key: cord-0886291-gbs19egg
authors: Lian, x.; Huang, J.; Zhang, l.; Liu, c.
title: Environmental indicator for effective control of COVID-19 spreading
date: 2020-05-16
journal: nan
DOI: 10.1101/2020.05.12.20099804
sha: b4f7a28da850040c4930481c3e9b66fd9916c161
doc_id: 886291
cord_uid: gbs19egg

Recently, a novel coronavirus (COVID-19) has caused viral pneumonia worldwide, spreading to more than 200 countries, posing a major threat to international health. To prevent the spread of COVID-19, in this study, we report that the city lockdown measure was an effective way to reduce the number of new cases, and the nitrogen dioxide (NO2) concentration can be adopted as an environmental lockdown indicator. In China, after strict city lockdown, the average NO2 concentration decreased 55.7% (95% confidence interval (CI): 51.5-59.6%) and the total number of confirmed new cases decreased significantly. We also determined that the global airborne NO2 concentration steeply decreased over the vast majority of COVID-19-hit areas based on satellite measurements. We found that if NO2 emissions significantly decreased, the total number of confirmed new cases reached an inflection point after approximately two weeks. Italy, Germany and France are good examples. Our results suggest that NO2 satellite measurement can help decision makers effectively monitor control regulations to reduce the spread of COVID-19.

Large-scale COVID-19 viral pneumonia through human-to-human transmission poses a 35 severe and acute public health emergency 1, 2 . As the epidemic worsened, most countries imposed 36 city lockdown and quarantine measures to reduce transmission to control the epidemic. The 37

Chinese government has gradually implemented a city-wide quarantine of Wuhan and several 38 surrounding cities as of 23 January, flights and trains to and from Wuhan have been suspended, 39 and public transport has been halted 3,4 . The entire northern Italy was quarantined since 9 March 40 2020, and three days later the government extended it to the whole country 5 .The Spanish 41 government declared a 15-day national emergency, starting on 15 March 6 . In the United States, 42 on 19 March, California became the first state to order a lockdown 7 . In Germany, since 18 March, 43 16 states have closed, public gatherings of more than two people have been banned and most 44 shops except supermarkets and pharmacies have closed 8 . On 23 March, the British government 45 announced a new nationwide restriction allowing residents to only venture outside when 46 absolutely necessary, e.g., to work, buy necessities 9 . 47

The worldwide lockdown, which was imposed to stop the spread of the novel coronavirus, 48 not only caused an economic downturn but also appeared to result in cleaner air in urban areas 49 usually heavily affected by pollution 10 . The most important measure of the lockdown policy was 50 the reduction of traffic and control personnel flow, and traffic pollution is an important factor 51 influencing air quality and public health. Vehicle exhaust and evaporation emissions are the main 52 emission sources of ozone and secondary particle precursors near the ground in cities and 53 regions 11 , and the spatial variation of nitrogen dioxide (NO 2 ), fine particulate matter (PM 2.5 ) and 54 black carbon (BC) may also be significant affected by traffic flow density 12 

Angeles showed that nitrogen oxides (NO x ) were identified as a source of pollution for light 56 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted May 16, 2020. . https://doi.org/10.1101/2020.05.12.20099804 doi: medRxiv preprint vehicles, with NO 2 , NO x , carbon dioxide (CO 2 ), BC, and fine particle number (PN fine ) identified 57 as diesel exhaust sources 13 . In South Korea, source analysis studies have shown that there is a 58 high correlation between estimated traffic volume and NO 2 concentration 14 . In Britain, road 59 transport accounts for 80% of the NO x emissions 15 . NO 2 levels can be used as a proxy for 60 exposure to traffic-related composite air pollution and to assess the impact of scenarios designed 61 to reduce traffic-related emissions 16,17 . 62 In this report, we study the parameters of environmental indicators for city lockdown. Using 63 the automatic ground detection data and satellite data to analyze the trend of lockdown and the 64 total confirmed new cases in major cities in China, and using satellite data to further study the 65 impact of lockdown on virus transmission in countries mainly severely affected by the epidemic, 66 in order to help policymakers to formulate effective control measures to reduce the spread of 67 COVID-19. 68 69

The ground observation daily data were provided by the China National Environmental 71

Monitoring Centre (http://www.cnemc.cn/). The data from January 24, 2020, to February 23, 72 2020, are selected as the representative data after the lockdown in Hubei, and the data from 73

December 24, 2019, to January 23, 2020, are selected as the representative data before the 74 lockdown ( Figure 1 ). The NO 2 ground observation data of China is from 1 January 2020 to 1 75

March 2020. The average concentration of major cities with severe epidemic diseases was 76 selected as the representative of NO 2 concentration of China, including Wuhan, Nanchang, 77

Guangzhou, Hangzhou, Changsha, Beijing, Shanghai, Hefei and Zhengzhou (Fig. 3) . All 78 monitoring instruments of the air quality automatic monitoring system operate automatically 24 79 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted May 16, 2020. 

where VA is the relative variation ratio, N1 is the average NO 2 concentration in the 99 troposphere one month before the lockdown, and N 2 is the average NO 2 concentration in the 100 troposphere one month after the lockdown. 101 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted May 16, 2020. the closure of major cities severely affected by the epidemic. Compared with before the 120 lockdown, NO 2 , SO 2 , PM 10 , CO and PM 2.5 concentrations all decreased to a certain extent, while 121 NO 2 experienced the most notable decrease (Figure 1 ). Since biomass and coal combustion are 122 major SO 2 and CO sources, they exhibit the lowest rate of improvement 18, 19 . Both the PM 2.5 and 123 PM 10 concentrations decreased to a certain extent (31.2% and 34.3%, respectively) as a result of 124 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted May 16, 2020. . https://doi.org/10.1101/2020.05.12.20099804 doi: medRxiv preprint the reduction in fugitive dust, particulate matter and important precursors produced by motor 125 vehicles and factories 20 . The monthly average PM 2.5 /PM 10 ratio was 0.81 (95% confidence 126 interval (CI): 0.76-0.86), so PM 2.5 was the main particle pollutant after lockdown. Exhaust 127 emissions contributed only moderately to local levels of the PM 2.5 total mass, which were mostly 128 derived from other sources, such as biomass combustion and the remote transmission of 129 secondary particles. Therefore, the impact of strict traffic control during the lockdown on PM 2.5 130 is not notable, and the spatial difference is large, so PM 2.5 is not suitable as a city lockdown 131 indicator. 132

Although the NO 2 emissions per vehicle slightly decreased after the upgrading of the 133 quality standards of petroleum products, the notable growth of vehicle ownership increased the 134 proportion of NO 2 traffic source emissions, in addition, after the implementation of emission 135 standards for coal-fired power plants, multiple technical improvements greatly controlled the 136 NO 2 emissions from coal-fired sources, which all enhanced the correlation between NO 2 and city 137 lockdown effect 21 . The effect of city closure on NO 2 was significantly greater than that on the 138 other pollutants, with an average concentration reduction of approximately 60.3% (95% CI: 139 56.8-64.0%), which can be applied as an environmental indicator of the lockdown effect. 140

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The copyright holder for this preprint this version posted May 16, 2020. The national emergency response has delayed the spread of the epidemic and greatly limited 187 its range. The suspension of intra-city public transport, the closure of entertainment venues and 188 the banning of public gatherings have been linked to a reduction in the incidence of cases. 189

Studies have shown that before emergency response initiation, the (basic) case reproduction 190 number (R 0 ) is 3.15, and after intervention measures were implemented in 95% of all places, the 191 average R 0 value has dropped to 0.04, the total number of actual cases has decreased 96% 27 . 192 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted May 16, 2020. China, especially in the strictly controlled cities. In many European countries, a strict lockdown 231 is also effective and easy to do to prevent the spread of the virus. But there are also areas such as 232 southern and northern Spain and parts of the United States where the NO 2 level has increased. 233

Studies have shown that the likelihood of fewer cases in the gradual multi-stage policy is 234 zero, and that such a policy decision implies that the government is willing to risk an increase in 235 COVID19 cases and deaths in exchange for decreased economic and isolation impacts, which 236 may not be desirable from an objective point of view 29 . Although the immediate adoption of a 237 lockdown policy may lead to many people being adversely affected financially, in the short term, 238 the number of new confirmed cases will decline approximately 15 days after policy 239 implementation, and an earlier decline can occur with stricter lockdown measures. International 240 guidance supports a range of mandatory social isolation measures, extensive case detection, and 241 isolation and contact tracing 9 . Compliance with quarantine directives is absolutely critical to 242 saving lives, protecting the most vulnerable in society, and ensuring that the national security 243 system can cope and care for the sick. In such cases, an immediate lockdown policy may be 244 preferred, and NO 2 , as an environmental indicator of virus control, can help managers implement 245 effective control measured to curb the spread of COVID-19. 246

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The copyright holder for this preprint this version posted May 16, 2020. . https://doi.org/10.1101/2020.05.12.20099804 doi: medRxiv preprint . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted May 16, 2020. . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted May 16, 2020. interpretation and manuscript writing. X. L. L.Z. and W.L. contributed to the data analysis, 349 interpretation and manuscript writing. All of the authors contributed to the data analysis, 350 discussion and interpretation of the manuscript. All of the authors reviewed the manuscript. 351 352

Additional information 353

Competing financial interests: The authors declare no competing financial interests. 354 355

Graphics software 356

All maps and plots were produced using license. 357

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The copyright holder for this preprint this version posted May 16, 2020. . https://doi.org/10.1101/2020.05.12.20099804 doi: medRxiv preprint

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