The story so far:In March, the Commission for Air Quality Management in the National Capital Region and Adjoining Areas (CAQM) revoked all curbs under the Graded Response Action Plan (GRAP), signalling the end of the winter air pollution in Delhi.A month later, as temperatures rose, it reimposed Stage 1 of the GRAP to combat summer air pollution. It was briefly revoked and reimposed again in May, while North India was reeling under heatwaves.Why are cities witnessing pollution episodes during summer?Delhi and the Indo-Gangetic plain are known for winter smog because low temperatures, low wind speeds, and their basin-like topography trap pollutants close to the ground.Summer brings stronger winds, occasional thunderstorms that wash out pollutants, and warmer temperatures that allow pollutants to mix higher in the atmosphere. Despite such meteorological favours, Delhi has already witnessed 54 days between 1 April and 31 May 2026 where daily average PM10 levels exceeded the 24-hour National Ambient Air Quality Standard (NAAQS) of 100 ug/m3. At the same time, on 40 days, at least one Continuous Ambient Air Quality Monitoring Station (CAAQMS) in the city recorded a breach in the hourly ozone standard of 180 ug/m3.Unlike most headlines, this is not the story of Delhi alone. Other large cities like Mumbai, Chennai, Hyderabad, Bengaluru, and Kolkata also recorded pollution spikes in the same period this summer, with PM10 and ozone levels going above the national standards to varying degrees. These spikes were shaped by local sources such as vehicular emissions, road dust, construction activity, industrial emissions, and dust from local storms. Mumbai, for instance, has been recording high PM10 and ozone levels over the last few years due to construction activity, dust, and traffic. While Chennai’s PM10 breaches are occasional, its high vehicular density and hot weather also make it an ozone hotspot.How is summer air pollution different from that in winter?While winter pollution is dominated by finer PM2.5 particles, summer air pollution is driven by the coarser PM10 and ozone.Vehicles, industries, waste burning, agricultural residue burning, construction sites, and broken roads remain year-round sources of pollution. Winter adds biomass burning for heating. Summer brings in dust storms that hike PM10 levels, while heat and sunlight catalyse ozone formation.Why does ozone rise in hot weather?Ozone is not emitted directly from a tailpipe or chimney. It forms when nitrogen oxides (NOx), largely from vehicles and volatile organic compounds (VOCs) from industrial emissions, vehicle exhaust, paints, and other sources, react under strong sunlight. Hotter, sunnier days therefore create favourable conditions for ozone formation, which, along with particulate matter, could cause respiratory illnesses.What causes India’s PM10 to spike?Hot conditions over the Indian subcontinent create a low-pressure area that extends towards Iran. Its interaction with surrounding high-pressure areas produces hot, windy conditions. These winds could stir up dust storms, including hot winds called loo, which carry dust from West Asia and the Thar Desert across India towards the Bay of Bengal. Such episodes could elevate PM10 levels for days, as seen during the severe North Indian dust storms of 2018.The Indian subcontinent also experiences shorter, localised dust storms known as ‘andhi’ that usually subside within hours. These form when strong downward-moving air associated with thunderstorms hits the ground, lifts loose dust, and carries it at high speed. While loo-type dust storms are common in North India, cities like Mumbai and Hyderabad generally face dusty episodes due to local thunderstorms.Human activity worsens this natural dust load. Construction and demolition work often resumes after the more stringent winter GRAP restrictions are lifted. Without adequate site-level dust control, these activities add to PM10 levels. Vehicles moving over broken roads also further resuspend loose, dry dust into the air in the dry summer months.What can cities do to combat summer air pollution?While natural sources of dust cannot be controlled, they can be predicted. Delhi’s Air Quality Early Warning System (AQEWS) was created in response to severe dust storms in 2018 and smog episodes of the previous years, and now runs year-round. It has since been extended to other cities such as Jaipur and Mumbai, and provides forecasts of multiple pollutants several days in advance. Its bulletin provides detailed weather information for Delhi and three-day Air Quality Index forecasts for 140 Indian cities.The India Meteorological Department (IMD) also publishes national weather forecast bulletins several times a day. Authorities should use these systems to issue local alerts on dust storms, ozone, and poor air quality so citizens can reduce exposure.For controllable non-natural sources, enforcement matters. Construction sites need active dust management even outside winter.A study by the Council on Energy, Environment and Water (CEEW) found that simply reducing heavy-vehicle movement at construction sites can lower local particulate matter levels. The Brihanmumbai Municipal Corporation (BMC)’s Air Quality Decision Support System (AQDSS), also developed with CEEW, for example, assists in monitoring construction sites. It has already helped authorities take measures against more than 1,000 sites since October 2025 in Mumbai.Reducing ozone requires cutting NOx and VOC emissions from vehicles and industries through cleaner transport, better compliance, and attention to solvents, paints, and fuel combustion. Even simple behavioural measures, like the ‘Red Light On, Gaadi Off’ campaign of the Delhi government that urges drivers to switch vehicles off while waiting at junctions to reduce idling emissions, can reduce ozone formation. But Indian cities need more sustained action.Delhi has had a summer action plan since 2022. Other cities need similar plans that combine forecasting, public health advisories, construction dust control, road dust management, and action on ozone-forming emissions. Summer may disperse some pollutants better than winter, but heat and sunlight create their own pollution chemistry. Indian cities must plan for both seasons, treating them with equal seriousness.(Mohammad Rafiuddin is Programme Lead and Sneha Maria Ignatious is Programme Associate at the Council on Energy, Environment and Water)