Delhi’s 6 new air stations may give pollution data green bias: Experts

The Delhi environment minister has announced the locations for the five stations but not disclosed the location for the sixth

Last week, Delhi environment minister Manjinder Singh Sirsa announced that the government will add six new continuous ambient air quality monitoring stations (CAAQMS), adding to the Capital’s 40 station-strong grid that acts as the backbone of the city’s pollution monitoring mechanism.

Delhi minister Manjinder Singh Sirsa. (ANI)

But three of the new stations are proposed to be inside lush-green campuses – Jawaharlal Nehru University (JNU) in south Delhi, Indira Gandhi National Open University (IGNOU) in south Delhi and Netaji Subhash University (West Campus) in west Delhi – one station deep inside the Central Ridge at the ISRO Earth station near Malcha Mahal, and two more in relatively green areas, Delhi cantonment and the Commonwealth Games Sports Complex in east Delhi, HT has learnt.

Sirsa has announced the locations for the five stations but not disclosed the location for the sixth.

Experts say the location chosen for these new stations may eventually bring the overall average air quality index (AQI) of the city down, thereby providing a lopsided picture of pollution in the city, especially in the winter months.

Anumita Roychowdhury, executive director at the Centre for Science and Environment (CSE), echoed the concern. “These sites are not data-starved zones. We need monitors in southwest and northwest peripheries where coverage is inadequate.”

Sirsa, however, rejected the criticism, stating Delhi’s ambient air quality network needed to be expanded to cover all types of locations. “We already have monitors in several polluted hotspots. If we keep adding only to those, we won’t have a true citywide picture,” he said. “The new sites were selected by DPCC, and the process began under the previous government.”

Data reviewed by HT reveals that in five of the six announced locations, the nearest existing stations already report lower AQI levels than the city average. At Netaji Subhash University’s West Campus, the nearest monitor at Najafgarh recorded an AQI of 184 (moderate) on Friday, compared to the city’s average of 258 (poor). Similarly, the stations closest to JNU and Delhi Cantonment — both monitored by the RK Puram CAAQMS — reported an average AQI of 246. Aurobindo Marg, the nearest station to IGNOU, reported 183. Mandir Marg, closest to the planned ISRO Ridge site, stood at 154.

Only one site — the Commonwealth Games Village — had a nearby monitor (Patparganj, AQI 307) that exceeded the city average.

Delhi currently has 40 AQI stations that provide critical information that help authorities and planners decide on pollution mitigation measures, especially when plumes of noxious air engulf the Capital in the winter months.

Out of these 40, at least 10 are broadly representative of industrial areas including Mundka, Bawana, Wazirpur and Jahangirpuri. At least seven are in relatively green areas, including Lodhi road, Dr Karni Singh Shooting Range and IHBAS (Dilshad Garden). At least eight are in residential areas, including Punjabi Bagh, Rohini, RK Puram and Pitampura. The remaining stations such as ITO, Burari Crossing and Nehru Nagar represent traffic intersections and commercial spaces in the city.

Experts pointed out that the locations selected for the six new stations don’t represent this mix, and said that all land-use types – ranging from residential, industrial, commercial and green areas – needed to be covered for an accurate representation of Delhi’s ambient air.

“The location of a station plays a crucial role in the days being gathered round-the-year. Incorrect locations — either too close to a busy road, or too far, means the data is not an accurate representation of the ambient air,” said IIT Delhi professor Mukesh Khare, an air pollution expert.

Khare said existing stations deep inside institutes or campuses – such as that as in IHBAS – have little vehicular emissions or major pollution sources around them. “Thus, their PM 2.5 and PM 10 levels will be comparatively lower,” Khare said, seeking more transparency from the government on the criteria on which these new locations were selected.

Delhi’s average AQI comes from the average AQI of the day of each of the 40 stations installed. However, on any given day, the difference in AQI from the worst and least polluted locations in the city can be over 100 points.

For instance, on Friday, the highest AQI in the city was recorded at Wazirpur (373) -- an industrial hub, followed by Rohini (334), a busy residential area. The lowest AQI in comparison was 156, at Mandir Marg, followed by a reading of Aurobindo Marg (183) and 184 at Lodhi road.

All three lowest AQI readings came from stations in relatively green areas, away from the main road. For instance, at Aurobindo Marg, the monitoring station is installed deep inside the campus of the National Institute of Tuberculosis and Respiratory Diseases, around 1.5kms away from the Aurobindo Marg main road.

Delhi Pollution Control Committee (DPCC) and the environment department officials did not comment on the selection criteria for these stations.

24 out of the 40 stations are run by DPCC with the remaining 16 by the Central Pollution Control Board (CPCB), the India Meteorological Department (IMD) and the Indian Institute of Tropical Meteorology (IITM). This includes six under CPCB, eight IMD and two under IITM. All six new stations will be under DPCC.

A recent Comptroller and Auditor General (CAG) report tabled in the Delhi Assembly on April 1 also flagged concerns about the placement of AQI monitors. The report, which carried an audit of the 24 CAAQMS under the DPCC, found 13 of these were not located as per CPCB guidelines. These stations were either too close to trees, roads, high-rise buildings, or unpaved surfaces, which could distort readings, the report said.

Stations at Anand Vihar and Wazirpur, for instance, were near major roads, while those at Civil Lines and Okhla were close to construction sites. The CAG report also raised concerns that incorrect placement of these stations could lead to unreliable pollution data, ultimately affecting air quality assessments and mitigation policies.

Sunil Dahiya, founder and lead analyst at Envirocatalysts, said the city urgently needs better, not just more, data. “The new stations should be installed in commercial, residential, and industrial areas to improve the representativeness of the grid. Focusing too heavily on green areas will skew the numbers.”

To calculate the AQI for any monitoring station, the CPCB calculates sub-indices for eight individual pollutants (PM10, PM2. 5, NO2, SO2, CO, O3, NH3, and Pb) at the location using its 24-hourly average concentration value (8-hourly in case of CO and O3). The worst sub-index is the AQI for that location. The average AQI for each station is then used to compute an average AQI of the entire city.