University of California, Los Angeles, Department of Atmospheric and Oceanic Sciences, Los Angeles, CA, USA; Pukyong National University, Department of Environmental Atmospheric Science, Busan, South Korea.
University of California, Los Angeles, Department of Atmospheric and Oceanic Sciences, Los Angeles, CA, USA.
Environ Pollut. 2018 Feb;233:235-245. doi: 10.1016/j.envpol.2017.10.055. Epub 2017 Nov 5.
Epidemiological studies have shown that exposure to traffic-related pollutants increases incidence of adverse health outcomes. Transit users in cities across the globe commonly spend 15-45 min or more waiting at transit stops each day, often at locations with high levels of pollution from traffic. Here, we investigate the characteristics of concentration profiles of ultrafine particles (UFP) with 5 m spatial resolution across intersections, to determine the best place to site transit stops to minimize exposures. Cross-intersection UFP profiles were derived from 1744 profiles covering 90 m before and after each intersection center with a mobile monitoring platform. Measurements were made at 10 signalized intersections located at six urban sites, each with a distinct built environment, during both mornings and afternoons. Measurements were made within 1.5 m of the sidewalk and approximately at breathing height (1.5 m above ground level) to approximate sidewalk exposures. UFP profiles were strongly influenced by high emissions from vehicle stops and accelerations, and peaked within 30 m of intersection centers; from there concentrations decreased sharply with distance. Peak concentrations averaged about 90% higher than the minima along the block. They were accompanied by more frequent and larger transient concentration spikes, increasing the chance of people near the intersection being exposed to both short-term extremely high concentration spikes and higher average concentrations. The decays are somewhat larger before the intersection than after the intersection, however as siting transit stops after intersections is preferred for smooth traffic flow, we focus on after the intersection. Simple time-duration exposure calculations combined with breathing rates suggest moving a bus stop from 20 to 40-50 m after the intersection can reduce transit-users' exposure levels to total UFP substantially, in proportion to the reciprocal of the magnitude of elevation at the intersection.
流行病学研究表明，接触与交通相关的污染物会增加不良健康结果的发生率。全球城市的交通使用者每天通常要在交通站等待 15-45 分钟或更长时间，而且通常是在交通污染水平高的地方。在这里，我们研究了具有 5m 空间分辨率的超细颗粒（UFP）浓度分布特征，以确定设置交通站的最佳位置，以最大限度地减少暴露。跨交叉口 UFP 分布是从 1744 个分布中得出的，这些分布涵盖了每个交叉口中心前后 90m 的范围，使用移动监测平台进行测量。在六个城市地点的 10 个信号交叉口进行了测量，每个地点的建筑环境都不同，分别在上午和下午进行了测量。测量在离人行道 1.5m 以内，大约在呼吸高度（离地面 1.5m）处进行，以近似人行道暴露。UFP 分布受车辆停止和加速时的高排放的强烈影响，在离交叉口中心 30m 以内达到峰值；从那里浓度随距离急剧下降。峰值浓度平均比街区内的最小值高出约 90%。它们伴随着更频繁和更大的瞬态浓度尖峰，增加了靠近交叉口的人暴露于短期极高浓度尖峰和更高平均浓度的机会。在交叉口之前的衰减比在交叉口之后的稍大，然而，由于为了顺畅的交通流而优先在交叉口之后设置交通站，因此我们重点关注交叉口之后的情况。简单的时间-持续时间暴露计算与呼吸率相结合表明，将公共汽车站从交叉口后 20 米移动到 40-50 米，可以大大降低公交使用者的总 UFP 暴露水平，与交叉口处的海拔高度的倒数成比例。
