A report by the Center for Research on Energy and Air has pointed out discrepancies in India’s air quality data, raising questions about the progress recorded by the National Clean Air Programme.
Published on Friday, the report aimed to analyse variations in PM10 concentrations between integrated data and continuous ambient air quality monitoring stations data in NCAP cities between 2017-2018 and 2023-2024.
For this period, it collected CAAQMS data from the Central Pollution Control Board and integrated data for all 131 NCAP cities from PRANA, or the portal for regulation of air-pollution in non-attainment cities.
According to the report, at the heart of the problem seems to be a clash between old and new technologies while integrating data. Perhaps no city better illustrates this problem than Byrnihat, an industrial town in the northeastern state of Meghalaya. According to continuous monitoring data, Byrnihat had a PM10 concentration of 266 micrograms per cubic metre – more than four times India’s national standard. Yet the integrated data, which combines continuous and manual measurements, showed only 104 micrograms, the report claimed.
The newer system – the CAAQMS – provides real-time, 24/7 data on pollution levels. These automated sentinels have expanded from just 16 cities in 2017-18 to 93 cities in 2023-24, and represent higher precision in pollution monitoring.
Running parallel is the older National Air Quality Monitoring Programme, or NAMP, which relies on manual measurements taken just twice weekly for a total of 104 readings per year. These stations, numbering 966 across 420 cities as of November 2024, provide sporadic snapshots rather than a continuous picture.
“When both datasets are combined to produce daily air quality reports, the resulting assessment may be compromised,” the CREA report warns. This integration of continuous and intermittent data creates what environmental scientists call a “methodological incongruity”.
The report is authored by Manoj Kumar, who is also one of the experts guiding Newslaundry’s campaign to tackle air pollution.
Data variations
For 2023-2024, while CAAQMS reported increases in PM10 levels for 17 cities, integrated data noted increases in 15 cities, the report noted.
CAAQMS also identified 23 cities with a 1 to 10 percent decrease in PM 10 levels, compared to 27 cities in integrated data. CAAQMS data also identified 16 cities with a 10 to 20 percent decrease, versus 12 in integrated data. Both sources reported six cities with a 20 to 30 percent decrease; and CAAQMS recorded one city with a 30 to 40 percent decrease, while integrated data showed two cities in that range.
“The significant variation between this data raises serious questions about data accuracy. These contrasting contributions have raised critical questions about the accuracy of air quality data, suggesting potential inconsistencies that could misrepresent actual improvements,” the report said.
Manoj Kumar, an expert with CREA, explained that the limited number of observations by manual stations makes it difficult to assess long-term air quality trends.
The report noted that the reliance on twice-weekly monitoring by manual stations meant “that pollution peaks or short-term fluctuations which can occur due to specific events such as traffic congestion, industrial activity, or weather changes are likely to be missed”. “The data collected through NAMP may not accurately reflect the pollution levels during the days when monitoring is not conducted. Therefore, the dataset lacks the continuous nature required for high-precision air quality assessments”, it said.
High PM10 levels
PM 10 levels recorded in 2023-2024 in as many as 22 cities were at least twice the limit set under National Ambient Air Quality Standards, according to a report released by the Centre for Research on Energy and Clean Air.
The report also found that the PM10 levels in five cities exceeded thrice the NAAQS limit, set under the National Clean Air Programme, in the same time period.
Overall, 83 cities in India recorded PM 10 levels above the National Ambient Air Quality Standards (NAAQS) of 60 µg/m³, the report found.According to the report, between 2017-2018 and 2023-2024, national capital Delhi featured consistently among the top five polluted cities except for in 2020-2021.
To reduce particulate concentrations in 131 cities, the environment ministry launched NCAP in 2019 and fixed 2025-2026 as the deadline to achieve 40 percent reduction.
Environmentalist Jai Dhar Gupta emphasised the importance of regular calibration for air quality monitors, regardless of whether they are manual or continuous. He said there is a possibility of a sensor drift if not properly calibrated.
In its key recommendations, the report stated that CAAQMS and NAMP data needs to be analysed separately, the integrity of the data needs to be maintained by locating monitoring stations in proper locations and maintaining them adequately, and use both CAAQMS and NAMP methods to measure air pollution in India with a clear plan to convert NAMP stations to CAAQM stations in a time-bound manner.
Newslaundry had earlier found that 25 real-time air quality monitoring stations in Delhi were not compliant with the CPCB’s guidelines.
Newslaundry reached out to the CPCB’s public relation division head, Sharandeep Singh, and Delhi Pollution Control Committee chairman Sanjiv Kumar and member secretary Dr KS Jayachandran for comment. This report will be updated if they respond.
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