Impacts of the COVID-19 responses on traffic-related air pollution in a Northwestern US city

Abstract

This study evaluates the COVID-19 impacts on traffic-related air pollution, including ultrafine particles (UFPs), PM 2.5 , black carbon (BC), NO, NO 2 , NO x , 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 2.5 levels significantly decreased by 25% and 33%, relatively, while NO, NO 2 , NO x , 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 2.5 (−2% [95% CI: −1%, −3%]), NO, NO 2 , NO x (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 2.5 in the Seattle region, in contrast to the reverse trend from the direct empirical data comparison.

Changes in criteria air pollution levels in the US before, during, and after Covid-19 stay-at-home orders: Evidence from regulatory monitors

“…Our paper also adds to the existing literature exploring Covid-related impacts on air pollution and related activity levels ( Tobias et al, 2020 ; He et al, 2020 ; Venter et al, 2020 ; Kambalagere, 2020 ; Anjum, 2020 ; Mahato and Ghosh, 2020 ; Shrestha et al, 2020 ; Bauwens et al, 2020 ; Xu et al, 2020 ; Dutheil et al, 2020 ; Chauhan and Singh, 2020 ; Alfarra et al, 2020 ; Tanzer-Gruener et al, 2020 ; Berman and Ebisu, 2020 ; Goldberg et al, 2020 ; Xiang et al, 2020 ; Dantas et al, 2020 ; Bao and Zhang, 2020 ; Kerimray et al, 2020 ; Sharma et al, 2020 ; Chen et al, 2020 ; Li et al, 2020 ; Kugel and Feeser, 2020 ). Much of the news in the popular press regarding impacts of Covid on air pollution emphasizes that concentrations have improved during Covid ( CNN, 2020 ; Lewis, 2020 ; Hoeller, 2020 ; Freedman and Tierney, 2020 ; Monks, 2020 ; Mervosh et al, 2020 ); our investigation aims to test those claims using a national dataset of in-situ concentration measurements.…”

“…Analyses from individual locations, cities, or areas, can reveal different, potentially larger, impacts than the national-level trends are reported here. At a near-road monitoring station in Seattle, WA, concentrations of PM 2.5 , NO 2 and CO during Covid were 2–4% lower than pre-Covid concentrations ( Xiang et al, 2020 ). Data from a low-cost sensor network in Pittsburgh, PA, suggest that levels of PM 2.5 , NO 2 , and CO were 30–50% lower during than pre-Covid ( Dantas et al, 2020 ).…”

Regional Scale Impact of the COVID-19 Lockdown on Air Quality: Gaseous Pollutants in the Po Valley, Northern Italy

“…Recently, a number of papers have been published reporting the changes in concentration levels for certain pollutants in different areas worldwide, where light or heavy restrictive measures have been implemented [5]. Most of these works refer to China [6][7][8], Korea [9][10][11], India [12], Central [13,14], and South-East Asia [15], but also to Western European countries [16][17][18], Africa [19,20], and North and South America [21][22][23]. The few studies related waste treatment each accounted for 1% of the total annual emissions (about 185 Gg year -1 ).…”

Assessment of the COVID-19 Lockdown Effects on Spectral Aerosol Scattering and Absorption Properties in Athens, Greece

“…However, in areas significantly impacted by seasonal biomass burning or dust aerosols, AODs may remain unaffected or even increase during the lockdown period [36,37]. Beyond gaseous pollutants and AOD, there are some studies analyzing the changes in BC concentrations during the lockdown period [26,[38][39][40][41][42], which reported significant reductions (30-70%), but with large variability among regions. On the contrary, only a few works examined the changes in aerosol spectral absorption [43,44], while there is a lack of studies related to changes in spectral-scattering and single-scattering albedo (SSA).…”