{"title":"Meteorologically Normalized Air Quality Trends During COVID in India: Contrast Between Metro vs Non-metro Cities","authors":"Krishnakant Suryawanshi, Abhishek Chakraborty","doi":"10.1007/s41810-025-00315-2","DOIUrl":null,"url":null,"abstract":"<div><p>This study aimed to analyze the impact of a nationwide lockdown in India in response to the COVID-19 pandemic on air pollution by investigating variations in pollution levels while taking the meteorological factors into consideration. Air quality data collected from 12 monitoring stations, categorized as traffic, industrial, and other stations, were selected across metro and non-metro cities in India. To incorporate the impact of meteorological parameters into air quality parameters, a Random Forest (RF) machine learning (ML) model was utilized, assuming emissions remained at 2019 levels. Meteorological parameters and time variables were incorporated to predict business-as-usual (BAU) conditions. The findings revealed significant but varying reductions in fine particulate matter (PM<sub>2.5</sub>) and nitrogen dioxide (NO<sub>2</sub>) levels across all stations and city types during the lockdown. PM<sub>2.5</sub> levels decrement ranged from 13 to 54%, while NO<sub>2</sub> levels decrement ranged from 5 to 87%. Monitoring stations in Metro cities exhibited higher reductions than non-metro ones in NO<sub>2</sub> (average 55.7% compared to 28.3%) and PM<sub>2.5</sub> levels (average 38.8% compared to 30.2%). Ozone increased in metro cities likely due to reduced NO<sub>x</sub> levels in VOC-limited environments, whereas in non-metro cities, lower ozone formation may be linked to NO<sub>x</sub>-limited conditions were reductions in precursor emissions limited ozone production. The analysis also revealed that pollution levels during the lockdown period displayed relatively lower variations compared to normal conditions, suggesting fewer spikes/drops and faster recovery. Decreased correlations between NO<sub>2</sub> and CO in ten out of twelve stations suggested the emergence of new CO sources. An increase in the percentage of secondary components of PM<sub>2.5</sub> was observed, particularly in stations with O<sub>3</sub> increments, indicating that O<sub>3</sub> contributes to the formation of secondary PM<sub>2.5</sub>. This contrast emphasizes the severity of air pollution in Indian cities and underscores the urgency for comprehensive measures to address this issue.</p></div>","PeriodicalId":36991,"journal":{"name":"Aerosol Science and Engineering","volume":"10 4","pages":"568 - 581"},"PeriodicalIF":2.3000,"publicationDate":"2025-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Aerosol Science and Engineering","FirstCategoryId":"93","ListUrlMain":"https://link.springer.com/article/10.1007/s41810-025-00315-2","RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"ENVIRONMENTAL SCIENCES","Score":null,"Total":0}
引用次数: 0
Abstract
This study aimed to analyze the impact of a nationwide lockdown in India in response to the COVID-19 pandemic on air pollution by investigating variations in pollution levels while taking the meteorological factors into consideration. Air quality data collected from 12 monitoring stations, categorized as traffic, industrial, and other stations, were selected across metro and non-metro cities in India. To incorporate the impact of meteorological parameters into air quality parameters, a Random Forest (RF) machine learning (ML) model was utilized, assuming emissions remained at 2019 levels. Meteorological parameters and time variables were incorporated to predict business-as-usual (BAU) conditions. The findings revealed significant but varying reductions in fine particulate matter (PM2.5) and nitrogen dioxide (NO2) levels across all stations and city types during the lockdown. PM2.5 levels decrement ranged from 13 to 54%, while NO2 levels decrement ranged from 5 to 87%. Monitoring stations in Metro cities exhibited higher reductions than non-metro ones in NO2 (average 55.7% compared to 28.3%) and PM2.5 levels (average 38.8% compared to 30.2%). Ozone increased in metro cities likely due to reduced NOx levels in VOC-limited environments, whereas in non-metro cities, lower ozone formation may be linked to NOx-limited conditions were reductions in precursor emissions limited ozone production. The analysis also revealed that pollution levels during the lockdown period displayed relatively lower variations compared to normal conditions, suggesting fewer spikes/drops and faster recovery. Decreased correlations between NO2 and CO in ten out of twelve stations suggested the emergence of new CO sources. An increase in the percentage of secondary components of PM2.5 was observed, particularly in stations with O3 increments, indicating that O3 contributes to the formation of secondary PM2.5. This contrast emphasizes the severity of air pollution in Indian cities and underscores the urgency for comprehensive measures to address this issue.
期刊介绍：
ASE is an international journal that publishes high-quality papers, communications, and discussion that advance aerosol science and engineering. Acceptable article forms include original research papers, review articles, letters, commentaries, news and views, research highlights, editorials, correspondence, and new-direction columns. ASE emphasizes the application of aerosol technology to both environmental and technical issues, and it provides a platform not only for basic research but also for industrial interests. We encourage scientists and researchers to submit papers that will advance our knowledge of aerosols and highlight new approaches for aerosol studies and new technologies for pollution control. ASE promotes cutting-edge studies of aerosol science and state-of-art instrumentation, but it is not limited to academic topics and instead aims to bridge the gap between basic science and industrial applications. ASE accepts papers covering a broad range of aerosol-related topics, including aerosol physical and chemical properties, composition, formation, transport and deposition, numerical simulation of air pollution incidents, chemical processes in the atmosphere, aerosol control technologies and industrial applications. In addition, ASE welcomes papers involving new and advanced methods and technologies that focus on aerosol pollution, sampling and analysis, including the invention and development of instrumentation, nanoparticle formation, nano technology, indoor and outdoor air quality monitoring, air pollution control, and air pollution remediation and feasibility assessments.
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