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COVID-19 and Air Pollution in Indian Cities: World’s Most Polluted Cities

COVID-19 and Air Pollution in Indian Cities: World’s Most Polluted Cities Special Issue on COVID-19 Aerosol Drivers, Impacts and Mitigation (VIII) Aerosol and Air Quality Research, 20: 2592–2603, 2020 ISSN: 1680-8584 print / 2071-1409 online Publisher: Taiwan Association for Aerosol Research https://doi.org/10.4209/aaqr.2020.05.0262 Sonal Kumari, Anita Lakhani, K. Maharaj Kumari Department of Chemistry, Faculty of Science, Dayalbagh Educational Institute, Dayalbagh, Agra 282110, India ABSTRACT th st In the present study, pollutants levels from 24 March-31 May in 2020 were compared with the same time period in 2019 to estimate the impact of lockdown on air pollutants levels in 39 different cities of India (including 10 Indian cities considered among the world’s 20 most polluted cities). Data for air pollutants was obtained from the Central Pollution Control Board (CPCB) which was statistically analyzed. Tropospheric NO2 column retrieved from Ozone Monitoring Instrument (OMI) were compared between 2019 and 2020 to compare the NO levels. Impact of lockdown measures on Ghaziabad which is the world’s most polluted city and Patiala which showed maximum reduction during the lockdown period in the present study was studied in detail. After the implementation of lockdown measures, air pollution decreased but with substantial variation among pollutants. The most significant reduction was observed for nitrogen dioxide (NO ) (3– 79%) and carbon monoxide (CO) (2–61%), pollutants which are mainly related to traffic emissions. Ozone (O ) showed a mixed trend with increasing levels at some cities which may be attributed to lower titration of O3 by NO. Maximum reduction observed in PM and PM was 58 and 57%, respectively during the lockdown period in 2020 as compared to the previous 10 2.5 year. Air quality of the cities also improved in 2020. During the lockdown period in 2020, AQI of only 15% of cities was in the ‘Unhealthy’ category (151–200) while in 2019, 56% of cities were in the ‘Unhealthy’ category. In Ghaziabad and Patiala all the pollutants showed significant reduction after lockdown implementation except O . Diurnal patterns of PM , PM , 3 10 2.5 CO and NO showed lower values during lockdown period in 2020 with less distinct bimodal patterns as compared to 2019. The present study provides evidence that widespread implementation of air pollution measures can result in immediate air quality benefits. Keywords: Lockdown; World’s most polluted cities; India; Air pollution reduction; AQI. modes of transport (trains, flights and cabs), public utilities INTRODUCTION and industrial activities were closed. Citizens were advised In late December 2019, novel infectious coronavirus to remain at home and to maintain social distancing. disease (COVID-19) was identified in Wuhan, China which On the basis of annual average of PM in 2019 IQAir 2.5 was later on confirmed to be transmitted human to human identified most polluted cities in the world with 13 Indian th through respiratory droplets (WHO, 2020). On 30 January, cities among the top 20 polluted cities (IQAir Report, 2019) the first confirmed case of COVID-19 in India was found. As (Table 1). Only 1% of the Indian population is exposed to rd of 23 March 2020, the number of COVID-19 cases increased less than the global WHO guideline level of annual mean –3 to 499 in India (https://www.worldometers.info/coronavirus/ PM (10 µg m ) (IEA, 2016). Major sources of PM in 2.5 2.5 country/india/) which was still very less than many other India are anthropogenic activities like fossil fuel combustion, countries like US, Italy and China. India being the world’s transportation, industrial emission (Venkataraman et al., second most populated country with many densely populated 2018). High levels of pollutants impose significant health cities had chances of spread of the virus at an accelerating issues (Chowdhury and Dey, 2016). In 2017, 1.24 million rate. To prevent the spread of the COVID-19, the government deaths in India (12.5% of the total deaths) were attributable th of India imposed nationwide lockdown from 24 March to to air pollution (Balakrishnan et al., 2019). Therefore, st 31 May. As a result, all non-essential services including efficient monitoring of air quality at the city level would schools, colleges, religious worship places, government offices, help in understanding the major contributing sources and the policy making for achieving better air quality. With the implementation of lockdown measures in India, a sudden break on all anthropogenic activities (mainly transportation Corresponding author. and industrial activities) improved the air quality. Delhi, the Tel.: 91-562-280154; Fax: 91-562-2801226 world’s most polluted capital city witnessed blue sky with E-mail address: maharajkumari.k@rediffmail.com about 49% reduction in air quality index (AQI) during the Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited. Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 2593 Table 1. PM annual average in 2019 reported by IQAir and AQI of cities and name and concentration of AQI species 2.5 th st –3 during 24 March–31 May 2019–2020 in 39 cities. 24-h average PM (µg m ), 8-h average O (ppb), 1-h average NO 2.5 3 2 (ppb) levels. PM AQI AQI 2.5 City (Rank AQI AQI Annual Specie and Specie th th according to Latitude Longitude (24 Mar (24 Mar– State Average its mean and its st st IQAir Report (°N) (°E) –31 May 31 May in 2019 level mean level 2019) 2019) 2020) –3 (µ g m ) (2019) (2020) Punjab Amritsar (147) 31.62 74.87 47.2 144 PM (53) 80 PM (26) 2.5 2.5 Ludhiana (127) 30.9 75.80 49.3 137 PM (50) 110 NO (146) 2.5 2 Patiala (310) 30.34 76.37 35.2 152 PM (57) 78 PM (25) 2.5 2.5 Rajasthan Udaipur 24.58 73.70 - 99 PM (35) 87 PM (29) 2.5 2.5 Bhiwadi (20) 28.20 76.83 83.4 178 PM (107) 147 PM (54) 2.5 2.5 Jaipur (120) 26.90 75.83 50.5 122 PM (44) 84 O (65) 2.5 3 Jodhpur (29) 26.29 73.03 77.2 177 PM (106) 151 PM (56) 2.5 2.5 Haryana Gurugram (7) 28.42 77.15 93.1 164 PM (80) 124 PM (45) 2.5 2.5 Jind (17) 29.32 76.30 85.4 158 PM (70) 126 O (78) 2.5 3 Faridabad (18) 28.41 77.32 85 190 O3 (101) 164 O3 (91) Rohtak (63) 28.87 76.62 59.7 166 PM (85) 127 PM (46) 2.5 2.5 Delhi Delhi (5) 28.61 76.98 98.6 166 O (92) 137 PM (51) 3 2.5 Assam Guwahati 26.18 91.78 - 127 PM (46) 127 PM (46) 2.5 2.5 Madhya Pradesh Bhopal (174) 23.22 77.19 44.6 168 PM (89) 115 O (75) 2.5 3 Ujjain (187) 23.18 75.77 43.4 151 O (86) 105 PM (37) 3 2.5 Uttar Pradesh Agra (80) 27.19 78.00 57.2 158 PM2.5 (69) 132 PM2.5 (48) Ghaziabad (1) 28.66 77.37 110.2 172 PM (97) 147 O (84) 2.5 3 Noida (6) 28.63 77.36 97.7 177 O (96) 129 PM (47) 3 2.5 Bulandshahr (13) 28.41 77.83 89.4 166 O (92) 161 O (90) 3 3 Kanpur (132) 26.47 80.32 48.5 156 PM (66) 129 PM (47) 2.5 2.5 Lucknow (11) 26.85 80.95 90.3 161 PM (75) 110 PM (39) 2.5 2.5 Greater Noida (9) 28.48 77.48 91.3 169 O3 (93) 136 O3 (81) Varanasi 25.32 82.97 - 192 O (102) 159 O (89) 3 3 Telangana Hyderabad (249) 17.46 78.33 39 99 PM (35) 74 PM (23) 2.5 2.5 Andra Pradesh Tirupati (560) 13.63 79.42 26.4 72 PM (22) 68 PM (20) 2.5 2.5 Visakhapatnam (180) 17.69 83.22 44 97 PM (34) 66 PM (19) 2.5 2.5 Gujarat Ahmedabad (69) 22.99 72.60 59 162 PM (76) 115 O (75) 2.5 3 Maharastra Mumbai (169) 19.06 72.83 45.3 68 PM (20) 114 NO (172) 2.5 2 Nagpur (146) 21.14 79.10 47.2 129 O (79) 100 NO (100) 3 2 Pune (299) 18.49 73.82 35.7 142 PM (52) 84 PM (28) 2.5 2.5 Tamil Nadu Chennai (320) 13.18 80.27 34.6 137 PM (50) 87 PM (29) 2.5 2.5 Kerela Thiruvananthapuram 8.51 76.95 27.9 80 PM (26) 66 PM (19) 2.5 2.5 (496) Jharkhand Jorapokhar 23.71 86.41 - 150 O (85) 147 O (84) 3 3 Bihar Gaya (65) 24.79 85.00 59.4 155 PM (64) 154 O (87) 2.5 3 Patna (22) 25.59 85.14 82.1 152 PM (57) 156 PM (66) 2.5 2.5 West Bengal Howrah (91) 22.57 88.30 55.9 122 PM (44) 72 PM (22) 2.5 2.5 Kolkata (61) 22.54 88.34 59.8 105 PM (37) 147 O (84) 2.5 3 Karnataka Bengaluru (361) 12.92 77.61 32.6 153 PM (60) 91 NO (92) 2.5 2 Kalaburagi 17.32 76.82 - 115 PM (41) 97 PM (34) 2.5 2.5 lockdown period (https://www.thehindu.com/news/cities/De SO pollutants in Malaysia however, Zhu et al. (2020) lhi/coronavirus-lockdown-lifts-delhis-march-air-quality-to- observed positive association between COVID-19 cases and 5-year-high/article31252221.ece). PM , PM , NO and O pollutants in China. Similar studies 10 2.5 2 3 Recent studies reported on short term exposure to air reported in China, Singapore, New York, Norway, Italy, pollution and COVID-19 infection have found significant United States, Spain, Turkey and Indonesia have analyzed positive association of air pollutants with COVID-19 the association between climate indicators (temperature, confirmed cases (Suhaimi et al., 2020; Zhu et al., 2020). rainfall, humidity, air quality) and COVID-19 and found a Suhaimi et al. (2020) found significant positive association significant association between them (Bashir et al., 2020; between COVID-19 cases and PM , PM , CO, NO and Gupta et al., 2020; Méndez-Arriaga, 2020; Menebo, 2020; 10 2.5 2 2594 Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 Pani et al., 2020; Sahin, 2020; Tobias et al., 2020; Tosepu showed statistical significant difference. et al., 2020; Xu et al., 2020; Yao et al., 2020). Temperature which is considered as an important parameter in development, Air Quality Index (AQI) prevention and control of an epidemic showed different Air Quality Index (AQI) is a numerical index used to correlation in different countries (Tobías and Molina, 2020). indicate the air quality of a region. AQI ranges in value from A significant positive correlation of COVID-19 cases with 0–500 with greater AQI value suggesting deteriorated air temperature is reported over Singapore, New York, Norway, quality and lower AQI (< 100) indicating satisfactory air quality Turkey and Indonesia highlighting the importance of in a region. In the present study, AQI values were derived from temperature in COVID-19 epidemic whereas a negative 24 h average PM and PM , 8 h average CO and O , 1 h 10 2.5 3 correlation is reported over Mexico while no correlation average NO and SO levels during lockdown period in 2019 2 2 between COVID-19 cases and temperature is observed in and 2020 using the U.S.EPA standard formula (U.S. EPA, China. 1999; Kumar and Goyal, 2011). The overall AQI considered Some studies have been reported in India assessing the for a city was the maximum AQI observed for that city. impact of COVID-19 lockdown on air quality but for limited number of cities and for short time period (Chauhan and Tropospheric NO Column Singh, 2020 (2 cities, Dec 2019–March 2020); Jain and Ozone Monitoring Instrument (OMI) daily tropospheric th th Sharma, 2020 (5 cities, 10 March–6 April 2019–2020); nitrogen dioxide column (OMNO2d version 3) at 0.25° × Kotnala et al., 2020 (1 city, January–March 2020); Kumar, 0.25° resolution is used in the study. OMI onboard Aura 2020 (6 cities, March–May 2020); Kumar et al., 2020 (5 satellite detects the backscattered solar radiation (wavelength cities, March–April 2015–2020); Mahato et al., 2020 (1 city, range of 270–500 nm) from the Earth and its atmosphere rd th 3 March–14 April 2020); Navinya et al., 2020 (17 cities, with a spatial resolution of 13 × 24 km (Krotkov et al., 2017). st rd 1 February–3 May 2019–2020); Sharma et al., 2020 (22 th th cities, 16 March–14 April 2017–2020); Shehzad et al., RESULTS AND DISCUSSION st th 2020 (2 cities, 1 January–20 April 2019–2020); Singh and Chauhan, 2020 (5 cities, March 2019–2020); Srivastava et AQI Values in Different Cities during the Lockdown st th th th al., 2020 (2 cities, 1 –20 February and 24 March–14 Period April 2020)). The present study was planned to describe the AQI values were determined for the lockdown period in th st changes in air pollutants levels during the complete lockdown 2019 and 2020 (24 March–31 May) (Fig. 1). In 2019, 56% th st period (24 March–31 May) in 39 different cities of India of cities were in the ‘Unhealthy’ category (151–200) and (including 10 Indian cities considered among the world’s only 16 and 28% cities lied in the ‘Moderate’ (51–100) and 20 most polluted cities) by using ground-based and satellite the ‘Unhealthy for sensitive group’ category (101–150) observations. (Table 1). In 2020, air quality of most of the cities improved with AQI of 36% of cities lying under the ‘Moderate’ METHODOLOGY category and 49% of cities in the ‘Unhealthy for sensitive group’ category. The largest drop in AQI values was observed Data Sources in Patiala (AQI improved by 74). A relatively higher number Data for particulate matter PM (particulate matter with of cities in Indo-Gangetic Plain showed lower AQI than diameter ≤ 10 µm), PM (particulate matter with diameter cities in other regions of India. Among the 10 most polluted 2.5 ≤ 2.5 µm), nitrogen dioxide (NO ), ozone (O ) sulfur dioxide Indian cities AQI in 7 cities reduced to 101–150 range from 2 3 (SO ) and carbon monoxide (CO) monitored by Central 151–200 range. This suggests that air quality has improved Pollution Control Board (CPCB) have been analyzed from significantly during the lockdown period in 2020. During th st 24 March–31 May in 2020 and compared with the same 2019 PM was the dominant pollutant in most of the cities 2.5 time period in 2019 for 39 cities of India. For Ghaziabad and (30 cities), however with reduction in AQI in 2020 the st rd Patiala a comparison of before (1 February–23 March) dominant species shifted to O and NO in some of the cities. 3 2 th st and during (24 March–31 May) lockdown period in 2019 For cities lying in the central region (Bhopal, Ahmedabad, and 2020 is done. Ten India cities (Ghaziabad (rank 1), Gaya, Kolkata, Jaipur, Ghaziabad and Jind) the dominant Delhi (5), Noida (6), Gurugram (7), Greater Noida (9), pollutant shifted to O however in some cities (Mumbai, Lucknow (11), Bulandshahr (13), Jind (17), Faridabad (18), Ludhiana, Bengaluru, Nagpur) it shifted to NO . In 2019 Bhiwadi (20)) considered in the world’s 20 most polluted dominance of PM in most of the cities suggests influence 2.5 cities and 29 other Indian cities were analyzed (IQAir on air quality by anthropogenic activities such as fossil fuel Report, 2019). Detailed information about these air quality combustion in road transport, industries and power generation. monitoring stations is given in Table 1. With reduction in PM levels during lockdown period in 2.5 Mean concentrations of the pollutants for the lockdown 2020 the emergence of O as the dominant pollutant suggests th st period (24 March–31 May) in 2019 and 2020 were calculated influence on air quality by secondary pollutants in some of to assess the variation between both periods having similar the cities. meteorology. Independent samples t-test between the mean concentration of all pollutants in 2019 and 2020 at 0.05 Variation in Pollutants Levels during the Lockdown significance level was carried out using Statistical Package Period in 2019 and 2020 for Social Sciences (SPSS) software. Most of the cities Further, average concentrations of pollutants in all 39 cities Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 2595 th st Fig. 1. AQI of 39 cities of India during lockdown period (24 March–31 May) in 2019 and 2020. were compared during the lockdown period in 2019 and vehicular emission and industrial activities (Sahu et al., 2012). 2020 to determine the impact of the lockdown measures on The number of registered vehicles in India in 2016 was air pollution levels (Fig. 2). Statistically significant differences around 230 million which has increased 4 times from 2001 in pollutants mean levels during the lockdown period in (http://mospi.nic.in/statistical-year-book-india/2018/189). 2019 and 2020 were observed at 0.05 significance level. This shows the dramatic increase in the vehicular population During the lockdown period in 2020, all cities showed in India. With the implementation of lockdown measures in drop in PM levels (except Guwahati and Jorapokhar) with India, all transportation facilities and industrial activities an overall reduction of 44% as compared to 2019. PM were stopped immediately. As these activities have a direct levels decreased by 8% (Kalaburagi) to 58% (Patiala) in 2020 effect on NO levels, an immediate reduction in NO is 2 2 as compared to 2019. Among the 10 most polluted cities of observed. During the lockdown period in 2020, NO reduced India, Gurugram showed maximum reduction in PM levels by 3% (Hyderabad) to 79% (Patiala) in India (overall mean (56%). Similar to PM , PM levels also reduced during the reduction 42%) (except at Agra, Jorapokhar, Ludhiana, Noida, 10 2.5 lockdown period in 2020. Average PM levels over all the Thiruvananthapuram and Patna). Similarly, reduction in NO 2.5 2 –3 –3 –3 cities decreased from 63.6 to 39.6 µg m (38% reduction). levels in Wuhan (22.8 µg m ) and China (12.9 µg m ) was PM levels showed reduction in all cities ranging from 1% also observed during the lockdown period (Zambrano- 2.5 (Guwahati) to 57 % (Patiala) except at Mumbai and Patna. Monserrate et al., 2020). To further substantiate the influence Top 10 most polluted cities showed reduction in the range of lockdown measures on NO levels, satellite-retrieved 33 to 51%. Higher reduction observed in PM levels than tropospheric NO column was also analyzed for the lockdown 10 2 PM can be due to the greater contribution of PM from period in 2019 and 2020 (Fig. 3) and a reduction in NO 2.5 10 2 anthropogenic activities (Klimont et al., 2017). In China, a levels during 2020 was found. Among 39 cities considered in reduction by 20–30% in PM levels during February 2020 the present study, maximum reduction by 54% in tropospheric 2.5 (lockdown period) in comparison to monthly averages of NO column over Patiala city (similar to ground observation) February in 2017–2019 based on satellite observation was was observed during the lockdown period in 2020 as found (CAMS, 2020). Cities situated in the northern region compared to 2019. NASA (National Aeronautics and Space (mainly in Uttar Pradesh) showed higher reduction in PM Administration) and ESA (European Space Agency) using and PM levels. Uttar Pradesh contributes the highest share satellite observations have also reported reduction in NO 2.5 2 in PM emission as compared to other states of India (Purohit emissions in Wuhan, Spain, Italy and USA by up to 30% 2.5 et al., 2019). The number of cities with daily 24 h mean PM during the lockdown period (Muhammad et al., 2020). and PM concentrations exceeding the National Ambient Air Tropospheric O is a secondary air pollutant which is 2.5 3 –3 Quality Standards (NAAQS: PM > 100 µ g m and PM photo-chemically formed from its precursors CO, nitrogen 10 2.5 –3 > 60 µ g m ) during the lockdown period in 2019 and 2020 oxides and volatile organic compounds (Kumari et al., 2018). were compared (NAAQS, 2009). 96% of cities in 2019 O levels at a site not only depend on precursor’s concentration exceeded the NAAQS limit for PM while in 2020, only but also on meteorological parameters. Sharma et al. (2020) 75% of cities violated the limit. Similarly, PM levels in found that meteorological parameters in India during the 2.5 2019 were exceeded by 80% of cities however, in 2020, only lockdown period in 2020 were similar to the analysis period 53% of cities exceeded the limit during the lockdown period. in the previous years. This suggests that O levels were NO is a primary pollutant which is emitted mainly from mainly influenced by precursor’s concentration during the 2596 Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 lockdown period in 2020. O levels in most of the cities central regions are VOC-sensitive (Sharma et al., 2016). The lying in the northern and central India were observed to be other reasons may be reduction in NO titration of O and increasing (1–27.7 ppb range) during the lockdown period reduced particulate matter levels as observed by similar study in 2020. This may be attributed by a decrease in NO levels during the lockdown period (Tobias et al., 2020). However, in VOCs sensitive environment as cities in the northern and other cities showed reduction in O levels during the lockdown th st Fig. 2. Mean concentrations of PM , PM , NO , O , CO and SO during 24 March–31 May in 2019 and 2020 (lockdown 10 2.5 2 3 2 period) (cities not showing statistical difference in mean values between 2019 and 2020 at 0.05 significance level are underlined). Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 2597 Fig. 3. Tropospheric NO column over India during lockdown period in 2019 and 2020. period (range 2 to 89 %). Among the 10 most polluted cities, SO levels in all cities was not observed. four cities showed higher levels in 2020 as compared to Similar to the present study reduction in PM , PM , 10 2.5 2019 with highest increase observed at Jind (47%). NO , CO and SO levels and a significant enhancement in 2 2 CO is one of the major air pollutants released from biomass O is observed at Iran, China, Kazakhstan, Singapore, burning and incomplete combustion of fossil fuels (Hollaway Morocco, Brazil, Malaysia and Spain (Table 2) (Broomandi et al., 2000). Similar to NO , CO levels also decreased (range et al., 2020; Chen et al., 2020; Kerimray et al., 2020; Li and 2–61%; overall mean reduction 28%) during the lockdown Tartarini, 2020; Otmani et al., 2020; Siciliano et al., 2020; period in 2020. However, in some of the cities (Delhi, Bhopal, Suhaimi et al., 2020; Tobias et al., 2020). Agra, Greater Noida, Patna, Tirupati, Pune, Kolkata, Noida and Jind) increase in CO levels during 2020 in comparison Ghaziabad: World’s Most Polluted City to 2019 was observed. Reduction in CO levels may be According to annual PM levels, Ghaziabad (annual 2.5 –3 attributed to the restrictions imposed on transportation facilities PM mean 110.2 µg m ) was found to be the world’s most 2.5 during the lockdown period in 2020. polluted city in 2019 (IQAir Report, 2019), therefore an in- SO also showed a mixed variation with reduction in most depth analysis of the impact of lockdown measures on of the cities (range 3–71%; overall mean reduction 40%) and pollutants levels was carried out there (Fig. 4). Ghaziabad is increase at some sites (Hyderabad, Kanpur, Varanasi, an industrial hub of India and comes in the part of National Jorapokhar, Thiruvananthapuram, Mumbai, Bengaluru, Ujjain, Capital Region (NCR) of Delhi. During lockdown period in Gaya, Lucknow, Agra, Bhopal and Jind). In India, 82% of 2020, average levels of PM (57%), PM (48%), CO (41%), 10 2.5 total SO emission originates from the industrial sector and SO (46%), O (6%) and NO (59%) showed reduction in 2 2 3 2 thermal power plants (Purohit et al., 2019), however during comparison to 2019 (Table 3). A significant difference in all the lockdown period in 2020 no restrictions were enforced pollutants levels during the lockdown period in 2019 and on thermal power plants. Therefore, a decreasing trend in 2020 at p < 0.05 was observed. 2598 Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 th st The time series plot of PM , PM , CO and NO was was observed. During II period (24 March–31 May), PM , 10 2.5 2 10 st rd similar in I period (1 February–23 March) in both years PM , CO and NO levels in 2020 were lower than 2019 2.5 2 while O showed higher values in 2020 as compared to 2019. however, O and SO showed some comparable values. 3 3 2 SO values in 2020 were comparatively lower than 2019 in Fig. 5 show the average diurnal patterns of PM , PM , 2 10 2.5 st rd I period. With the implementation of lockdown measures O , CO, NO and SO before (1 February–23 March) and 3 2 2 th th st from 24 March 2020, a sudden drop in all pollutants levels during lockdown period (24 March–31 May) in 2019 and Table 2. Percentage change in air pollutants levels in other countries during their lockdown period. – denotes reduction and + denotes increase in pollutant level. City, Country Study period Percentage change Reference st Tehran, Iran 21 March–21 April 2019– PM –11%; PM +10%; NO –13%; Broomandi et al. 10 2.5 2 2020 CO –13%; SO –12%; O +3% (2020) 2 3 China January–April 2017–2020 PM –15%; PM –14%; NO –16%; Chen et al. (2020) 10 2.5 2 (366 urban areas) CO –12%; SO –12%; O +9% 2 3 th th Almaty, Kazakhstan 19 March–14 April 2018– PM –21%; NO –35%; CO –49%; Kerimray et al. 2.5 2 2020 SO +7%; O +15% (2020) 2 3 th th Singapore 7 April–11 May 2016– PM –23%; PM –29%; NO –54%; Li and Tartarini, 10 2.5 2 (64 stations) 2020 CO –6%; SO –52%; O +18% (2020) 2 3 th nd Sale, Morocco 11 March–2 April 2020 PM –75%; NO –96%; SO –49% Otmani et al. 10 2 2 (2020) st th Iraja and Bangu, Brazil 1 March–16 April 2020 O +12.9, +6.3%, NO –46.1, –24.4% Siciliano et al. 3 x (2020) th st Kuala Lumpur (Klang 11 March–21 April 2018– PM –17 to –36%; NO –49 to –68%; Suhaimi et al. 2.5 2 Valley), Malaysia 2020 CO –21 to –48%; SO –6 to –26% (2020) th th Barcelona, Spain 16 February–30 March PM –28 to –31%; NO –47 to –51%; Tobias et al. 10 2 2020 SO –19 to +2%; O +28 to +58% (2020) 2 3 st st Fig. 4. Time series of hourly average PM , PM , CO, O , NO and SO levels during 1 February–31 May 2019 and 2020 10 2.5 3 2 2 in Ghaziabad (dotted line show starting of lockdown period). Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 2599 st rd Table 3. Mean concentrations of PM , PM , CO, O , NO and SO before (1 February–23 March) and during lockdown 10 2.5 3 2 2 th st period (24 March–31 May) in 2019 and 2020 in Ghaziabad. Pollutant 2019 I 2019 II 2020 I 2020 II st rd th st st rd th st (unit) (1 Feb–23 Mar 2019) (24 Mar–31 May 2019) (1 Feb–23 Mar 2020) (24 Mar–31 May 2020) –3 PM (µg m ) 205.4 ± 104.4 297.1 ± 135.1 210.9 ± 112.9 128.1 ± 76.3 –3 PM (µg m ) 117.7 ± 73.7 97.1 ± 61.1 113.9 ± 71.7 50.5 ± 37.2 2.5 CO (ppb) 1146.8 ± 785.2 1176.2 ± 932.4 1068.9 ± 739.9 695.4 ± 278.4 O (ppb) 9.8 ± 7.7 25.5 ± 20.8 17.9 ± 15.8 23.9 ± 19.8 NO (ppb) 37.9 ± 11.2 36.3 ± 16.2 31.6 ± 12.4 14.7 ± 6.4 SO (ppb) 8.2 ± 6.2 12.5 ± 10.7 5.2 ± 6 6.7 ± 8.7 st rd th Fig. 5. Average diurnal variation of PM , PM , CO, O , NO and SO during 1 February–23 March (I) and 24 March– 10 2.5 3 2 2 st 31 May (II) in 2019 and 2020 in Ghaziabad. st 2020 at Ghaziabad. The diurnal patterns of PM , PM , CO March–31 May), a very large variation in values of PM , 10 2.5 10 and NO2 were characterized by a bimodal pattern with PM2.5, CO and NO2 values was observed. PM10, PM2.5, CO –3 –3 morning and evening peaks. The morning peak of these and NO diurnal values were 225.8 µg m , 69.5 µg m , pollutants was observed at around 07:00–10:00 h and the 1094.6 ppb and 37.3 ppb, respectively lower in 2020 (during evening peak at around 22:00 h. These peaks correspond to the lockdown period) than 2019. Another significant peak traffic emission hours. The diurnal pattern of ozone difference in the diurnal pattern of PM , PM , CO and NO 10 2.5 2 was characterized by minimum value in early morning during II period was the reduction in the amplitude of the (07:00 h) and maximum value during afternoon (~14:00 h) pattern. The bimodal pattern of these pollutants was less due to photochemical formation. distinct in 2020 II period as compared to other periods. The On comparing the diurnal patterns of PM , PM , CO amplitudes of PM , PM , CO and NO were 61, 50, 68 and 10 2.5 10 2.5 2 st rd and NO during I period (1 February–23 March) in 2019 77%, respectively lower in II period in 2020 as compared to and 2020, similar patterns of PM10, PM2.5 and CO were 2019. This may be attributed to restrictions imposed on observed however, NO showed comparatively lower values transportation as vehicular emission is an important factor in 2020. Maximum difference observed in PM , PM , CO and responsible for the bimodal pattern of these pollutants. On 10 2.5 –3 –3 NO diurnal values was 49.1 µg m , 31.7 µg m , 446.4 ppb the other hand, secondary pollutant O showed higher variation 2 3 th and 17.4 ppb, respectively. During the II period (24 in 2020 during I period and similar pattern in both years 2600 Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 during II period. The diurnal pattern of O depends on the lockdown period in 2020, all pollutants showed statistical rate of photochemical generation, meteorological parameters: significant reduction. Average levels of PM (58%), temperature, solar radiation, relative humidity, wind speed, PM (57%), CO (61%), SO (13%) and NO (79%) showed 2.5 2 2 wind direction, planetary boundary layer height and rate of reduction in lockdown period in 2020 (II) however, O showed deposition (Kumari et al., 2020). Averaged diurnal variation an increase by 2% in comparison to 2019 (II) (Table 4). Mean of SO does not show a distinct pattern. Higher diurnal pollutants levels at Patiala were comparatively lower than values of SO in 2019 during both periods than 2020 were Ghaziabad during the study period however, comparatively observed. higher reduction during the lockdown period was observed at Patiala. Patiala: City with Maximum Reduction in Pollution Level Hourly average PM , PM , CO, O , NO and SO levels 10 2.5 3 2 2 st st In the present study, Patiala city showed maximum from 1 February–31 May in 2019 and 2020 were compared reduction in pollutants levels during the lockdown period in for Patiala city (Fig. 6). During I period, comparative levels 2020, therefore a detailed analysis of pollutants level was of PM , PM , O and SO were observed in both the years 2.5 10 3 2 also carried out at Patiala. Patiala is an agriculture-based city however, NO levels were low in 2020. With the situated in the northern Indo-Gangetic Plain. During the implementation of lockdown measures, pollutants showed st rd Table 4. Mean concentrations of PM , PM , CO, O , NO and SO before (1 February–23 March) and during lockdown 10 2.5 3 2 2 th st period (24 March–31 May) in 2019 and 2020 in Patiala. Pollutant 2019 I 2019 II 2020 I 2020 II st rd th st st rd th st (unit) (1 Feb–23 Mar 2019) (24 Mar–31 May 2019) (1 Feb–23 Mar 2020) (24 Mar–31 May 2020) –3 PM (µg m ) 111.3 ± 51.5 153 ± 84.3 81.8 ± 33.6 64 ± 41.7 –3 PM (µg m ) 40.1 ± 20.5 56.8 ± 24.3 37.2 ± 17.3 24.6 ± 15.2 2.5 CO (ppb) 557.8 ± 207.4 992 ± 518.8 679.6 ± 128.1 382.9 ± 57.9 O (ppb) 5.4 ± 3.9 10.1 ± 6.4 6.3 ± 4.6 10.3 ± 6.7 NO (ppb) 18.5 ± 11.3 22 ± 17.8 3.6 ± 1.5 4.6 ± 2.8 SO (ppb) 1.5 ± 0.8 3.1 ± 1.9 2.7 ± 1.8 2.7 ± 2.2 st st Fig. 6. Time series of hourly average PM , PM , CO, O , NO and SO levels during 1 February–31 May 2019 and 2020 10 2.5 3 2 2 in Patiala (dotted line show starting of lockdown period). Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 2601 st rd th Fig. 7. Average diurnal variation of PM , PM , CO, O , NO and SO during 1 February–23 March (I) and 24 March– 10 2.5 3 2 2 st 31 May (II) in 2019 and 2020 in Patiala. th sudden reduction in levels (on 24 March 2020). PM , result air pollution levels dropped significantly. The present 2.5 PM , CO, NO and SO levels were lower in 2020 II period study provides detail of the impact of lockdown on air 10 2 2 as compared to 2019 II period whereas O levels were pollution in 39 different cities of India. The primary pollutant comparable. A similar variation was observed at Ghaziabad. concentrations (PM , PM , CO and NO ) showed decreased 10 2.5 2 Similar to Ghaziabad, bimodal diurnal patterns of PM , levels in all cities however, secondary pollutant (O ) showed 10 3 PM , CO and NO were observed in Patiala (Fig. 7). O both increasing and decreasing trends. Overall 44, 38, 28, 42 2.5 2 3 showed a unimodal diurnal pattern however, no distinct diurnal and 40% reduction was observed in PM , PM , CO, NO 10 2.5 2 pattern of SO was observed. During I period, diurnal patterns and SO levels, respectively during the lockdown period in 2 2 of PM , PM , O and CO were comparable. Maximum 2020 as compared to 2019. Reduced primary pollutants were 10 2.5 3 deviation observed in PM , PM , CO, O , NO and SO mainly attributed to restrictions imposed on transportation 10 2.5 3 2 2 –3 –3 diurnal values was 53.1 µg m , 8.2 µg m , 239.6 ppb, and industrial activities as these activities are their primary 2.5 ppb, 17.8 ppb and 2.8 ppb, respectively. During II period, sources. Increase in O levels may be due to reduced NO diurnal patterns were comparatively lower in 2020 except titration. Though the reduction observed in the pollutants levels for O . Maximum reduction observed in the diurnal values during the lockdown period is expected to be short-lived, it –3 of PM , PM , CO, O , NO and SO was 118.8 µg m , provides evidence that widespread implementation of air 10 2.5 3 2 2 –3 31.4 µg m , 869.1 ppb, 3.1 ppb, 21.9 ppb and 2.1 ppb, pollution measures can result in immediate air quality benefits. respectively. The amplitude of the pattern was also lower as Therefore, in worst air quality scenario restrictions on compared to 2019 II period and no clear bimodal patterns of vehicles and industries can help in improving the air quality. PM , PM , CO and NO were observed. Amplitudes of 10 2.5 2 PM , PM , CO and NO were 75, 61, 78 and 94% lower, 10 2.5 2 ACKNOWLEDGEMENT respectively in 2020 II period. This may be attributed by restrictions imposed on vehicular activities. The authors are thankful to the Director, Dayalbagh Educational Institute, Agra, and the Head, Department of CONCLUSION Chemistry, for the necessary help. 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COVID-19 and Air Pollution in Indian Cities: World’s Most Polluted Cities

Aerosol and Air Quality ResearchJan 1, 2020

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Abstract

Special Issue on COVID-19 Aerosol Drivers, Impacts and Mitigation (VIII) Aerosol and Air Quality Research, 20: 2592–2603, 2020 ISSN: 1680-8584 print / 2071-1409 online Publisher: Taiwan Association for Aerosol Research https://doi.org/10.4209/aaqr.2020.05.0262 Sonal Kumari, Anita Lakhani, K. Maharaj Kumari Department of Chemistry, Faculty of Science, Dayalbagh Educational Institute, Dayalbagh, Agra 282110, India ABSTRACT th st In the present study, pollutants levels from 24 March-31 May in 2020 were compared with the same time period in 2019 to estimate the impact of lockdown on air pollutants levels in 39 different cities of India (including 10 Indian cities considered among the world’s 20 most polluted cities). Data for air pollutants was obtained from the Central Pollution Control Board (CPCB) which was statistically analyzed. Tropospheric NO2 column retrieved from Ozone Monitoring Instrument (OMI) were compared between 2019 and 2020 to compare the NO levels. Impact of lockdown measures on Ghaziabad which is the world’s most polluted city and Patiala which showed maximum reduction during the lockdown period in the present study was studied in detail. After the implementation of lockdown measures, air pollution decreased but with substantial variation among pollutants. The most significant reduction was observed for nitrogen dioxide (NO ) (3– 79%) and carbon monoxide (CO) (2–61%), pollutants which are mainly related to traffic emissions. Ozone (O ) showed a mixed trend with increasing levels at some cities which may be attributed to lower titration of O3 by NO. Maximum reduction observed in PM and PM was 58 and 57%, respectively during the lockdown period in 2020 as compared to the previous 10 2.5 year. Air quality of the cities also improved in 2020. During the lockdown period in 2020, AQI of only 15% of cities was in the ‘Unhealthy’ category (151–200) while in 2019, 56% of cities were in the ‘Unhealthy’ category. In Ghaziabad and Patiala all the pollutants showed significant reduction after lockdown implementation except O . Diurnal patterns of PM , PM , 3 10 2.5 CO and NO showed lower values during lockdown period in 2020 with less distinct bimodal patterns as compared to 2019. The present study provides evidence that widespread implementation of air pollution measures can result in immediate air quality benefits. Keywords: Lockdown; World’s most polluted cities; India; Air pollution reduction; AQI. modes of transport (trains, flights and cabs), public utilities INTRODUCTION and industrial activities were closed. Citizens were advised In late December 2019, novel infectious coronavirus to remain at home and to maintain social distancing. disease (COVID-19) was identified in Wuhan, China which On the basis of annual average of PM in 2019 IQAir 2.5 was later on confirmed to be transmitted human to human identified most polluted cities in the world with 13 Indian th through respiratory droplets (WHO, 2020). On 30 January, cities among the top 20 polluted cities (IQAir Report, 2019) the first confirmed case of COVID-19 in India was found. As (Table 1). Only 1% of the Indian population is exposed to rd of 23 March 2020, the number of COVID-19 cases increased less than the global WHO guideline level of annual mean –3 to 499 in India (https://www.worldometers.info/coronavirus/ PM (10 µg m ) (IEA, 2016). Major sources of PM in 2.5 2.5 country/india/) which was still very less than many other India are anthropogenic activities like fossil fuel combustion, countries like US, Italy and China. India being the world’s transportation, industrial emission (Venkataraman et al., second most populated country with many densely populated 2018). High levels of pollutants impose significant health cities had chances of spread of the virus at an accelerating issues (Chowdhury and Dey, 2016). In 2017, 1.24 million rate. To prevent the spread of the COVID-19, the government deaths in India (12.5% of the total deaths) were attributable th of India imposed nationwide lockdown from 24 March to to air pollution (Balakrishnan et al., 2019). Therefore, st 31 May. As a result, all non-essential services including efficient monitoring of air quality at the city level would schools, colleges, religious worship places, government offices, help in understanding the major contributing sources and the policy making for achieving better air quality. With the implementation of lockdown measures in India, a sudden break on all anthropogenic activities (mainly transportation Corresponding author. and industrial activities) improved the air quality. Delhi, the Tel.: 91-562-280154; Fax: 91-562-2801226 world’s most polluted capital city witnessed blue sky with E-mail address: maharajkumari.k@rediffmail.com about 49% reduction in air quality index (AQI) during the Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited. Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 2593 Table 1. PM annual average in 2019 reported by IQAir and AQI of cities and name and concentration of AQI species 2.5 th st –3 during 24 March–31 May 2019–2020 in 39 cities. 24-h average PM (µg m ), 8-h average O (ppb), 1-h average NO 2.5 3 2 (ppb) levels. PM AQI AQI 2.5 City (Rank AQI AQI Annual Specie and Specie th th according to Latitude Longitude (24 Mar (24 Mar– State Average its mean and its st st IQAir Report (°N) (°E) –31 May 31 May in 2019 level mean level 2019) 2019) 2020) –3 (µ g m ) (2019) (2020) Punjab Amritsar (147) 31.62 74.87 47.2 144 PM (53) 80 PM (26) 2.5 2.5 Ludhiana (127) 30.9 75.80 49.3 137 PM (50) 110 NO (146) 2.5 2 Patiala (310) 30.34 76.37 35.2 152 PM (57) 78 PM (25) 2.5 2.5 Rajasthan Udaipur 24.58 73.70 - 99 PM (35) 87 PM (29) 2.5 2.5 Bhiwadi (20) 28.20 76.83 83.4 178 PM (107) 147 PM (54) 2.5 2.5 Jaipur (120) 26.90 75.83 50.5 122 PM (44) 84 O (65) 2.5 3 Jodhpur (29) 26.29 73.03 77.2 177 PM (106) 151 PM (56) 2.5 2.5 Haryana Gurugram (7) 28.42 77.15 93.1 164 PM (80) 124 PM (45) 2.5 2.5 Jind (17) 29.32 76.30 85.4 158 PM (70) 126 O (78) 2.5 3 Faridabad (18) 28.41 77.32 85 190 O3 (101) 164 O3 (91) Rohtak (63) 28.87 76.62 59.7 166 PM (85) 127 PM (46) 2.5 2.5 Delhi Delhi (5) 28.61 76.98 98.6 166 O (92) 137 PM (51) 3 2.5 Assam Guwahati 26.18 91.78 - 127 PM (46) 127 PM (46) 2.5 2.5 Madhya Pradesh Bhopal (174) 23.22 77.19 44.6 168 PM (89) 115 O (75) 2.5 3 Ujjain (187) 23.18 75.77 43.4 151 O (86) 105 PM (37) 3 2.5 Uttar Pradesh Agra (80) 27.19 78.00 57.2 158 PM2.5 (69) 132 PM2.5 (48) Ghaziabad (1) 28.66 77.37 110.2 172 PM (97) 147 O (84) 2.5 3 Noida (6) 28.63 77.36 97.7 177 O (96) 129 PM (47) 3 2.5 Bulandshahr (13) 28.41 77.83 89.4 166 O (92) 161 O (90) 3 3 Kanpur (132) 26.47 80.32 48.5 156 PM (66) 129 PM (47) 2.5 2.5 Lucknow (11) 26.85 80.95 90.3 161 PM (75) 110 PM (39) 2.5 2.5 Greater Noida (9) 28.48 77.48 91.3 169 O3 (93) 136 O3 (81) Varanasi 25.32 82.97 - 192 O (102) 159 O (89) 3 3 Telangana Hyderabad (249) 17.46 78.33 39 99 PM (35) 74 PM (23) 2.5 2.5 Andra Pradesh Tirupati (560) 13.63 79.42 26.4 72 PM (22) 68 PM (20) 2.5 2.5 Visakhapatnam (180) 17.69 83.22 44 97 PM (34) 66 PM (19) 2.5 2.5 Gujarat Ahmedabad (69) 22.99 72.60 59 162 PM (76) 115 O (75) 2.5 3 Maharastra Mumbai (169) 19.06 72.83 45.3 68 PM (20) 114 NO (172) 2.5 2 Nagpur (146) 21.14 79.10 47.2 129 O (79) 100 NO (100) 3 2 Pune (299) 18.49 73.82 35.7 142 PM (52) 84 PM (28) 2.5 2.5 Tamil Nadu Chennai (320) 13.18 80.27 34.6 137 PM (50) 87 PM (29) 2.5 2.5 Kerela Thiruvananthapuram 8.51 76.95 27.9 80 PM (26) 66 PM (19) 2.5 2.5 (496) Jharkhand Jorapokhar 23.71 86.41 - 150 O (85) 147 O (84) 3 3 Bihar Gaya (65) 24.79 85.00 59.4 155 PM (64) 154 O (87) 2.5 3 Patna (22) 25.59 85.14 82.1 152 PM (57) 156 PM (66) 2.5 2.5 West Bengal Howrah (91) 22.57 88.30 55.9 122 PM (44) 72 PM (22) 2.5 2.5 Kolkata (61) 22.54 88.34 59.8 105 PM (37) 147 O (84) 2.5 3 Karnataka Bengaluru (361) 12.92 77.61 32.6 153 PM (60) 91 NO (92) 2.5 2 Kalaburagi 17.32 76.82 - 115 PM (41) 97 PM (34) 2.5 2.5 lockdown period (https://www.thehindu.com/news/cities/De SO pollutants in Malaysia however, Zhu et al. (2020) lhi/coronavirus-lockdown-lifts-delhis-march-air-quality-to- observed positive association between COVID-19 cases and 5-year-high/article31252221.ece). PM , PM , NO and O pollutants in China. Similar studies 10 2.5 2 3 Recent studies reported on short term exposure to air reported in China, Singapore, New York, Norway, Italy, pollution and COVID-19 infection have found significant United States, Spain, Turkey and Indonesia have analyzed positive association of air pollutants with COVID-19 the association between climate indicators (temperature, confirmed cases (Suhaimi et al., 2020; Zhu et al., 2020). rainfall, humidity, air quality) and COVID-19 and found a Suhaimi et al. (2020) found significant positive association significant association between them (Bashir et al., 2020; between COVID-19 cases and PM , PM , CO, NO and Gupta et al., 2020; Méndez-Arriaga, 2020; Menebo, 2020; 10 2.5 2 2594 Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 Pani et al., 2020; Sahin, 2020; Tobias et al., 2020; Tosepu showed statistical significant difference. et al., 2020; Xu et al., 2020; Yao et al., 2020). Temperature which is considered as an important parameter in development, Air Quality Index (AQI) prevention and control of an epidemic showed different Air Quality Index (AQI) is a numerical index used to correlation in different countries (Tobías and Molina, 2020). indicate the air quality of a region. AQI ranges in value from A significant positive correlation of COVID-19 cases with 0–500 with greater AQI value suggesting deteriorated air temperature is reported over Singapore, New York, Norway, quality and lower AQI (< 100) indicating satisfactory air quality Turkey and Indonesia highlighting the importance of in a region. In the present study, AQI values were derived from temperature in COVID-19 epidemic whereas a negative 24 h average PM and PM , 8 h average CO and O , 1 h 10 2.5 3 correlation is reported over Mexico while no correlation average NO and SO levels during lockdown period in 2019 2 2 between COVID-19 cases and temperature is observed in and 2020 using the U.S.EPA standard formula (U.S. EPA, China. 1999; Kumar and Goyal, 2011). The overall AQI considered Some studies have been reported in India assessing the for a city was the maximum AQI observed for that city. impact of COVID-19 lockdown on air quality but for limited number of cities and for short time period (Chauhan and Tropospheric NO Column Singh, 2020 (2 cities, Dec 2019–March 2020); Jain and Ozone Monitoring Instrument (OMI) daily tropospheric th th Sharma, 2020 (5 cities, 10 March–6 April 2019–2020); nitrogen dioxide column (OMNO2d version 3) at 0.25° × Kotnala et al., 2020 (1 city, January–March 2020); Kumar, 0.25° resolution is used in the study. OMI onboard Aura 2020 (6 cities, March–May 2020); Kumar et al., 2020 (5 satellite detects the backscattered solar radiation (wavelength cities, March–April 2015–2020); Mahato et al., 2020 (1 city, range of 270–500 nm) from the Earth and its atmosphere rd th 3 March–14 April 2020); Navinya et al., 2020 (17 cities, with a spatial resolution of 13 × 24 km (Krotkov et al., 2017). st rd 1 February–3 May 2019–2020); Sharma et al., 2020 (22 th th cities, 16 March–14 April 2017–2020); Shehzad et al., RESULTS AND DISCUSSION st th 2020 (2 cities, 1 January–20 April 2019–2020); Singh and Chauhan, 2020 (5 cities, March 2019–2020); Srivastava et AQI Values in Different Cities during the Lockdown st th th th al., 2020 (2 cities, 1 –20 February and 24 March–14 Period April 2020)). The present study was planned to describe the AQI values were determined for the lockdown period in th st changes in air pollutants levels during the complete lockdown 2019 and 2020 (24 March–31 May) (Fig. 1). In 2019, 56% th st period (24 March–31 May) in 39 different cities of India of cities were in the ‘Unhealthy’ category (151–200) and (including 10 Indian cities considered among the world’s only 16 and 28% cities lied in the ‘Moderate’ (51–100) and 20 most polluted cities) by using ground-based and satellite the ‘Unhealthy for sensitive group’ category (101–150) observations. (Table 1). In 2020, air quality of most of the cities improved with AQI of 36% of cities lying under the ‘Moderate’ METHODOLOGY category and 49% of cities in the ‘Unhealthy for sensitive group’ category. The largest drop in AQI values was observed Data Sources in Patiala (AQI improved by 74). A relatively higher number Data for particulate matter PM (particulate matter with of cities in Indo-Gangetic Plain showed lower AQI than diameter ≤ 10 µm), PM (particulate matter with diameter cities in other regions of India. Among the 10 most polluted 2.5 ≤ 2.5 µm), nitrogen dioxide (NO ), ozone (O ) sulfur dioxide Indian cities AQI in 7 cities reduced to 101–150 range from 2 3 (SO ) and carbon monoxide (CO) monitored by Central 151–200 range. This suggests that air quality has improved Pollution Control Board (CPCB) have been analyzed from significantly during the lockdown period in 2020. During th st 24 March–31 May in 2020 and compared with the same 2019 PM was the dominant pollutant in most of the cities 2.5 time period in 2019 for 39 cities of India. For Ghaziabad and (30 cities), however with reduction in AQI in 2020 the st rd Patiala a comparison of before (1 February–23 March) dominant species shifted to O and NO in some of the cities. 3 2 th st and during (24 March–31 May) lockdown period in 2019 For cities lying in the central region (Bhopal, Ahmedabad, and 2020 is done. Ten India cities (Ghaziabad (rank 1), Gaya, Kolkata, Jaipur, Ghaziabad and Jind) the dominant Delhi (5), Noida (6), Gurugram (7), Greater Noida (9), pollutant shifted to O however in some cities (Mumbai, Lucknow (11), Bulandshahr (13), Jind (17), Faridabad (18), Ludhiana, Bengaluru, Nagpur) it shifted to NO . In 2019 Bhiwadi (20)) considered in the world’s 20 most polluted dominance of PM in most of the cities suggests influence 2.5 cities and 29 other Indian cities were analyzed (IQAir on air quality by anthropogenic activities such as fossil fuel Report, 2019). Detailed information about these air quality combustion in road transport, industries and power generation. monitoring stations is given in Table 1. With reduction in PM levels during lockdown period in 2.5 Mean concentrations of the pollutants for the lockdown 2020 the emergence of O as the dominant pollutant suggests th st period (24 March–31 May) in 2019 and 2020 were calculated influence on air quality by secondary pollutants in some of to assess the variation between both periods having similar the cities. meteorology. Independent samples t-test between the mean concentration of all pollutants in 2019 and 2020 at 0.05 Variation in Pollutants Levels during the Lockdown significance level was carried out using Statistical Package Period in 2019 and 2020 for Social Sciences (SPSS) software. Most of the cities Further, average concentrations of pollutants in all 39 cities Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 2595 th st Fig. 1. AQI of 39 cities of India during lockdown period (24 March–31 May) in 2019 and 2020. were compared during the lockdown period in 2019 and vehicular emission and industrial activities (Sahu et al., 2012). 2020 to determine the impact of the lockdown measures on The number of registered vehicles in India in 2016 was air pollution levels (Fig. 2). Statistically significant differences around 230 million which has increased 4 times from 2001 in pollutants mean levels during the lockdown period in (http://mospi.nic.in/statistical-year-book-india/2018/189). 2019 and 2020 were observed at 0.05 significance level. This shows the dramatic increase in the vehicular population During the lockdown period in 2020, all cities showed in India. With the implementation of lockdown measures in drop in PM levels (except Guwahati and Jorapokhar) with India, all transportation facilities and industrial activities an overall reduction of 44% as compared to 2019. PM were stopped immediately. As these activities have a direct levels decreased by 8% (Kalaburagi) to 58% (Patiala) in 2020 effect on NO levels, an immediate reduction in NO is 2 2 as compared to 2019. Among the 10 most polluted cities of observed. During the lockdown period in 2020, NO reduced India, Gurugram showed maximum reduction in PM levels by 3% (Hyderabad) to 79% (Patiala) in India (overall mean (56%). Similar to PM , PM levels also reduced during the reduction 42%) (except at Agra, Jorapokhar, Ludhiana, Noida, 10 2.5 lockdown period in 2020. Average PM levels over all the Thiruvananthapuram and Patna). Similarly, reduction in NO 2.5 2 –3 –3 –3 cities decreased from 63.6 to 39.6 µg m (38% reduction). levels in Wuhan (22.8 µg m ) and China (12.9 µg m ) was PM levels showed reduction in all cities ranging from 1% also observed during the lockdown period (Zambrano- 2.5 (Guwahati) to 57 % (Patiala) except at Mumbai and Patna. Monserrate et al., 2020). To further substantiate the influence Top 10 most polluted cities showed reduction in the range of lockdown measures on NO levels, satellite-retrieved 33 to 51%. Higher reduction observed in PM levels than tropospheric NO column was also analyzed for the lockdown 10 2 PM can be due to the greater contribution of PM from period in 2019 and 2020 (Fig. 3) and a reduction in NO 2.5 10 2 anthropogenic activities (Klimont et al., 2017). In China, a levels during 2020 was found. Among 39 cities considered in reduction by 20–30% in PM levels during February 2020 the present study, maximum reduction by 54% in tropospheric 2.5 (lockdown period) in comparison to monthly averages of NO column over Patiala city (similar to ground observation) February in 2017–2019 based on satellite observation was was observed during the lockdown period in 2020 as found (CAMS, 2020). Cities situated in the northern region compared to 2019. NASA (National Aeronautics and Space (mainly in Uttar Pradesh) showed higher reduction in PM Administration) and ESA (European Space Agency) using and PM levels. Uttar Pradesh contributes the highest share satellite observations have also reported reduction in NO 2.5 2 in PM emission as compared to other states of India (Purohit emissions in Wuhan, Spain, Italy and USA by up to 30% 2.5 et al., 2019). The number of cities with daily 24 h mean PM during the lockdown period (Muhammad et al., 2020). and PM concentrations exceeding the National Ambient Air Tropospheric O is a secondary air pollutant which is 2.5 3 –3 Quality Standards (NAAQS: PM > 100 µ g m and PM photo-chemically formed from its precursors CO, nitrogen 10 2.5 –3 > 60 µ g m ) during the lockdown period in 2019 and 2020 oxides and volatile organic compounds (Kumari et al., 2018). were compared (NAAQS, 2009). 96% of cities in 2019 O levels at a site not only depend on precursor’s concentration exceeded the NAAQS limit for PM while in 2020, only but also on meteorological parameters. Sharma et al. (2020) 75% of cities violated the limit. Similarly, PM levels in found that meteorological parameters in India during the 2.5 2019 were exceeded by 80% of cities however, in 2020, only lockdown period in 2020 were similar to the analysis period 53% of cities exceeded the limit during the lockdown period. in the previous years. This suggests that O levels were NO is a primary pollutant which is emitted mainly from mainly influenced by precursor’s concentration during the 2596 Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 lockdown period in 2020. O levels in most of the cities central regions are VOC-sensitive (Sharma et al., 2016). The lying in the northern and central India were observed to be other reasons may be reduction in NO titration of O and increasing (1–27.7 ppb range) during the lockdown period reduced particulate matter levels as observed by similar study in 2020. This may be attributed by a decrease in NO levels during the lockdown period (Tobias et al., 2020). However, in VOCs sensitive environment as cities in the northern and other cities showed reduction in O levels during the lockdown th st Fig. 2. Mean concentrations of PM , PM , NO , O , CO and SO during 24 March–31 May in 2019 and 2020 (lockdown 10 2.5 2 3 2 period) (cities not showing statistical difference in mean values between 2019 and 2020 at 0.05 significance level are underlined). Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 2597 Fig. 3. Tropospheric NO column over India during lockdown period in 2019 and 2020. period (range 2 to 89 %). Among the 10 most polluted cities, SO levels in all cities was not observed. four cities showed higher levels in 2020 as compared to Similar to the present study reduction in PM , PM , 10 2.5 2019 with highest increase observed at Jind (47%). NO , CO and SO levels and a significant enhancement in 2 2 CO is one of the major air pollutants released from biomass O is observed at Iran, China, Kazakhstan, Singapore, burning and incomplete combustion of fossil fuels (Hollaway Morocco, Brazil, Malaysia and Spain (Table 2) (Broomandi et al., 2000). Similar to NO , CO levels also decreased (range et al., 2020; Chen et al., 2020; Kerimray et al., 2020; Li and 2–61%; overall mean reduction 28%) during the lockdown Tartarini, 2020; Otmani et al., 2020; Siciliano et al., 2020; period in 2020. However, in some of the cities (Delhi, Bhopal, Suhaimi et al., 2020; Tobias et al., 2020). Agra, Greater Noida, Patna, Tirupati, Pune, Kolkata, Noida and Jind) increase in CO levels during 2020 in comparison Ghaziabad: World’s Most Polluted City to 2019 was observed. Reduction in CO levels may be According to annual PM levels, Ghaziabad (annual 2.5 –3 attributed to the restrictions imposed on transportation facilities PM mean 110.2 µg m ) was found to be the world’s most 2.5 during the lockdown period in 2020. polluted city in 2019 (IQAir Report, 2019), therefore an in- SO also showed a mixed variation with reduction in most depth analysis of the impact of lockdown measures on of the cities (range 3–71%; overall mean reduction 40%) and pollutants levels was carried out there (Fig. 4). Ghaziabad is increase at some sites (Hyderabad, Kanpur, Varanasi, an industrial hub of India and comes in the part of National Jorapokhar, Thiruvananthapuram, Mumbai, Bengaluru, Ujjain, Capital Region (NCR) of Delhi. During lockdown period in Gaya, Lucknow, Agra, Bhopal and Jind). In India, 82% of 2020, average levels of PM (57%), PM (48%), CO (41%), 10 2.5 total SO emission originates from the industrial sector and SO (46%), O (6%) and NO (59%) showed reduction in 2 2 3 2 thermal power plants (Purohit et al., 2019), however during comparison to 2019 (Table 3). A significant difference in all the lockdown period in 2020 no restrictions were enforced pollutants levels during the lockdown period in 2019 and on thermal power plants. Therefore, a decreasing trend in 2020 at p < 0.05 was observed. 2598 Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 th st The time series plot of PM , PM , CO and NO was was observed. During II period (24 March–31 May), PM , 10 2.5 2 10 st rd similar in I period (1 February–23 March) in both years PM , CO and NO levels in 2020 were lower than 2019 2.5 2 while O showed higher values in 2020 as compared to 2019. however, O and SO showed some comparable values. 3 3 2 SO values in 2020 were comparatively lower than 2019 in Fig. 5 show the average diurnal patterns of PM , PM , 2 10 2.5 st rd I period. With the implementation of lockdown measures O , CO, NO and SO before (1 February–23 March) and 3 2 2 th th st from 24 March 2020, a sudden drop in all pollutants levels during lockdown period (24 March–31 May) in 2019 and Table 2. Percentage change in air pollutants levels in other countries during their lockdown period. – denotes reduction and + denotes increase in pollutant level. City, Country Study period Percentage change Reference st Tehran, Iran 21 March–21 April 2019– PM –11%; PM +10%; NO –13%; Broomandi et al. 10 2.5 2 2020 CO –13%; SO –12%; O +3% (2020) 2 3 China January–April 2017–2020 PM –15%; PM –14%; NO –16%; Chen et al. (2020) 10 2.5 2 (366 urban areas) CO –12%; SO –12%; O +9% 2 3 th th Almaty, Kazakhstan 19 March–14 April 2018– PM –21%; NO –35%; CO –49%; Kerimray et al. 2.5 2 2020 SO +7%; O +15% (2020) 2 3 th th Singapore 7 April–11 May 2016– PM –23%; PM –29%; NO –54%; Li and Tartarini, 10 2.5 2 (64 stations) 2020 CO –6%; SO –52%; O +18% (2020) 2 3 th nd Sale, Morocco 11 March–2 April 2020 PM –75%; NO –96%; SO –49% Otmani et al. 10 2 2 (2020) st th Iraja and Bangu, Brazil 1 March–16 April 2020 O +12.9, +6.3%, NO –46.1, –24.4% Siciliano et al. 3 x (2020) th st Kuala Lumpur (Klang 11 March–21 April 2018– PM –17 to –36%; NO –49 to –68%; Suhaimi et al. 2.5 2 Valley), Malaysia 2020 CO –21 to –48%; SO –6 to –26% (2020) th th Barcelona, Spain 16 February–30 March PM –28 to –31%; NO –47 to –51%; Tobias et al. 10 2 2020 SO –19 to +2%; O +28 to +58% (2020) 2 3 st st Fig. 4. Time series of hourly average PM , PM , CO, O , NO and SO levels during 1 February–31 May 2019 and 2020 10 2.5 3 2 2 in Ghaziabad (dotted line show starting of lockdown period). Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 2599 st rd Table 3. Mean concentrations of PM , PM , CO, O , NO and SO before (1 February–23 March) and during lockdown 10 2.5 3 2 2 th st period (24 March–31 May) in 2019 and 2020 in Ghaziabad. Pollutant 2019 I 2019 II 2020 I 2020 II st rd th st st rd th st (unit) (1 Feb–23 Mar 2019) (24 Mar–31 May 2019) (1 Feb–23 Mar 2020) (24 Mar–31 May 2020) –3 PM (µg m ) 205.4 ± 104.4 297.1 ± 135.1 210.9 ± 112.9 128.1 ± 76.3 –3 PM (µg m ) 117.7 ± 73.7 97.1 ± 61.1 113.9 ± 71.7 50.5 ± 37.2 2.5 CO (ppb) 1146.8 ± 785.2 1176.2 ± 932.4 1068.9 ± 739.9 695.4 ± 278.4 O (ppb) 9.8 ± 7.7 25.5 ± 20.8 17.9 ± 15.8 23.9 ± 19.8 NO (ppb) 37.9 ± 11.2 36.3 ± 16.2 31.6 ± 12.4 14.7 ± 6.4 SO (ppb) 8.2 ± 6.2 12.5 ± 10.7 5.2 ± 6 6.7 ± 8.7 st rd th Fig. 5. Average diurnal variation of PM , PM , CO, O , NO and SO during 1 February–23 March (I) and 24 March– 10 2.5 3 2 2 st 31 May (II) in 2019 and 2020 in Ghaziabad. st 2020 at Ghaziabad. The diurnal patterns of PM , PM , CO March–31 May), a very large variation in values of PM , 10 2.5 10 and NO2 were characterized by a bimodal pattern with PM2.5, CO and NO2 values was observed. PM10, PM2.5, CO –3 –3 morning and evening peaks. The morning peak of these and NO diurnal values were 225.8 µg m , 69.5 µg m , pollutants was observed at around 07:00–10:00 h and the 1094.6 ppb and 37.3 ppb, respectively lower in 2020 (during evening peak at around 22:00 h. These peaks correspond to the lockdown period) than 2019. Another significant peak traffic emission hours. The diurnal pattern of ozone difference in the diurnal pattern of PM , PM , CO and NO 10 2.5 2 was characterized by minimum value in early morning during II period was the reduction in the amplitude of the (07:00 h) and maximum value during afternoon (~14:00 h) pattern. The bimodal pattern of these pollutants was less due to photochemical formation. distinct in 2020 II period as compared to other periods. The On comparing the diurnal patterns of PM , PM , CO amplitudes of PM , PM , CO and NO were 61, 50, 68 and 10 2.5 10 2.5 2 st rd and NO during I period (1 February–23 March) in 2019 77%, respectively lower in II period in 2020 as compared to and 2020, similar patterns of PM10, PM2.5 and CO were 2019. This may be attributed to restrictions imposed on observed however, NO showed comparatively lower values transportation as vehicular emission is an important factor in 2020. Maximum difference observed in PM , PM , CO and responsible for the bimodal pattern of these pollutants. On 10 2.5 –3 –3 NO diurnal values was 49.1 µg m , 31.7 µg m , 446.4 ppb the other hand, secondary pollutant O showed higher variation 2 3 th and 17.4 ppb, respectively. During the II period (24 in 2020 during I period and similar pattern in both years 2600 Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 during II period. The diurnal pattern of O depends on the lockdown period in 2020, all pollutants showed statistical rate of photochemical generation, meteorological parameters: significant reduction. Average levels of PM (58%), temperature, solar radiation, relative humidity, wind speed, PM (57%), CO (61%), SO (13%) and NO (79%) showed 2.5 2 2 wind direction, planetary boundary layer height and rate of reduction in lockdown period in 2020 (II) however, O showed deposition (Kumari et al., 2020). Averaged diurnal variation an increase by 2% in comparison to 2019 (II) (Table 4). Mean of SO does not show a distinct pattern. Higher diurnal pollutants levels at Patiala were comparatively lower than values of SO in 2019 during both periods than 2020 were Ghaziabad during the study period however, comparatively observed. higher reduction during the lockdown period was observed at Patiala. Patiala: City with Maximum Reduction in Pollution Level Hourly average PM , PM , CO, O , NO and SO levels 10 2.5 3 2 2 st st In the present study, Patiala city showed maximum from 1 February–31 May in 2019 and 2020 were compared reduction in pollutants levels during the lockdown period in for Patiala city (Fig. 6). During I period, comparative levels 2020, therefore a detailed analysis of pollutants level was of PM , PM , O and SO were observed in both the years 2.5 10 3 2 also carried out at Patiala. Patiala is an agriculture-based city however, NO levels were low in 2020. With the situated in the northern Indo-Gangetic Plain. During the implementation of lockdown measures, pollutants showed st rd Table 4. Mean concentrations of PM , PM , CO, O , NO and SO before (1 February–23 March) and during lockdown 10 2.5 3 2 2 th st period (24 March–31 May) in 2019 and 2020 in Patiala. Pollutant 2019 I 2019 II 2020 I 2020 II st rd th st st rd th st (unit) (1 Feb–23 Mar 2019) (24 Mar–31 May 2019) (1 Feb–23 Mar 2020) (24 Mar–31 May 2020) –3 PM (µg m ) 111.3 ± 51.5 153 ± 84.3 81.8 ± 33.6 64 ± 41.7 –3 PM (µg m ) 40.1 ± 20.5 56.8 ± 24.3 37.2 ± 17.3 24.6 ± 15.2 2.5 CO (ppb) 557.8 ± 207.4 992 ± 518.8 679.6 ± 128.1 382.9 ± 57.9 O (ppb) 5.4 ± 3.9 10.1 ± 6.4 6.3 ± 4.6 10.3 ± 6.7 NO (ppb) 18.5 ± 11.3 22 ± 17.8 3.6 ± 1.5 4.6 ± 2.8 SO (ppb) 1.5 ± 0.8 3.1 ± 1.9 2.7 ± 1.8 2.7 ± 2.2 st st Fig. 6. Time series of hourly average PM , PM , CO, O , NO and SO levels during 1 February–31 May 2019 and 2020 10 2.5 3 2 2 in Patiala (dotted line show starting of lockdown period). Kumari et al., Aerosol and Air Quality Research, 20: 2592–2603, 2020 2601 st rd th Fig. 7. Average diurnal variation of PM , PM , CO, O , NO and SO during 1 February–23 March (I) and 24 March– 10 2.5 3 2 2 st 31 May (II) in 2019 and 2020 in Patiala. th sudden reduction in levels (on 24 March 2020). PM , result air pollution levels dropped significantly. The present 2.5 PM , CO, NO and SO levels were lower in 2020 II period study provides detail of the impact of lockdown on air 10 2 2 as compared to 2019 II period whereas O levels were pollution in 39 different cities of India. The primary pollutant comparable. A similar variation was observed at Ghaziabad. concentrations (PM , PM , CO and NO ) showed decreased 10 2.5 2 Similar to Ghaziabad, bimodal diurnal patterns of PM , levels in all cities however, secondary pollutant (O ) showed 10 3 PM , CO and NO were observed in Patiala (Fig. 7). O both increasing and decreasing trends. Overall 44, 38, 28, 42 2.5 2 3 showed a unimodal diurnal pattern however, no distinct diurnal and 40% reduction was observed in PM , PM , CO, NO 10 2.5 2 pattern of SO was observed. During I period, diurnal patterns and SO levels, respectively during the lockdown period in 2 2 of PM , PM , O and CO were comparable. Maximum 2020 as compared to 2019. Reduced primary pollutants were 10 2.5 3 deviation observed in PM , PM , CO, O , NO and SO mainly attributed to restrictions imposed on transportation 10 2.5 3 2 2 –3 –3 diurnal values was 53.1 µg m , 8.2 µg m , 239.6 ppb, and industrial activities as these activities are their primary 2.5 ppb, 17.8 ppb and 2.8 ppb, respectively. During II period, sources. Increase in O levels may be due to reduced NO diurnal patterns were comparatively lower in 2020 except titration. Though the reduction observed in the pollutants levels for O . Maximum reduction observed in the diurnal values during the lockdown period is expected to be short-lived, it –3 of PM , PM , CO, O , NO and SO was 118.8 µg m , provides evidence that widespread implementation of air 10 2.5 3 2 2 –3 31.4 µg m , 869.1 ppb, 3.1 ppb, 21.9 ppb and 2.1 ppb, pollution measures can result in immediate air quality benefits. respectively. The amplitude of the pattern was also lower as Therefore, in worst air quality scenario restrictions on compared to 2019 II period and no clear bimodal patterns of vehicles and industries can help in improving the air quality. PM , PM , CO and NO were observed. Amplitudes of 10 2.5 2 PM , PM , CO and NO were 75, 61, 78 and 94% lower, 10 2.5 2 ACKNOWLEDGEMENT respectively in 2020 II period. This may be attributed by restrictions imposed on vehicular activities. The authors are thankful to the Director, Dayalbagh Educational Institute, Agra, and the Head, Department of CONCLUSION Chemistry, for the necessary help. 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