Impacts on Air Quality Index in the Industrial town of Asansol (West Bengal, India) due to COVID-19 lockdown

The lockdown phase associated with COVID-19 pandemic initiated in full swing on and from 25th March, 2020 as preventive measures against the spreading of Corona virus. The objective of this study is to analyse the status of air quality of before and after lockdown in Asansol city which is second largest city of West Bengal, India and also known as “coal mining city”. Secondary data of ve parameters like CO, SO 2 , NO 2 , PM2.5 and PM10 have been collected from Central Pollution Control Board, India. The result shows signicant decrease of ve parameters from 42.4 % (CO) to 63.4 % (NO 2 ) due to close down of all industrial and transport activities during lockdown period. Based on different investigation a green belt development plan for this polluted city has been suggested for sustainable air quality management.

in an ongoing pandemic (Huang et al. 2020a, b;Zhou et al. 2020a, b;Zhu et al. 2020). The rst con rmed case has been traced back to 17 November 2019 and 20 January 2020 WHO issued a statement saying that there was evidence of human-to-human transmission. As of 17 August 2020, more than 26 lakhs cases have been reported across India, resulting in more than 52,000 deaths. Among the highly COVID-19 affected states in India, West Bengal stands at a vulnerable situation with 1,18,000 con rmed cases till August 15, 2020. Common symptoms include fever, cough, fatigue, shortness of breath, and loss of smell and taste. While most cases result in mild symptoms, some progress to acute respiratory distress syndrome (ARDS) possibly precipitated by cytokine storm, multi-organ failure, septic shock, and blood clots. The time from exposure to onset of symptoms is typically around ve days but may range from two to fourteen days.
The rst con rmed case of COVID-19 in India was reported on 30 January 2020 in the southern state of Kerala (Gautam and Hens 2020). Till now in India the most affected cities are Mumbai, Delhi, Chennai, Ahmedabad, Pune, Indore, Kolkata, Jaipur, Jodhpur etc. Finally, the CDC (Centres for Disease Control) declared that the virus can transmit person to person through respiratory droplets and thus an infected person can spread the virus to the healthy persons around them. This is spread through shaking of hands or any kinds of close personal contact (touching of eyes, nose, mouth). Infants, older people and those with medical problems like high blood pressure, cancer, diabetes, heart problem, asthma are more prone to develop this disease (Arabi et al. 2019;Ashour et al. 2020;Dong et al. 2020;).
Social lockdown is considered the most effective measure to control COVID-19 (Das and Patial 2020;Paital et al. 2020). On 19 th of March, honourable Prime Minister Narendra Modi rst declared for a lockdown of 21 days which was started through a 'JANATA CURFEW' on 22 nd March and from 25 th March 2020 lockdown started. There was a Lakhsman Rekha on our doorstep. All Indian cities were locked down and most industrial and commercial activities have been forced to stop their activities until further notice. Citizens are requested to stay at home and don't leave it except for very speci c reasons (buy essential supplies, medical appointments…). In add to these safety actions, the authorities decided also to shut down transportation and travel in and out of the country, close down schools, universities, restaurants and mosques, and to ban the mass gatherings across India. To prevent rapid transmission of coronavirus, countrywide lockdown had been enforced through the halting of economic production and restrictions on mobility of the citizens (Gautam and Hens 2020). Lockdown extended in India upto 31 st May 2020 and from 1 st June 2020 UNLOCK 1 started with lots of do's and don'ts.
Several studies reported that reducing anthropogenic activities during COVID-19 outbreak plays a signi cant role in air pollution formation and could in uence the total ambient air quality (He et al. 2020a;Isaifan 2020). PM10, NO 2 and SO 2 are very common ambient air pollutants in urban environments and caused severe health-related problems like respiratory and cardiovascular disorders, blood pressure and lung cancer (Koken et al., 2003;Le Tertre et al. 2002). These pollutants arise from anthropogenic sources, including road tra c and industrial activities (Thorpe and Harrison 2008;He et al. 2020b).
In this context, the objective of the present paper is to assess the atmospheric CO, SO 2 , NO 2 , PM2.5 and PM10 concentrations of industrial town, Asansol, before and after lockdown measures against the propagation of COVID-19 pandemic.

Materials And Methods a. Study site
In West Bengal, Asansol (23.673 0 N, 86.952 0 E) which is situated in the Western part of Burdwan district of West Bengal in the eastern India ( Fig. 1), is the second largest city of the state. It is also known as 'coal mining city' because, the entire region of Asansol sits on layers and layers of coal. The coal is of highquality superior coal.
Over the last ten years there was hectic development in the area in terms of industries like Indian Iron and Steel Company (IISCO), Burnpur Cement Limited (BCL), Dishergarh Power Supply Company limited, Joy Balaji Sponge Iron Private Limited, Shyam Gel Limited (Power Divisions) etc. In Asansol the ambient air quality has rapidly deteriorated (Banerjee et al. 2005(Banerjee et al. , 2006Dey 2013) due to mainly for industrialization, modernization, and urbanization, which is affecting human population, other animals, and plant communities.

b. Data sources and analysis
In this study, ve parameters like CO, SO 2 , NO 2 , PM2.5 and PM10 have been considered to evaluate the deviation of air quality before and after lockdown period (January 1, 2020 to July 31, 2020). The secondary data of above-mentioned selected pollution parameters has been obtained from the Central Pollution Control Board (CPCB), Govt. of India. The maps regarding variation of NO 2 and aerosol concentration over India have been obtained from European space agency (ESA) and the National aeronautics and Space Administration (NASA) individually (ESA 2020a; NASA 2020). The ve parameters (CO, SO 2 , NO 2 , PM2.5 and PM10) measured from January 1, 2020 to July 31, 2020 were subject to ANOVA using SYSTAT.

Results
Lockdown has transferred the air quality signi cantly which is re ected in the Table 1 and Fig. 2 (Table 2) also highlights signi cant variations in surface atmospheric CO, SO 2 , NO 2 , PM2.5 and PM10 between months.

Discussion
Rapid industrialization and urbanization lead to a great role in air pollution in Asansol City. For rapid spreading the contagious virus COVID-19, these factories, transports and other anthropogenic activities were completely shut down on and from 25 th March 2020, that resulted in the reduction of CO, SO 2 , NO 2 , PM2.5 and PM10 emission.
Air quality index (AQI) is the assessment of air quality and lower AQI means good air quality. The emission of CO, SO 2 , NO 2 , O 3 concentration are greatest environmental problem for developed countries (Sharma and Dhar 2018). NO 2 is emitted from high temperature combustion process of fossil fuels, ). According to report by European Space Agency (ESA) and National Aeronautics and Space Administration (NASA) suggests that environmental quality improved the emission of NO 2 reduced upto 30% (Source: ESA, 2020a and NASA Air Quality Analysis, 2020). NASA collects data using OMI (Ozone Monitoring Institute) on its AURA satellite. While ESA collects data through Sentinel -5P Satellite using TROPOMI (Tropospheric Monitoring Instrument and Ozone Monitoring Instrument). CO and SO 2 are an important indicators of air pollutants that are related to coal consumption, petroleum, and chemical fuel emissions. PM2.5 and PM10 derived from road tra c, industrial exhaust emission, construction works and road dust. Li et al., 2020, stated that at Yangtze river delta region in China, the emission of NO 2 , SO 2 and PM2.5 decreased in the air than the previous years. Similar result has been found in Almaty, Kazakastan by Kerimray et al. 2020 where CO, NO 2 and PM2.5 level reduced by 49%, 35% and 21% accordingly than prelockdown period. In European countries like France, Spain, Italy and Germany showed improved air quality during lockdown due to controlled vehicle movements, limited usage fuel energy and partially closed industrial sectors etc. (Muhammad et al. 2020;ESA 2020b). Even in Wuhan City, China 30% reduction of NO 2 was also found in 2020 than 2019 (He et al. 2020b). in Salé City, Morocco, the concentration of PM10, NO 2 and SO 2 were decreased respectively, by 75%, 96% and 49% within few days after implementation of COVID-19 lockdown (Otmani et al. 2020).

Like European countries and other Asian countries, India is also blessed with good air quality after 24 th
March 2020 (Mahato et al. 2020;Gautam 2020a;CPCB, 2020;Mate et al. 2020;Mitra et al. 2020;Lau et al. 2020). Sharma et al. 2020 also noticed remarkable positive modi cations of air quality (CO 2 , SO 2 , NO 2 , O 3 , PM2.5 and PM10) during March and April 2020 across the 22 cities in India than the same time period in 2017. Same result has been found by Bera et al. 2020 in Kolkata, West Bengal, where the pollutants like CO, SO 2 , NO 2 , PM2.5 and PM10 are signi cantly decreased during lockdown compared with previous three years because of complete stop of vehicle movement, burning of biomass and dust particles from construction works.
The long-term lockdown system diminishes the materialistic consumption and energy usage as per Jribi et al., 2020. Eroglu, 2020 noticed prominent decline in utilization of coal consumption during the rst half of 2020 in comparison with the past years. Presently, as the country is passing through lockdown phase, the industrial and transport activities are paused, reduces the concentration of CO, SO 2 , NO 2 , PM2.5 and PM10 in the atmosphere of industrial and most polluted city like Asansol, which is also a part of Raniganj Coal eld area.
From the environmental point of view lockdown is very much effective for air quality, but, in case of economic point of view of a country, it is not suggestable. So, for sustainable management of air quality, plants help us a lot, because they are the principal recipient of different types of air pollutants and act as a sink (Kaur and Nagpal, 2017)

Conclusion
This study investigates for better insight of COVID-19 and how current lockdown effects the various parameter like CO, SO 2 , NO 2 , PM2.5 and PM10 which is responsible for air pollution. The improvement of air quality opened our eye to the magnitude of damage caused by unregulated anthropogenic activities in the city. There is a chance that when the lockdown period is over environmental pollution can be back with more pace so human effort towards saving the environment can do everlasting effect. Strict implementation of environmental related laws along with mass awareness should be followed to ecorestore the city atmosphere. Tables   Table 1 Emission    The changing trend of atmospheric CO (mg/m3) during study period Figure 3 The changing trend of atmospheric SO2 (µg/m3), NO2 (µg/m3), PM2.5 (µg/m3) and PM10 (µg/m3) during study period