Pollution shift: Delhi’s air quality dashboard shows rise in Ozone as NO2, CO decline

However, this seasonal dip does not necessarily indicate lower emissions. Instead, meteorological conditions such as rainfall and stronger winds help disperse pollutants more effectively, temporarily improving air quality index (AQI).

In contrast, the data shows that ozone peaks during summer, particularly in May, when strong sunlight drives photochemical reactions between nitrogen oxides and volatile organic compounds.

Delhi’s annual average ozone rose from 52 µg/m³ (micrograms per cubic metre) in 2021 to 66 µg/m³ in 2025, alongside a sharp increase in ozone-dominant days, from 33 µg/m³ in 2024 to 76 µg/m³ in 2025.

Among cities with consistent data across five years, the steepest increases were recorded in Meerut (53 µg/m³ to 76 µg/m³), Noida (54 µg/m³ to 74 µg/m³ ), and Muzaffarnagar (55 µg/m³ to 73 µg/m³), indicating a broader regional shift beyond the Capital.

The trends, however, remain uneven. Bulandshahr in UP saw a sharp decline from 95 µg/m³ in 2021 to 45 µg/m³ in 2025, while Ghaziabad and Gurgaon recorded moderate reductions. Bharatpur stands out as a persistent high-ozone location, recording annual averages of 81 µg/m³ in 2023 and 84 µg/m³ in both 2024 and 2025.

Nitrogen dioxide and carbon monoxide, largely linked to sources of combustion such as vehicles and industry, show relatively different trends. While they also exhibit seasonal variation, long-term data indicate a gradual decline in their concentrations since 2015.

The long-term data for Delhi show that PM2.5 levels have declined from about 117.5 µg/m³ in 2015 to 96.4 µg/m³ in 2025, while PM10 has fallen from around 244 µg/m³ to 197 µg/m³ over the same period. Although this indicates progress, both pollutants remain far above national and global safety limits.

The persistence of PM10 has been a key concern as well. Even in recent years, coarse particulate matter has dominated pollution levels across days, pointing to the growing role of dust from construction, road surfaces and open land.

This April, PM10 emerged as the dominant pollutant on a majority of monitored days – 52% – across NCR.

Further, data revealed that Delhi’s AQI is closely tied to the wider NCR, as cities like Ghaziabad and Gurgaon continue to record high particulate levels.

While Delhi recorded a year-on-year improvement, with PM2.5 falling from 77 µg/m³ in April 2025 to 68 µg/m³ in April 2026 and ‘Poor’ AQI days halving from 20 to 10, surrounding cities recorded worsening trends.

The PM2.5 levels rose sharply in Hapur (36 µg/m³ to 67 µg/m³), Meerut (55 µg/m³ to 84 µg/m³), Gurgaon (73 µg/m³ to 92 µg/m³), Ghaziabad (81 µg/m³ to 99 µg/m³ ), and Noida (53 µg/m³ to 66 µg/m³ ).

This April, the highest PM2.5 levels were recorded in Ghaziabad (99 µg/m³), Gurgaon (92 µg/m³), and Faridabad (82 µg/m³ ), all higher than Delhi’s average for the month.