New Delhi, May 7: A new public air quality dashboard has revealed a significant shift in Delhi pollution profile with ozone levels rising steadily even as traditional pollutants such as nitrogen dioxide (NO₂) and carbon monoxide (CO) show a gradual decline.
The dashboard built using long-term data from the Central Pollution Control Board (CPCB) and released by research organisation Envirocatalysts, provides a pollutant-wise analysis of trends in the national capital since 2015. Its findings point to a changing challenge: while efforts to curb emissions from vehicles and industries appear to be yielding results, a new and less visible threat is emerging in the form of ground-level ozone.
Data shows that Delhi’s annual average ozone concentration increased from 52 micrograms per cubic metre in 2021 to 66 micrograms per cubic metre in 2025. More strikingly, the number of days dominated by ozone pollution surged from 33 in 2024 to 76 in 2025, indicating a rapid escalation.
Unlike particulate pollution, which peaks during winter due to stagnant atmospheric conditions, ozone behaves differently. It rises during summer months, particularly in May, when intense sunlight triggers chemical reactions between nitrogen oxides and volatile organic compounds. This makes ozone a seasonal but increasingly serious concern.
At the same time, particulate matter continues to remain a major issue. PM2.5 levels, though showing a long-term decline from 117.5 micrograms per cubic metre in 2015 to 96.4 in 2025, still far exceed safe limits. PM10 levels have also reduced from 244 to 197 micrograms per cubic metre over the same period but remain persistently high, largely driven by dust from construction activities, roads, and open land.
Seasonal patterns remain evident. Pollution levels spike between October and February, when cooler temperatures and weak winds trap pollutants close to the ground. During the monsoon, air quality improves, not necessarily due to reduced emissions but because rainfall and stronger winds help disperse pollutants.
The data also highlights a broader regional trend across the National Capital Region (NCR). Cities such as Meerut, Noida, and Muzaffarnagar have recorded sharp increases in ozone levels, suggesting that the issue extends beyond Delhi. Meanwhile, areas like Ghaziabad and Gurugram continue to report high particulate pollution, reinforcing the interconnected nature of air quality across the region.
Recent monthly data underscores this divergence. While Delhi recorded an improvement in April 2026, with PM2.5 levels dropping to 68 micrograms per cubic metre from 77 a year earlier, neighbouring cities saw worsening conditions. Ghaziabad, Gurugram, and Faridabad all recorded higher PM2.5 levels than Delhi during the same period.
Experts say the findings signal a transition in the nature of urban air pollution. Measures targeting combustion-related emissions, such as cleaner fuels and stricter vehicle norms, may be reducing NO₂ and CO. However, these gains are being offset by rising ozone, which forms through complex atmospheric reactions and is harder to control directly.
The persistence of PM10 as a dominant pollutant accounting for over half of the polluted days in April further complicates the picture. It points to the growing influence of non-combustion sources such as dust, which require different policy interventions.
The emerging trend presents a new policy challenge. Tackling ozone pollution will require coordinated action on multiple fronts, including controlling precursor emissions, managing urban heat, and addressing regional transport of pollutants.
As Delhi air quality evolves data suggests that progress in one area does not necessarily translate into overall improvement. Instead, the city is entering a new phase where pollution is becoming more complex, requiring more nuanced and multi-layered solutions.