Analyzing the Contribution of Human Mobility to Changes in Air Pollutants: Insights from the COVID-19 Lockdown in Wuhan

Jiansheng Wu,Yuan Wang,Yun Qian,Na Wang

doi:10.3390/ijgi10120836

Abstract

During the COVID-19 lockdown in Wuhan, transportation, industrial production and other human activities declined significantly, as did the NO2 concentration. In order to assess the relative contributions of different factors to reductions in air pollutants, we implemented sensitivity experiments by Random Forest (RF) models, with the comparison of the contributions of meteorological conditions, human mobility, and emissions from industry and households between different periods. In addition, we conducted scenario analyses to suggest an appropriate limit for control of human mobility. Different mechanisms for air pollutants were shown in the pre-pandemic, pre-lockdown, lockdown, and post-pandemic periods. Wind speed and the Within-city Migration index, representing intra-city mobility intensity, were excluded from stepwise multiple linear models in the pre-lockdown and lockdown periods. The results of sensitivity experiments show that, in the COVID-19 lockdown period, 73.3% of the reduction can be attributed to decreased human mobility. In the post-pandemic period, meteorological conditions control about 42.2% of the decrease, and emissions from industry and households control 40.0%, while human mobility only contributes 17.8%. The results of the scenario analysis suggest that the priority of restriction should be given to human mobility within the city than other kinds of human mobility. The reduction in the NO2 concentration tends to be smaller when human mobility within the city decreases by more than 70%. A limit of less than 40% on the control of the human mobility can achieve a better effect, especially in cities with severe traffic pollution.

Highlights

In recent years, severe air pollution has killed many people, which has aroused concern [1]
During the lockdown period in 2020 (Table 3), the average pressure was the highest, and the average relative humidity was relatively low, which was unfavorable to the reduction in the NO2 concentration
During the pre-lockdown period, the temperature was relatively low, while during the lockdown period, the temperature was higher than that in the pre-pandemic period. Despite all those negative effects on reduction, the NO2 concentrations 2020 were lower than that in the pre-pandemic period, which reflected that road traffic dominated the reduction in the NO2 concentration during the lockdown period, while the meteorological conditions contributed the least

Summary

Introduction

Severe air pollution has killed many people, which has aroused concern [1]. The air pollution is a comprehensive result of meteorological conditions and human activities. Road traffic is deemed as an important source of NO2 and PM2.5 [2,3,4], and it has a significant impact on the concentration of O3. After the COVID-19 outbreak in Wuhan in December 2019 [5,6], China activated a first-level public health emergency response in Wuhan on 23 January 2020, taking measures such as cancelling mass gatherings, reducing the frequency of bus services in the city and halting long-distance buses [7]. The improvement in air quality emerged, as was reported that tropospheric NO2 vertical column densities reduced by 22–67% over

Methods

Results

Discussion

Conclusion