Diagnostic Comparison of Changes in Air Quality over China before and during the COVID-19 Pandemic

The rapid spread of Covid-19 has affected the political, social, and economic sectors, which inevitably will also affect the environmental component. This contagious virus led the worldwide countries to make securities measures such as lockdown to reduce the spread of COVID-19 and protect human health. In contrast to the negative impacts of this virus on the economy, it has inuenced the environment positively. As reported by station and program for monitoring the Earth, the air quality has improved after the lockdown. The present study compares the air level pollution one year before and during the spread of Coronavirus in China. Accordingly, we investigate the change of the concentrations of three air pollutants, namely, O 3 , NO 2 , and black carbon. The study of the measured parameter between December 2019 and March 2020 exhibit an apparent decrease in their concentrations because of the imposing lockdown of cities and restriction on chemical industries and factories.


Introductions
Incipient viruses are getting a challenge for people all around the world. Corona viruses are among them.
These viruses affect humans, including other mammals and birds. The fast spreading of the COVID-19 cases has created a worldwide pandemic and brought lethal consequences .
Coronaviruses are very infectious, cause tract diseases that will be lethal. Mild symptoms of corona include respiratory illness, cough, fever, etc., and can cause multiple organ failure and result in death.
Four kinds of common coronavirus that causes infections in humans are 229E, NL63, OC43, and HKU1.
Most of the people globally can develop a minimum of one amongst these over their lifetime. Three other coronaviruses emerged in animals and transmitted to humans and produced critical risks to human health. They are described as SARS-CoV, MERS-CoV, SARS-CoV-2. In step with the WHO, the rst human cases of SARS-CoV were observed in southern China in November 2002. Previous studies revealed that SARS-CoV might have originated in bats then transmitted to other animals before infecting humans.
According to the study done by WHO, MERS-CoV, has rstly appeared in September 2012 in an Asian country and it spread through the close contact of humans with camels as well as through human-tohuman contact.
In late December 2019, a replacement coronavirus has appeared in Wuhan, Hubei Province, China i.e., SARS-CoV-2 causes COVID-19. The health administrators in Wuhan have observed a mass of cases of pneumonia, and the cause was linked to seafood and wet animals wholesale market situated in Wuhan city. It was also believed that the Wet market of Wuhan might not be the sole source of coronavirus. A recent study conducted by Società Italiana di Medicina Ambientale (SIMA) has indicated that the speci city of the important rate spread of the coronavirus in some zones of Northern Italy is seem related to air pollutions conditions (Martelletti & Martelletti, 2020).
On December 31, 2019, the Chinese Center for Disease Control and Prevention (China CDC) sent off a team to Wuhan to conduct an investigation, they doled out it and recorded the obtained results. They found the source of the pneumonia masses in patients and they detected the novel coronavirus in patients whose specimens were tested by the CDC. Prior, it was suggested that the patients who suffered by pneumonia and transmitted this virus may have visited the wet animal or seafood market where the animals sort of a bat, snakes, birds, etc., However, after this investigation, the researchers unveiled that some individuals infected with this virus do not show any record of a visit to the present wet or seafood market. Furthermore, this research revealed the human-to-human transmission capability of this new virus, which is caused by the close contact with an infected person liable to coughing, respiratory droplets of aerosols, or sneezing. These respiratory droplets enter the physical body by inhalation through the nose or mouth and then contaminating no infected persons. This virus belongs to the β group of coronaviruses. The Chinese Researchers named this virus as Wuhan coronavirus or 2019 novel coronavirus (2019-nCov). Around 210 countries and territories are affecting by COVID-19. The source of SARS-CoV-2 is not con rmed, but it is believed that it arose from bats.
In early January, the pandemic began to increase rapidly in many cases. It has affected the political, social, and economic sectors, which inevitably will also in uence the environment. January 24, 2020, numerous countries have also reported the patients plagued by the same virus, which means that this virus exported to other countries via infected individuals coming from China. After that, the number of cases infected with COVID-19 continued to grow up to date, and the number of deaths caused by this virus exceeds the death amount caused by other types of coronaviruses. The number of con rmed cases crossed the mark of 1.5 million globally. Until now, no speci c treatments exist to cure or vaccine to cater to COVID-19. However, symptoms will be treated in clinical conditions. In step with observations, the recovery time for patients varies from 2 weeks to 3-6 weeks in severe cases. People infected with COVID-19 generally develop symptoms, including respiratory signs and fever, on a median of 5-6 days after infection and during a period of 1 to 14 days. Symptoms and signs shown by patients are dry cough, fever and tiredness. Some patients also develop chest congestion, aches, and pains, diarrhea, runny nose and in ammatory disease.
As of April 14, the WHO has been reported 19, 20,918 con rmed cases and 1, 19,686 death cases worldwide (Table 1; Fig.1). Currently, every nation is trying to regulate and limit the transmission of SARS-CoV-2 in humans. On a global level, lockdown is adopted to prevent the public gathering, keep people at their homes and keep them aloof from their o ces, public transports, etc.. In order to keep up social distancing, various other methods were adopted. In turn, the USA, Italy, Spain, China have been almost coms to rest. Streets, Malls, theatres, etc. are deserted, aircraft grounded, travel restricted. Factories shut down, events canceled and postponed, and all activities were blocked.
COVID-19 has dramatically impacted the world economy, the petrol barrel price has shut down and recently the benchmark US oil prices fell below zero for the rst time in the whole history of the oil market. The coronavirus crisis is the leading cause that has pushed demand for oil after the airlines reduced services, and travel restrictions lowered the amount of petrol pump activity. Besides, the petrol stations are now selling less fuel because of the containment, which dropped off the human consumption rate.
The mining activities around the world were also closed because of coronavirus, which caused an increasing trend of metals prices. The tourism activities were also postponed in the whole world in order to stop the virus spread.
These all activities generate every day high amount of pollutants in air, land and rivers, which reach easily ocean. The temporary suspend of these activities may have impacted positively the air quality. In order to understand how the economic impacts of Covid-19 have in uenced the environment a diagnostic comparison between the air quality before and after Covid-19 is needed. Currently, numerous studies are undergoing to investigate the effect of con nement on environment, which could be helpful to standard individuals and partially offset the costs of these counter-COVID-19 measures. As an example, satellite pictures caught a pointy decision in pollution in many countries that have taken aggressive measures on the transmission of the virus. Since a long time air pollution is affecting each and every part of the world. It is one of the biggest environmental and health problems worldwide. It could be a risk factor leading to death due to heart disease, attacks, respiratory infections, lung cancer, diabetes, and chronic pulmonary disease.

Study area
In this study, we focus on studying air quality in China before and after coronavirus. China is an east-Asian country, positioned north of the equator between 18°N and 54°N latitudes and 73°E and 135°E longitudes (Fig.2). The geo-coordinates of the country lie at 21°N and 78°E. China is the most populous country in the world, with over 1.428 billion in 2017. Across this large geographical scales and varying topography, the climate of the country is easily generalized, comprising a wide range of weather conditions. China's climate is generally dominated by dry seasons and wet monsoons, which cause pronounced temperature differences between the two seasons, winter and summer. Moreover, most of the regions in the country are having starkly different microclimates. Regional difference in the climatic condition of the country is due to its highly complex topography. Asian countries remain disproportionately affected by toxic air and so-called pollution-related problems in consideration with a large population, crowded cities, industrial emissions, etc. Ways adopted for the rapid economic development in the country has led to severe air pollution. The main cause of air pollution in the country is due to the seriousness of pollution, especially in the metropolitan cities throughout the county.

Methodology
Ozone Monitoring Instrument (OMI) is a Dutch Finnish ozone monitoring image spectrometer ( Table 2).
The instrument is designated for distinguishing ozone and other atmospheric species. OMI sensor has a spectral region of 264 -504 nm, a spectral resolution of 0.  For the study of total column ozone, the TOMS-like OMTO3e product has been used. It selects the best pixel data from the good quality level-2 total column ozone data (OMTO3). This product data falls in the 0.25 x 0.25-degree global grids. For the study of the tropospheric column, NO2OMNO2d data product has been selected. It is a Level-3 Gridded Product where pixel-level data of good quality are falling into 0.25x0.25 degree global grids. This product contains Tropospheric Column NO2, for all atmospheric conditions, with less than 30 percent cloud fraction. Black Carbon is one of the primary constituent components of atmospheric aerosols. Black carbon aerosols are highly absorbing and an essential factor in radiative forcing and radiative transfer. For the study of Black carbon, the M2TMNXAER product has been selected.
Monthly averaged data from January to March are used for the study from the years 2019 and 2020.
During the processing and the interpretation of satellite data, the GIS tool has been used primarily for mapping and for managing the geographical data information in a database. High-level languages are used for analyzing and visualizing the satellite-derived data products for the study. MATLAB and ORIGIN software has been used for numerical computation of the data.

Results And Discussion
Three parameters in uencing parameters namely; the ozone (O 3 ), the Nitrogen Dioxide (NO 2 ) and Black Carbon have harmful impacts on environmental safety due to their toxic effect on fauna and ora. In this context, it seems important to study their variation before and after the spread of Corona virus and to predict the main relation between their concentrations and the spread of Corona virus . A comparative study of the obtained rates before and after the spread of corona virus was reported.

Ozone (O 3 )
Ozone is a gas made up of 3 atoms of oxygen. It occurs naturally in the uppermost layer of the atmosphere, i.e., stratosphere and at ground level due to chemical reactions. Ozone is formed in a lower atmosphere near the earth's surface by the reaction of air pollutants released from vehicles, industries, chemical plants, and from other sources. These air pollutants react chemically in the presence of sunlight and form ozone. Stratospheric ozone is good as it protects us from the harmful ultraviolet radiation coming from the sun. It forms a protective layer that acts as a barrier against UV rays of the sun. Exposure of UV radiation can cause skin allergy, irritation in eyes, skin cancer, etc.
Conversely, the ozone layer which is present at ground level is very harmful to us. It acts as an air pollutant because of its adverse effects on humans and the environment. The life of individuals most at risk from inhaling air containing harmful ozone includes individuals who have asthma, workers, older children who are active outdoors. In addition, ground-level ozone affects ecosystems and vegetation, including forests, grasslands, and parks, including wildlife and wilderness areas.
The O 3 level change measured in china from December 2019 to March 2020 is illustrated was studied. lockdown with the mean concentration of last year ( Fig.4; table 3) reveals that the mean concentration of ozone is less important during the lockdown, which is certainly due to the decline of human-made emissions. Whereas, the variation of ozone reached about 11% in January 2020 because of the severe restrictions imposed by China in this month. In contrast, this percentage has decreased and reached 6% in February and 3% in March 2020. Some factories were resumed in the late February and March.

Nitrogen Dioxide (NO 2 )
Nitrogen dioxide is one of a component of a bunch of gaseous air pollutants. It is produced by various human activities like tra c, combustion of nitrogen-containing fuels, and many more.

Black Carbon
Black Carbon is a chemical component, released from diesel engines and gas mainly. It is formed by the process of incomplete combustion of fossil fuel, biomass and biofuels. Black carbon is considered as a signi cant contributor to climate change. It is emitted by both natural factors and human activities. It warms the air by absorbing solar energy and hence counts in one of the signi cant climate change pollutants. Black Carbon tends to hasten the melting of ice; hence when it falls on snow, it warms the snow and also its sooty nature darkens the surface of ice and snow. When Black Carbon enters the body, it causes cancer, cardiovascular disease, and birth defects.
China, along with India, comprises 25-35% of global Black Carbon emission. The usage of biofuels and coal is very high to satisfy the humankind demand in China, which results in the emission of a considerable amount of Black Carbon, which has fell in China by around 25% over the four weeks in January 2020 during the lockdown.

Conclusion
This study provides an analysis of changes in Air Quality  Figure 1 Pattern of COVID-19 con rmed cases as of 14th April 2020. Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors Figure 2 Study Area. Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors  Image showing the status of NO2 before and amid COVID-19 restrictions Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors Image showing the status of Black Carbon before and amid COVID-19 restrictions. Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors