Air Quality During The COVID-19 Epidemic in China

doi:10.21203/rs.3.rs-1400011/v1

At the end of 2019, the COVID-19 emerged in Wuhan, China. It has since put global public health institutions on high alert. People reduced their traveling, and production has stopped nationwide during the epidemic. This paper explores the effect of these COVID-19-derived changes on the air quality in China. Air quality data of 367 cities around China were included. The daily air pollutants concentration (AQI,CO, O₃, NO₂, SO₂, PM10, and PM2.5) were collected. We compared the air quality changes between three periods (23.1.2019-23.3.2019, 22.11.2019-22.1.2020, and 23.1.2020–23.3.2020). To compare, we calculated the daily average number of cities with pollution, and the trend in air quality index change. Furthermore, Air quality in the top 50 cities with confirmed cases and Wuhan was analyzed. During the period between 23.1.2020 and 23.3.2020, the number of cities with excellent air quality was significantly higher than that in another two periods. The concentrations of PM2.5, PM10, NO₂, SO₂, CO, and O₃ decreased significantly during the COVID-19 epidemic. The most significant decreases were in PM10 and NO₂. The number of cities with good air quality in the later period was significantly higher than that a year before. The air quality has improved significantly during the COVID-19 outbreak, The reason for this change may be human activities such as reduced transportation and production stoppage.

COVID-19

AQI(Air Quality Index)

air pollutant

China

COVID-19 is a kind of pneumonia caused by a new type of coronavirus. It is a newly emerging infectious disease. It was reported very early in Wuhan, China [1]. Subsequently, the Chinese government promptly notified the World Health Organization of the actual situation in China. On January 20, 2020, Academician Zhong Nanshan, a member of the national high-level expert group, publicly introduced the characteristics of human-to-human transmission. After that, people took some protective measures, including restrictions on travel, isolation and wearing masks. At the same time, a new coronavirus was isolated and the gene sequence was published [2–4]. Because COVID-19 is extremely contagious, it spread all over the world in a short period of time. The World Health Organization declared it a pandemic on March 11, 2020. As of July 31, 2020, China has reported more than 88078 COVID-19 cases. It has infected more than 200 countries, with more than 100 million confirmed cases and 672509 confirmed deaths. In order to prevent the spread of the virus, various countries around the world have adopted blockade measures, requiring suspension of work and production, and home isolation[5]. On January 23, 2020, the day before the Spring Festival, the Chinese government completely blocked Wuhan and required all parts of the country to suspend work and production[6].

As an unprecedented blockade, many areas have experienced a dramatic reduction in air pollution. Between January 1 and March 11, 2020, NO₂ emissions in Barcelona (Spain) dropped significantly, which coincided with the lockdown period to fight the coronavirus[7]. In addition, the Institute of Environmental Science and Meteorology (IESM) estimates that since the implementation of Luzon’s enhanced community quarantine on March 16, 2020, Metro Manila’s PM2.5 and PM10 emissions have been significantly reduced due to the use of crushing and grinding machinery[8]. Reduced utilization and low dust exposure on the road. The air pollution index of India’s two major cities, Lucknow and New Delhi, has dropped significantly, and air quality has improved. The most influential ones are PM2.5, NO₂ and CO[9].

Air pollution will adversely affect human health and many ecosystem functions in the short and long term. This impact is most significant in developing countries and is considered an important risk factor for global morbidity and mortality[10, 11].A large number of studies conducted in the past few decades have shown that air pollution causes people to die from cardiovascular and respiratory diseases[12, 13]. In China, in recent years, air pollution has quickly become a central environmental problem. China is currently the largest developing country in the world. Since the "economic reform and opening up" in 1978, China's economy has developed rapidly. According to reports, the acute increase in air pollution in Beijing has significantly increased the number of hospitalizations during the acute exacerbation of chronic obstructive pulmonary disease (COPD)[14] .Due to the increase and aging of the Chinese population, the number of premature deaths related to PM2.5 is on the rise. [15].

Many air pollution studies have shown that human-related activities such as industrial production, traffic and transportation are the main factors causing air pollution[16–17]. During the 2008 Olympics and the 2016 Rio Olympics, the government took measures to require some companies to suspend work and production. Improve the air environment quality, but this time passively interfere with human activities[18–19]. During the COVID-19 period, extreme measures of complete or partial lockdown may almost stall these production and consumption activities. This background provides us with a unique opportunity to study the impact of human activities on air quality. At present, in response to the COVID-19 public health incident, it only provides information on the average air quality index (AQI) drop of 7.80% in 44 cities in northern China from January 1 to March 21, 2020, and 5 types of air pollutants (SO2, SO2). P2.5, M10, N2, and CO) decreased by 6.76%, 5.93%, 13.66%, respectively, to 24.67% and 4.58%, respectively[20]. Research has not been conducted on the national area to explore the impact of human activities on air pollution.

In this study, we are mainly based on 367 cities across the country, considering the air pollution situation before, during the closure period, and the same period of the closure period last year, comparing the air changes in the three periods, and then further comparing the number of people diagnosed during the epidemic. Changes in the air in the top 50 cities. Explore the impact of COVID-19 on the air environment, further explain the effect of appropriate reduction of human activities on improving the environment, and provide guiding measures for the harmonious coexistence of man and nature

Data sources

AQI and six pollutants(PM2.5, PM10, SO_2, O_3, NO2 and CO ) are commonly used to evaluate air quality. In this study, air pollution data from 367 urban monitoring points across China were included (Fig. 1). Data included daily values of PM2.5 (µg/m³), PM10 (µg/m³), SO₂ (µg/m³), O₃ (µg/m3), NO2 (µg/m3), CO (µg/m3), Mean temperature(℃), humidity(g/m³) and rainfall(millimeter). The pollution severity level was assigned based on the Air Quality Index (AQI). The AQI value runs from 0 to 500 and is divided into six categories as provided in Supplementary Table 1. All data were downloaded from the Zhen Qi Web database (https://www.zq12369.com/).

Inclusion time cycle

Because of the COVID-19, Wuhan began the city lockdown on January 23, 2020. Travel restrictions, the requirement for the work stoppage, and home confinement were enacted throughout the country. On March 23, 2020, the government began permitting all regions of the country to return to work. These dates defined the epidemic period(23.1.2020—3.23.2020). The two preceding months(11.22.2019—3.22.2020) and the parallel two months of the previous year (23.1.2019-3.23.2019) constituted the other two periods. On April 8, 2020, the Wuhan Government announced the lift of the closure. We thus chose for Wuhan slightly different time slots: 23.1.2019—8.4.2019, 7.11.2019—22.1.2020, and 23.1.2020—8.4.2020.

Statistical analysis

The difference between different periods is measured by the average daily pollution level of each cycle. To calculate the average air pollution level of each cycle, for example (23.1.2020—3.23.2020), the average level of PM2.5 is equal to the sum of each day in the cycle divided by the total number of days in the cycle. First of all, we compare the difference of pollution in the whole country and the specific situation of Wuhan. The daily average number of polluted cities in three periods was compared. Using time series analysis method, the changes of PM2.5, PM10, SO2, O3, NO2, CO, average temperature, moderation and rainfall were discussed. The changes of pollution levels in the top 50 cities and Wuhan during the epidemic period were compared in three cycles. T-test was used to evaluate the difference of each factor. The significant level was p < 0.05. All analyses were performed using statistical programming environment R (version 3.6.0).

The average level of air pollution index decreased and the level distribution had significant difference (P < 0.05). During the periods of 23.1.2019-23.3.2019 and 23.1.2020-23.3.2020, AQI decreases by 13.2, PM2.5 decreases by 12.4, PM10 decreases by 20.8, SO₂ decreases by 2.9, NO₂ decreases by 9.4, CO decreases by 0.2, and O₃ decreases by 17.1. During 22.11.2019-22.1.2020 and 23.1.2020-23.3.2020, AQI decreases by 13.6 and PM2.5 decreases by 15.4, PM10 decreased by 16.0, SO₂ by 3.3, NO₂ by 17.1, CO by 0.3 and O₃ by 12.7. There was no significant difference in mean temperature, humidity and rainball levels between 23.1.2019-23.3.2019 and 23.1.2020-23.3.2020 (P > 0.05)(Table1)

The distribution of AQI levels of polluted cities in China every day in the three cycles included is shown in Figure 2. It can be clearly seen that in the period of 23.1.2020-23.3.2020, the number of Good cities is significantly more than that of 23.1.2019-23.3.2019 and 22.11.2019-22.1.2020. There is no significant difference in the number of cities in moderate. The number of cities that were Slightly, Modestly and Heavily polled was the least in the period of 23.1.2020-23.3.2020. In the period of 23.1.2020-23.3.2020, the number of cities that are Extremely polled is 0。

We found that the daily average concentration curves of PM2.5, PM10, NO₂, SO₂, CO, and O₃ during the last period were all lower than those in the earlier two periods(Figure 3).For Wuhan, the AQI during 23.1.2020-8.4.2020 was significantly lower than that during 23.1.2019-8.4.2019. The number of days with good air quality in the later period was significantly higher than that a year before. The number of days defined as ‘Slightly polluted’ during the period from 7.11.2019 to 22.1.2020 was significantly higher than that between 23.1.2020 and 8.4.2020 (Figure 4). We further analyzed the changes of air levels in the top 50 cities (see Supplementary figure1 for the number of confirmed cases) during the epidemic period, and found that PM2.5, PM10, SO₂, NO₂, CO and O₃ were all lower than 23.1.2019-23.3.2019 and 22.11.2019-22.1.2020 cycles in these cities (Figure 5).

In this study, based on the air quality data of 367 cities in China, the changes of air quality in three periods were compared. It is clear that during the epidemic period, the air quality of the whole country has been significantly improved. In the 50 cities with the first confirmed cases, PM2.5, PM10, SO₂, O₃, NO₂ and co decreased significantly. Although this study is only a preliminary study of the changes in air quality during the outbreak, we can clearly see the environmental changes affected by human activities, and provide preliminary guidance for improving the environment.

Previous studies have evaluated the level of air pollution and its impact on public health, finding it to increase the incidence of respiratory, heart, and nervous system diseases, among others.^[21,22,23] In addition, during the outbreak of COVID-19, "Nature" reported a decrease in human activity, and the seismic waves also decreased accordingly.^[24] However, the study on the impact of air quality was only based on 44 urban areas in the north, and the results showed that air quality improved during the outbreak. In this study, we compared two months of confinement with the previous two months and the same period of the previous year, based on 367 regions across the country. We found that during the period of confinement, air quality across the country has improved significantly. This is the first time that human beings stop production passively due to the outbreak of epidemic, and the research has a strong representative.

Reducing human manufacturing activities can improve air quality. A typical manifestation of humans’ initiative to improve environmental quality is to take active measures to control the pollution, including controlling the number of vehicles and strictly restricting factory production activities. These measures can significantly improve air quality, and thus reduce hospital visits due to related diseases.^[18,19]

The COVID-19 epidemic that broke out at the end of 2019 has completely changed the rhythm of people's lives and production.^[25] After confirming that the disease can be transmitted between people,^[26] the Chinese government took measures to close the city of Wuhan, mobilize Chinese medical personnel to help fight against the SARS-CoV-2,^[27] restrict human travel,^[28] establish sheltered hospitals,^[29] forcefully instructed the population to wear masks,^[30] and designated hospitals to treat pneumonia patients. These comprehensive measures have effectively contained the epidemic in China by mid-March, 2020.

From another perspective, Amongst other impacts, the COVID-19 epidemic, and the passive production stoppage and the traffic control and shutdown due to it, have impacted the environmental quality. This improved air quality reflects the people's initiative to reduce travel frequency and stop production, and proves that such behavioral changes can improve the environment.

However, this improvement in air quality will only be a temporary one. If we want to maintain cleaner air for a longer time, we have to turn to clean energy and transportation, rather than order people to stay at home at the expense of huge economic losses. But during the COVID-19 pandemic, the clear sky also told us that improving the natural environment, human beings should stop their activities and production appropriately, instead of developing natural resources to satisfy human beings indefinitely.

Human production or consumption activities will lead to increased air pollution. In response to the impact of COVID-19, China's unprecedented blockade has brought almost all such activities to a standstill. Measures such as closing industrial factories and suspending urban traffic may change the distribution of air pollutants in cities. The exogenous impact of the epidemic reflects that people can better improve the environment by actively reducing travel frequency and stopping production.

Funding

This study was supported by Hangzhou Science and Technology Bureau fund (No. 20191203B96; No. 20191203B105;No. 20191231Y039); Youth Fund of Zhejiang Academy of Medical Sciences (No. 2019Y009); Medical and Technology Project of Zhejiang Province (No. 2020362651, No.2021KY890); Clinical Research Fund of Zhejiang Medical Association (No. 2020ZYC-A13); Hangzhou Health and Family Planning Technology Plan Key Projects (No.2017ZD02). Hangzhou Medical and Health Technology Project (No. 0020290592). Zhejiang Traditional Chinese Medicine Scientific Research Fund Project(No.2022ZB280).

Conﬂict of interest

All authors declared no conﬂict of interest pertaining to this work

Acknowledgement

The work was supported by the Key medical disciplines of Hangzhou and pre-research fund project of Affiliated Hospital of Hangzhou Normal University.

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Table1 Mean concentrations and standard deviations of PM2.5, PM10, NO₂, SO₂, CO, and O₃ (μg m⁻³) during the three studied periods in China

	23.1.2019—23.3.2019		22.11.2019—22.1.2020	23.1.2020—23.3.2020	Change1*	Change2*	p_value1*	p_value2*
AQI	80.6±16.1	81.0±15.9		67.4±10.9	13.2	13.6	<0.05	<0.05
PM2.5	52.4±15.0	55.4±13.8		40±11.6	12.4	15.4	<0.05	<0.05
PM10	85.2±17.7	80.4±15.7		64.4±12.5	20.8	16.0	<0.05	<0.05
SO₂	13.4±2.6	13.8±3.2		10.5±1.5	2.9	3.3	<0.05	<0.05
NO₂	29.4±7.8	37.1±7.7		20.0±4.6	9.4	17.1	<0.05	<0.05
CO	0.9±0.16	1.0±0.2		0.7±0.1	0.2	0.3	<0.05	<0.05
O₃	81.8±9.8	77.4±12.0		64.7±10.5	17.1	12.7	0.03	<0.05
Mean temperature	5.6±3.4	3.3±2.1		6.2±3.6	-0.6	-2.9	0.13	<0.05
humidity	63.3±6.0	69.4±6.5		64.5±7.7	-1.2	4.9	0.35	0.02
rainfall	1.4±1.1	1.0±0.8		1.4±1.0	0.0	-0.4	0.95	0.03

* Change1: Level in cycle 23.1.2019—23.3.2019 - level in cycle 23.1.2020—23.3.2020 *Change2: Level in cycle 22.11.2019—22.1.2020 - level in cycle 23.1.2020—23.3.2020 *p_value1: Level statistical difference between 23.1.2019—23.3.2019 and 23.1.2020—23.3.2020

*p_value2: Level statistical difference between 22.11.2019—22.1.2020 and 23.1.2020—23.3.2020

SupplementaryTable1.docx
Supplementaryfigure1.tif
Supplementary figure 1: The number of confirmed cases in the top 50 cities

Air Quality During The COVID-19 Epidemic in China

Status:

Version 1

Abstract

Figures

1. Introduction

2. Methods

3. Results

4. Discussion

5. Conclusion

Declarations

References

Tables

Supplementary Files

Status:

Version 1