key: cord-1040607-shi0q9lz authors: Shukla, Saurabh; Khan, Ramsha; Saxena, Abhishek; Sekar, Selvam; Ali, Esmat F.; Shaheen, Sabry M. title: Appraisal of COVID-19 lockdown and unlocking effects on the air quality of North India date: 2021-09-22 journal: Environ Res DOI: 10.1016/j.envres.2021.112107 sha: 4b59a7315aaea5c53f064b143d06ee7f43813319 doc_id: 1040607 cord_uid: shi0q9lz The COVID-19 pandemic lockdown supposedly provided a ‘window’ of reinstatement to natural resources including the air quality, but the scenario after the phased unlocking is yet to be explored. Consequently, here we evaluated the status of air quality during the 8th phase of unlocking of COVID-19 lockdown (January 2021) at three locations of North India. The first site (S1) was located at Punjab Agricultural University, Ludhiana-PPCB; the second site (S2) at Yamunapuram, Bulandshahr-UPPCB; and the third site (S3) at Okhla Phase-2, Delhi-DPCC. The levels of PM2.5 showed a significant increase of 525.2%, 281.2%, and 185.0% at sites S1, S2 and S3, respectively in the unlock 8 (January 2021), in comparison to its concentration in the lockdown phase. Coherently, the levels of PM10 also showed a prominent increase of 284.5%, 189.1%, and 103.9% at sites S3, S1, and S2, respectively during the unlock 8 as compared to its concentration in the lockdown phase. This rise in the concentration of PM2.5 and PM10 could be primarily attributed to the use of biomass fuel, industrial and vehicular emissions, stubble burning considering the agricultural activities at sites S1 and S2. Site S3 is a major industrial hub and has the highest population density among all three sites. Consequently, the maximum increase (295.7%) in the NO(2) levels during the unlock 8 was witnessed at site S3. The strong correlation between PM2.5, PM10, and CO, along with the PM2.5/PM10 ratio confirmed the similar origin of these pollutants at all the three sites. The improvements in the levels of air quality during the COVID-19 lockdown were major overtaken during the various phases of unlocking consequent to the initiation of anthropogenic processes. The rapid pace of industrialization towards exhaustive development has impacted the quality (Shukla and Saxena, 2020) . These activities 83 have resulted into deterioration of air quality, which was also highlighted in a report 84 confirming that 12.5% out of the total deaths in India are caused due to air pollution (India The chemical composition of PM particles is highly diversified, potentially including metals 99 such as zinc, copper, nickel, iron, vanadium; organic compounds; biological compounds; 100 nitrates; and sulphates (WHO, 2013) . The 'small particles' include particles with diameter in 101 the range of 2.5 µm to 10 µm, and 'fine particles' with <2.5 µm diameter. Particulate matter 102 can enter into air through both natural and anthropogenic activities and is a significant sites S2 and S3, while the value of PM10 at S1 remained within the permissible limit (Fig. 4) . 248 The average concentration (µg/m 3 ) of PM10 during the lockdown phase at S1, S2, and S3 249 showed significant deterioration with concentrations of 44.6, 152.8, and 100.8, respectively. 250 It was noteworthy that the concentration of PM10 at site S2 and S3 remained above the 251 permissible limit, despite the lockdown. Site S2 is an agricultural district with widespread use 252 of biomass burning for household energy consumption. Hence, the probable impact of the 253 emissions from power plants, biomass burning for food preparation needs to be considered 254 due to their unstopped working even in the confinement period. Site S3 showed greater 255 reduction in the PM10 levels than site S1 and S2 signifying the impact of factory shutdown. Site S3 previously also topped the list of 50 most polluted cities as mentioned in a study by 257 Rodríguez-Urrego and Rodríguez-Urrego, (2020). The mean concentration of PM10 (µg/m 3 ) in the post-lockdown phase at S1 (119.0), S2 259 (268.0), and S3 (349.5) exceeded the permissible limit (Fig. 4) . The reopening of industrial The variation in the atmospheric concentration of NO2 on 24-hour basis in all three phases 266 (pre-lockdown, lockdown, and post-lockdown) has been illustrated in Table 2 and Fig. 5 . The 267 mean concentration of NO2 (µg/m 3 ) in the pre-lockdown phase was 26.5 at S1 48.5 at S2, and 268 48.2 at S3 (Table 2 ) and remained within the permissible limit (80 µg/m 3 ) (Fig. 5) . The 269 maximum value of NO2 at site S2 (88.1 µg/m 3 ) exceeded the permissible limit only on one 270 day (Fig. 5) . The positive impact of COVID-19 lockdown on air quality could be clearly seen on the low concentration of NO2 (µg/m 3 ) with mean concentrations remaining within the 272 permissible limits at S1 (19.9), S2 (16.1) and S3 (15.7) (Fig. 5) . 273 The average concentration of NO2 (µg/m 3 ) during the post-lockdown phase increased to 31.5 274 at S1, 15.7 at S2, and to 55.2 at S3; however, the mean concentration of NO2 at the three sites 275 were remained within the permissible limit (Fig. 5) . 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