Impact of Particulate Matter-Centric Clean Air Action Plans on Ozone Concentrations in India

Abstract

The grim status of India’s air quality is commonly attributed to alarming levels of particulate matter (PM). This has led to the government formulating several strategies to control PM in the country. For example, the National Clean Air Programme (NCAP) was launched in 2019 to reduce 30% PM concentrations by 2024 in nonattainment cities (NACs). However, studies across the world found these PM-centric action plans to be detrimental to ozone-related air quality. The present study is among the first few investigations that employ the Weather Research and Forecasting coupled with Chemistry (WRF-Chem) model to comprehensively understand the effect of the NCAP on PM and ozone in India. In the 2024 business-as-usual scenario, while 50% of NACs have deteriorating PM2.5 levels, all but 32% of other NACs meet the Indian National Ambient Air Quality Standards (INAAQS) with the NCAP. The NACs that violated the INNAQS are mainly situated in the Indo-Gangetic Plain. For ozone, with the implementation of the NCAP, 80% of NACs meet the INAAQS. This reduction in ozone is attributed to the indicator ratio of formaldehyde to oxides of nitrogen (HCHO/NOy), indicating that the Indian region is volatile organic compound-limited (VOC-limited), and thereby, reduction in nitrogen oxides and VOC emissions results in a decrease in ozone. Further, another reason can be the increase in forest cover as a part of the NCAP, which has increased ozone deposition velocity by ∼10.5%. This study indicates that the current action plans of India, if implemented successfully, can also alleviate the problem of secondary pollutants like ozone, saving around 12% of lives.

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“…The escalating urbanization and industrialization, coupled with associated human activities, have precipitated a surge in pollutant emissions and a significant deterioration in air quality throughout India. The government has intermittently introduced a variety of regulatory measures to combat the pervasive issue of air pollution such as the Graded Response Action Plan (GRAP), which categorizes and enforces measures by relevant authorities during periods of poor air quality. − One recent governmental strategy is the National Clean Air Programme (NCAP), with the goal of reducing particulate matter (PM) levels by approximately 40% within a seven-year timeframe in the 131 non-attainment cities of India. − …”