Effect of COVID-19 on transportation air pollution by moderation and mediation analysis in Queens, New York

The outbreak of the COVID-19 virus in 2020 has left many changes in the quality of life and environment, including air quality in different parts of the world. As a result of lockdown conditions, the level of air pollution has been changed considerably due to topographic, geographical, and cultural conditions as well as traffic restrictions. Thus, this study aimed to investigate the effect COVID-19 outbreak on improving air quality as a result of changes in traffic volume and traffic patterns in Queens, New York, using the moderation and mediation analysis model structure. In this model, COVID-19 outbreak periods were defined as a moderating variable, traffic volume (number of daily vehicles) as an independent variable and mediator, and air pollution concentration parameters (NO(x), PM(2.5), and O(3)) individually as dependent variables. Three-time periods were selected, each representing the duration and severity of traffic restrictions and prohibitions, and these three periods corresponded to 1 February–4 March, 5 March–21 March, and 22 March–15 May. They represented the normal, aware, and lockdown periods, respectively. The result of the study showed that in 2020 compared to the last five consecutive years, PM(2.5) and NO(x) pollutants decreased by 39.2% and 35.8% as a result of the traffic ban due to the COVID-19, but an increase of 15.1% in O(3) pollutant was observed in the mentioned period. Although traffic restrictions reduced total traffic volume compared to the same period last year, there has been no significant reduction in the air quality index (AQI). The reduction in NO(x) concentration leads to more O(3) ground levels, and this caused the AQI not to decrease significantly. Finally, the moderation and mediation model results showed that the COVID-19 almost has no significant effect on the correlation between daily traffic and the concentration of NO(x), PM(2.5), and O(3) pollutants as moderator. However, the COVID-19 has a significant correlation with O(3) and PM(2.5) concentration, and the traffic volume mediation effect is negligible. Therefore, the statistical analysis and models show that the COVID-19 pandemic is an effective traffic volume and air quality parameter.