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<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>

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Meteorologically Normalized Air Quality Trends During COVID in India: Contrast Between Metro vs Non-metro Cities

  • 期刊论文

  • 发表日期：

    2025年5月9日

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  • Krishnakant Suryawanshi,
  • Abhishek Chakraborty

摘要

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.