Council on Energy, Environment and Water Integrated | International | Independent
Air pollution is often thought of as a winter problem or a North Indian issue. But many Indian cities like Delhi and Mumbai now experience elevated levels of air pollution in summer, too. Alongside ozone, Indian cities also see PM10 levels breaching the National Ambient Air Quality Standards (NAAQS) in this season. PM10 has generally been the dominant summer pollutant in Indian cities like Delhi, primarily due to dust. In contrast, the dominant winter pollutant is generally PM2.5, primarily from combustion sources.
Indian summers are harsh, with temperatures regularly crossing 40°C. Combined with air pollution, this extreme heat becomes a double burden for vulnerable populations like outdoor workers, school-going children, construction workers and the homeless.
Indian cities need action plans for summer air pollution, just as they do for winter. But before solutions, we need a clearer picture of the problem and its magnitude. This blog explains the key reasons behind summer air pollution and analyses PM10 and ozone data from six major cities–Delhi, Kolkata, Chennai, Bengaluru, Hyderabad and Mumbai–during April, May, and June in 2024 and 2025, to understand the severity of the issue and suggest possible interventions to combat it.
Road dust, construction dust, dust storms, and ozone formation due to vehicular pollution are the main sources behind summer air pollution in Indian cities.
Hot weather dries up soil, leaving loose particles to be easily picked up by the wind. This turns broken roads and barren land parcels into sources of particulate matter, leading to an increase in PM10 levels. In cities like Delhi, construction activity accelerates post-winter once the Commission for Air Quality Management in National Capital Region and Adjoining Areas (CAQM) lifts restrictions under the Graded Response Action Plan (GRAP). In other parts of the country, construction continues during and after winter until monsoons disrupt it.
Pre-monsoon dust storms are common in North India and contribute to increasing PM10 levels. Cities like Delhi and Jaipur receive pre-monsoon dust from western India and beyond, while Mumbai sometimes experiences storms carrying dust from the Arabian desert. PM10 exposure contributes to respiratory illnesses.
Vehicular emissions, alongside other pollutants like carbon monoxide and particulate matter, also contain nitrogen oxides (NOx) and Volatile Organic Compounds (VOCs) that react in the presence of sunlight to form ground-level ozone. This formation is higher in summer due to stronger sunlight and higher temperatures. While vehicles remain a major source of these compounds, industries, power plants and even domestic activities like painting also release these ozone precursors. Exposure to ozone can trigger asthma, bronchitis, and other lung ailments.
Safe PM10 levels breached across cities
Of the six cities, Delhi's PM10 levels exceeded the daily NAAQS limit of 100 μg/m3 by at least two times throughout summer.. While Mumbai and Kolkata's PM10 levels breached the daily NAAQS limit only on a few days, they were close to it on several days. PM10 levels stayed within the limit in Chennai, Bengaluru, and Hyderabad but occasionally hovered close to it.
In the case of ozone, at least one CAAQMS in Delhi exceeded the hourly NAAQS limit of 180 μg/m3 almost every day during summer. Delhi has a vehicle stock of over 80 lakh, with the second-largest private car ownership in the country after Bengaluru. Emissions from these vehicles, combined with Delhi’s harsh summers, make the city an ozone hotspot. While the ozone levels in the other five cities stayed within the limit on most days, a rise in temperature combined with an increase in emissions will increase the chances of ozone levels breaching the limit in the future.
Summer air pollution needs the same dedicated planning and attention as its winter counterpart. Although their sources may differ in nature and intensity, the solution remains consistent: stakeholders must come together to reduce emissions at the source.
Mohammad Rafiuddin is a Programme Lead, and Sneha Maria Ignatious is a Programme Associate at the Council on Energy, Environment and Water (CEEW). Send your comments to [email protected]
