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Assessing air quality changes in large cities during COVID-19 lockdowns



Estimated average concentration of benzene in three days of spring in 2015–2019 (left) and 2020 (right), μg m−3.



Number of cities worlwide experienced air quality improvements during COVID-19 lockdowns; however,such changes may have been different in places with major contributions from nontraffic related sources.In Almaty, a city-scale quarantine came into force on March 19, 2020, which was a week after thefirstCOVID-19 case was registered in Kazakhstan. This study aims to analyze the effect of the lockdown fromMarch 19 to April 14, 2020 (27 days), on the concentrations of air pollutants in Almaty. Daily concentrationsof PM2.5,NO2,SO2,CO,O3, and BTEX were compared between the periods before and during the lockdown.During the lockdown, the PM2.5concentration was reduced by 21% with spatial variations of 6–34% com-pared to the average on the same days in 2018–2019, and still, it exceeded WHO daily limit values for18 days. There were also substantial reductions in CO and NO2concentrations by 49% and 35%, respectively,but an increase in O3levels by 15% compared to the prior 17 days before the lockdown. The concentrationsof benzene and toluene were 2–3 times higher than those during in the same seasons of 2015–2019. Thetemporal reductions may not be directly attributed to the lockdown due to favorable meteorological varia-tions during the period, but the spatial effects of the quarantine on the pollution levels are evidenced. Theresults demonstrate the impact of trafficonthecomplexnatureofairpollutioninAlmaty,whichissubstan-tially contributed by various nontraffic related sources, mainly coal-fired combined heat and power plants

and household heating systems, as well as possible small irregular sources such as garbage burning and bathhouses.


Conclusions


Every year, the air quality in Almaty improves gradually from Febru-ary to April due to seasonal changes in the temperature and precipita-tion, as well as due to a subsequent reduction of coal use at thecombined heat and power plants and in individual houses. Therefore,it was not reliable to perform a temporal analysis and attribute the tem-poral reductions to the traffic-free conditions. As an alternative methodto eliminate the weather impact, the same period was compared withthat during the previous years.There was a reduction in the PM2.5concentration by 21% in 2020(during lockdown) compared to the same period in 2018–2019 (beforelockdown), with substantial spatial variations. Although there was a30–34% reduction in PM2.5concentrations at the stations located atthe lower elevations, the air was still far from being clean at those loca-tions. Even under the low-traffic conditions in Almaty, the PM2.5con-centrations on 18 days of the lockdown period (out of total 27 days)exceeded the WHO daily limit values, providing evidence of the highcontribution from nontraffic related sources.The substantial reductions in CO and NO2concentrations during theCOVID-19 lockdown period compared to the 17 days before the lock-down could be due to the combination of traffic elimination and sea-sonal weather changes. Highly elevated concentrations of benzeneand toluene on three sampling days during the lockdown (101 and67μgm−3) and the toluene-to-benzene ratios suggest that these com-pounds originated from coal-related sources such as power plants andhouseholds and to possible episodic cases of garbage burning, bath-houses, and busfleet stations.This research demonstrates the complicated nature of air pollutionin Almaty, which urgently needs further investigation through spatialinventories and source-apportionment studies. The SARS-CoV-2 lock-down period was a unique opportunity to test how any possible reduc-tions in urban transport parameters may improve the air quality in thecity. The results suggest that even traffic-free conditions could not causesubstantial reductions in pollution levels since several primary emissionsources dominate the pollution profile over the city.Supplementary data to this article can be found online athttps://doi.org/10.1016/j.scitotenv.2020.139179


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https://reader.elsevier.com/reader/sd/pii/S0048969720326966?token=61F248578F94B02DA7051D63428621EAA718ADB2D90CDFEE9D7BF7B65680D468501AD1B20773E8E1CB155EE2A93747AA

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