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Title: How transportation restriction shapes the relationship between ambient nitrogen dioxide and covid-19 transmissibility : an exploratory analysis
Authors: Han, L
Zhao, S
Cao, P
Chong, MKC
Wang, J
He, D 
Deng, X
Ran, J
Issue Date: Jul-2021
Source: Frontiers in public health, July 2021, v. 9, 697491
Abstract: Background: Several recent studies reported a positive (statistical) association between ambient nitrogen dioxide (NO2) and COVID-19 transmissibility. However, considering the intensive transportation restriction due to lockdown measures that would lead to declines in both ambient NO2 concentration and COVID-19 spread, the crude or insufficiently adjusted associations between NO2 and COVID-19 transmissibility might be confounded. This study aimed to investigate whether transportation restriction confounded, mediated, or modified the association between ambient NO2 and COVID-19 transmissibility.
Methods: The time-varying reproduction number (Rt) was calculated to quantify the instantaneous COVID-19 transmissibility in 31 Chinese cities from January 1, 2020, to February 29, 2020. For each city, we evaluated the relationships between ambient NO2, transportation restriction, and COVID-19 transmission under three scenarios, including simple linear regression, mediation analysis, and adjusting transportation restriction as a confounder. The statistical significance (p-value < 0.05) of the three scenarios in 31 cities was summarized.
Results: We repeated the crude correlational analysis, and also found the significantly positive association between NO2 and COVID-19 transmissibility. We found that little evidence supported NO2 as a mediator between transportation restriction and COVID-19 transmissibility. The association between NO2 and COVID-19 transmissibility appears less likely after adjusting the effects of transportation restriction.
Conclusions: Our findings suggest that the crude association between NO2 and COVID-19 transmissibility is likely confounded by the transportation restriction in the early COVID-19 outbreak. After adjusting the confounders, the association between NO2 and COVID-19 transmissibility appears unlikely. Further studies are warranted to validate the findings in other regions.
Keywords: China
Nitrogen dioxide
Reproduction number
Publisher: Frontiers Research Foundation
Journal: Frontiers in public health 
ISSN: 2296-2565
DOI: 10.3389/fpubh.2021.697491
Rights: © 2021 Han, Zhao, Cao, Chong, Wang, He, Deng and Ran. This is anopen-access article distributed under the terms of the Creative Commons AttributionLicense (CC BY) ( The use, distribution or reproduction in other forums is permitted,provided the original author(s) and the copyright owner(s) are credited and that theoriginal publication in this journal is cited, in accordance with accepted academicpractice. No use, distribution or reproduction is permitted which does not complywith these terms.
The following publication Han L, Zhao S, Cao P, Chong MKC,Wang J, He D, Deng X and Ran J(2021) How Transportation RestrictionShapes the Relationship BetweenAmbient Nitrogen Dioxide andCOVID-19 Transmissibility: AnExploratory Analysis.Front. Public Health 9:697491 is available at
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