COVID-2019 lockdown in Beijing: A rare opportunity to analyze the contribution rate of road traffic to air pollutants

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Yalu Xin

aChina Academy of Building Research, Beijing, 100013, China

bState Key Laboratory of Building Safety and Built Environment, Beijing, 100013, China

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Shuangquan Shao

cSchool of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China

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Zhichao Wang

aChina Academy of Building Research, Beijing, 100013, China

bState Key Laboratory of Building Safety and Built Environment, Beijing, 100013, China

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Zhaowei Xu

aChina Academy of Building Research, Beijing, 100013, China

bState Key Laboratory of Building Safety and Built Environment, Beijing, 100013, China

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Hao Li

aChina Academy of Building Research, Beijing, 100013, China

bState Key Laboratory of Building Safety and Built Environment, Beijing, 100013, China

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Author information Article notes Copyright and License information Disclaimer

aChina Academy of Building Research, Beijing, 100013, China

bState Key Laboratory of Building Safety and Built Environment, Beijing, 100013, China

cSchool of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China

⁎Corresponding author at: 30#, Bei San Huan Dong Lu, Chaoyang District, 100013, Beijing, China.

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Abstract

In Beijing, the lockdown imposed to curb the spread of COVID-2019 has led to a sharp drop in road traffic. This provides an opportunity to quantify the contribution rate of road traffic to PM2.5 and NO2 concentrations. This paper creatively puts forward the concept of the Maximum Possible Contribution Rate (MPCR) and estimates the MPCR of road traffic to PM2.5 and NO2 by analyzing the daily air pollution data and road traffic data in Beijing from January 24 to March 31, 2020 and the same period in 2019. The findings of this paper include: The decrease in SO2 concentration during the lockdown indicates a reduction in pollutant emissions from industry and households. During the lockdown, road traffic in Beijing reduced by 46.9 %, while the concentrations of PM2.5 and NO2 in the atmosphere reduced by 5.6 % and 29.2 % respectively. The MPCR of road traffic to PM2.5 and NO2 concentrations are 11.9 % and 62.3 %, respectively. The concentration of O3 did not increase significantly with the decrease of PM2.5 and NO2 concentrations. The findings of this paper provide a reference for city managers to evaluate the contribution rate of Beijing’s road traffic to air pollutants and to formulate reasonable emission reduction policies.

Keywords:

COVID-2019, Lockdown, Road traffic, MPCR, PM2.5, NO2

5. Discussion

According to the research results in Section 4.2, the contribution rate of road traffic to PM2.5 and NO2 in Beijing will not exceed 11.9 % and 62.3 %. Road traffic is the most important pollution source of NO2, but not the most important pollution source of PM2.5. Some studies have found that road traffic emissions account for 10 %–20 % of total PM2.5 emissions of the city (Huang, Zhang, & Bozzetti, 2014; Li, Zhang, & Zhang, 2015; Yang, Chen, & Wen, 2016). This is consistent with the MPCR of Beijing road traffic to PM2.5 obtained in this paper. In addition, some studies have found that the contribution rate of road traffic to NO2 is about 50 % (Frey, Zhang, & Rouphail, 2010; Shon, Kim, & Song, 2011), which is also close to the MPCR of Beijing traffic to NO2 obtained in this paper. This shows that the conclusions drawn in this paper are reasonable.

In this paper’s research findings, the O3 concentration in Beijing increased during the lockdown and the same phenomenon also appeared in other cities that implemented the lockdown. This may be related to the reduction of PM and NOx concentration (Laurent et al., 2020; Pierre et al., 2020). The concentration of O3 did not increase significantly may be caused by the following reasons: (1) there was more rain and snow during lockdown, and the cleansing effect of rain and snow would reduce the O3 concentration in the atmosphere; (2) during the lockdown, the CO concentration dropped by 9.1 % compared with the same period in the previous year’s ( ). As one of the important precursors of O3, the decrease of CO concentration will inhibit the production of O3.

6. Conclusion

This article creatively puts forward the concept of MPCR. When a major change occurs in a pollution source, if other influencing factors have a positive impact on a pollutant, the change in the concentration of this pollutant can be regarded as having been completely caused by this pollution source. The MPCR of this pollution source to the pollutant can be obtained. Using this method and taking advantage of the rapid decline in the number of road traffic in Beijing during the lockdown, this paper studied the MPCR of Beijing’s road traffic on PM2.5 and NO2.

In order to minimize the impact on climatic conditions, this paper chose to compare the concentration of atmospheric pollutants during the lockdown with the same period in 2019. However, the climatic conditions in both years were not exactly the same. Compared with the same period in 2019, the weather conditions in 2020 were more conducive to reducing the concentration of pollutants in the atmosphere. In addition, during the lockdown, the SO2 concentration dropped by 37.4 %. Through the analysis of pollution sources, it is inferred that the pollutants discharged into the atmosphere by industry and households during the lockdown have been reduced.

During the lockdown period of this study, travel intensity in Beijing was reduced by 46.9 %, while the PM2.5 concentration and NO2 concentration in the atmosphere were reduced by 5.6 % and 29.2 %, respectively. When it is assumed that the decrease of PM2.5 and NO2 concentrations is caused entirely by the decrease of road traffic, the MPCR of road traffic to PM2.5 and NO2 concentrations is 11.9 % and 62.3 %, respectively. Road traffic is the most important pollution source of NO2, but not the most important pollution source of PM2.5.

In addition, this paper also found that although the concentration of PM and NOx decreased significantly during the lockdown, the concentration of O3 only increased by 1.0 %. Therefore, reducing the concentration of PM and NOx does not necessarily cause a substantial increase in the O3 concentration, but it also depends on the weather conditions and changes in the concentration of O3 precursors.

The research results of this paper provide an important reference for Beijing to formulate reasonable emission reduction policies. At the same time, the research method adopted in this paper has good versatility and is suitable for carrying out research on the contribution rate of pollutants in different cities. It greatly simplifies the calculation process, and can prevent cities from overestimating the impact of a certain pollution source in the process of formulate emission reduction policies.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.