Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, WA 98195, United States.
Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, WA 98195, United States.
Sci Total Environ. 2020 Dec 10;747:141325. doi: 10.1016/j.scitotenv.2020.141325. Epub 2020 Jul 28.
This study evaluates the COVID-19 impacts on traffic-related air pollution, including ultrafine particles (UFPs), PM, black carbon (BC), NO, NO, NO, and CO in a Northwestern US city. Hourly traffic, air pollutants, and meteorological data on/near a major freeway in the downtown of Seattle, Washington, were collected for five weeks before and ten weeks after the Washington Stay Home Order (SHO) was enacted, respectively (February 17-May 31, 2020). The pollutants between pre- and post-SHO periods were compared, and their differences were statistically tested. Besides, first-order multivariate autoregressive (MAR(1)) models were developed to reveal the impacts specific to the change of traffic due to the COVID-19 responses while controlling for meteorological conditions. Results indicate that compared with those in the post-SHO period, the median traffic volume and road occupancy decreased by 37% and 52%, respectively. As for pollutants, the median BC and PM levels significantly decreased by 25% and 33%, relatively, while NO, NO, NO, and CO decreased by 33%, 29%, 30%, and 17%, respectively. In contrast, neither size-resolved UFPs nor total UFPs showed significant changes between the two periods, although larger particles (≥115.5 nm) decreased by 4-29%. Additionally, significant differences were found in meteorological conditions between the two periods. Based on the MAR(1) models, controlling for meteorological conditions, the COVID-19 responses were associated with significant decreases in median levels of traffic-related pollutants including 11.5-154.0 nm particles (ranging from -3% [95% confidence interval (CI): -1%, -4%] to -12% [95% CI: -10%, -14%]), total UFPs (-7% [95% CI: -5%, -8%]), BC (-6% [95% CI: -5%, -7%]), PM (-2% [95% CI: -1%, -3%]), NO, NO, NO (ranging from -3% [95% CI: -2%, -4%] to -10% [95% CI: -18%, -12%]), and CO (-4% [95% CI, -3%, -5%]). These findings illustrate that the conclusion of the COVID-19 impacts on urban traffic-related air pollutant levels could be completely different in scenarios whether meteorology was adjusted for or not. Fully adjusting for meteorology, this study shows that the COVID-19 responses were associated with much more reductions in traffic-related UFPs than PM in the Seattle region, in contrast to the reverse trend from the direct empirical data comparison.
本研究评估了 COVID-19 对美国西北部一个城市交通相关空气污染的影响，包括超细颗粒 (UFPs)、PM、黑碳 (BC)、NO、NO、NO 和 CO。在华盛顿州西雅图市中心的一条主要高速公路上，分别收集了 COVID-19 限制措施（华盛顿州居家令）实施前五周和实施后十周的每小时交通量、空气污染物和气象数据（2020 年 2 月 17 日至 5 月 31 日）。比较了限制措施前后两个时期的污染物，并对其差异进行了统计检验。此外，还开发了一阶多元自回归（MAR(1)）模型，以揭示 COVID-19 应对措施对交通变化的影响，同时控制气象条件。结果表明，与限制措施实施后相比，交通量中位数和道路占有率分别下降了 37%和 52%。至于污染物，BC 和 PM 水平的中位数分别显著下降了 25%和 33%，而 NO、NO、NO 和 CO 分别下降了 33%、29%、30%和 17%。相比之下，两个时期之间的大小分辨 UFPs 或总 UFPs 均无显著变化，尽管较大颗粒（≥115.5nm）减少了 4-29%。此外，两个时期的气象条件也存在显著差异。基于 MAR(1)模型，在控制气象条件的情况下，COVID-19 应对措施与交通相关污染物水平的显著下降有关，包括 11.5-154.0nm 颗粒（范围为-3%[95%置信区间（CI）：-1%，-4%]至-12%[95% CI：-10%，-14%]）、总 UFPs（-7%[95% CI：-5%，-8%]）、BC（-6%[95% CI：-5%，-7%]）、PM（-2%[95% CI：-1%，-3%]）、NO、NO、NO（范围为-3%[95% CI：-2%，-4%]至-10%[95% CI：-18%，-12%]）和 CO（-4%[95% CI，-3%，-5%]）。这些发现表明，在是否调整气象条件的情况下，对 COVID-19 对城市交通相关空气污染物水平影响的结论可能完全不同。充分考虑气象因素后，本研究表明，与西雅图地区直接经验数据比较所显示的相反趋势相比，COVID-19 应对措施与交通相关 UFPs 而非 PM 的减少量更为相关。
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