收技术，在内华达州拉斯维加斯一条与主要公路垂直轨迹上的四个不同站点，连续测量了约16个月。在顺风条件下（西风），距离公路20米处的黑碳浓度分别比距离道路100米和300米处的浓度高32%和60%。总体而言，在凌晨4点至8点期间，在低速可变风（3.02μg/m）或顺风条件（2.84μg/m）下，观察到路边（20米处站点）黑碳浓度最高。在凌晨4点至8点期间，与周末相比，工作日顺风条件下20米处站点的黑碳浓度高出85%。尽管工作日的总交通量高于周末，且工作日与周末相差约3%，同样，检测到的重型车辆比例在工作日高于周末，且工作日与周末相差约21%。清晨时段风速较低，尽管一天中交通量最大的时候出现在晚些时候，但清晨时段的黑碳浓度仍较高。未观察到机场或附近干道的明显影响，当风向为东风时，300米处站点仍是四个站点网络中最低的。多元线性回归分析表明，重型交通量、轻型交通量、风速、工作日与周末、地表摩擦速度、环境温度以及背景黑碳浓度是路边黑碳浓度的重要预测因素。黑碳和细颗粒物顺风浓度梯度的比较表明，黑碳成分对路边环境中细颗粒物的增加有很大贡献。这些结果表明，黑碳是评估主要交通排放对近路细颗粒物浓度贡献的重要指标，为评估缓解策略的可行性和有效性提供了机会。
