Air pollution levels in most Indian cities exceed national standards and international guidelines, with the least polluted cities in the country surpassing the World Health Organization’s safe limits, an analysis of data from a government programme showed on Wednesday.

The report released by Respirer Living Sciences and Climate Trends analysed the five-year performance of the Centre’s National Clean Air Programme. The programme was aimed at reducing average particulate matter concentrations by 2026 in 131 cities.

When it was launched in 2019, the aim was to reduce pollution by 20% to 40% by 2024 in these cities. However, the deadline was shifted to 2026. The government had allocated a budget of Rs 9,631 crore for the programme.

“A five-year status check of the NCAP’s progress reveals a mixed scenario,” the report said. “For 49 cities, PM2.5 data was available for all five years. Out of these, 27 cities recorded improvements in PM2.5 levels from 2019 to 2023. Similarly, for PM10, data across five years was available for 46 cities. Of these, 24 cities saw an improvement in their PM10 levels.”

PM2.5 is particulate matter with a diameter of less than 2.5 micrometres, which can enter the lungs and the bloodstream, while PM10 is particulate matter with a diameter of 10 micrometers or less. The concentration of these pollutants in the air determines the air quality of a place.

The concentration – a measure of how much of the substance is present in the air – is measured in micrograms per cubic metre (µg/m³).

The analysis found that 18 of the 20 most polluted cities under the National Clean Air Programme were in the Indo-Gangetic Plain, “underscoring the region’s vulnerability to heightened particulate matter concentrations”.

“Conversely, only Guwahati and Rourkela, outside the IGP, secured positions among the 20 most polluted cities for PM2.5,” the report said.

In 2023, Delhi recorded the highest PM2.5 levels of 102 µg/m³, an increase of 2.5% compared to 2022. The national capital showed a marginal improvement of 5.9% from its levels in 2019, the report said.

“Patna exhibited the highest PM10 levels in 2023 at 212.1 µg/m³, up from 191.6 µg/m³ in 2022,” it said. “The city has seen 5.8% deterioration in its PM10 levels from 2019.”

The analysis also showed that Silchar in Assam recorded the lowest PM2.5 levels in 2023 at 9.6 µg/m³. Six of the eight least polluted cities recorded improvements in PM2.5 levels between 2022 and 2023, while four of seven cities recorded improvements in PM10 levels, the report said.

However, it also said that when the levels of the least polluted cities in India are compared to the World Health Organization’s annual average safe limit, they all surpass the threshold.

Silchar’s PM2.5 levels are nearly double the global health body’s stipulated safe limit of 5 µg/m³, the report said.

This highlights the ongoing challenges in achieving internationally recognized air quality standards, it added.