Delhi’s pollution level has dipped. But that doesn’t mean policymakers can rest easy

Delhi’s air quality index shows that pollution levels have dipped with the onset of summer. That shouldn’t be a cause for complacency for policymakers. Analysis by the public-policy think tank Envirocatalysts underscores the need to continually monitor interactions between pollutants and meteorological conditions. Vehicular exhaust, construction dust, coal-based power generation, and waste-burning incidents do not change with the seasons. What changes, instead, is how these emissions behave once released into the atmosphere. In winter, temperature inversions and stagnant atmospheric conditions mean pollutants are trapped close to the ground, leading to high concentrations of particulate matter (PM). The Envirocatalysts study shows that in summer, emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) interact with the sun’s strong rays to produce ozone. The think tank’s analysis of Central Pollution Control Board data since 2015 shows that the concentration of the pollutant is the highest in May.

Ozone does not produce the haze associated with PM pollution. However, its public-health implications should not be downplayed. Short-term exposure can cause chest pain, cough and throat irritation, while in the long-term, it can exacerbate chronic respiratory diseases. Unlike PM, which affects both indoor and outdoor environments, ozone is primarily an outdoor pollutant but can infiltrate indoor spaces. It is also known to affect vegetation, damaging ecosystems.

The country’s air-quality standards and emergency response mechanisms — such as Delhi’s graded action plans — are largely built around PM thresholds. Regulatory frameworks often operate in silos, targeting specific pollutants without accounting for how they behave in different seasons. For example, measures to reduce vehicular emissions focus largely on particulate filters but overlook NOX emissions, which are critical precursors for ozone formation. VOC emissions are difficult to monitor because they originate from multiple sources. Fundamentally, however, the approach to reduce ozone pollution should not be very different from curbing PM emissions — it requires long-term shifts towards cleaner commuting modes, improving public transport, tighter fuel standards, and reduced dependence on coal-based energy generation. The Envirocatalysts study shows that poor air is becoming an all-weather problem in Delhi. It underlines the need for widening the lens through which pollution is understood.