Exclusive: Delhi AQI data is unreliable – air monitors flout norms, blocked by trees

Do you keep tabs on air quality index data on more polluted days? If you are in Delhi, there is a chance that the numbers may not be real.

In an exclusive investigation spanning 25 real-time air quality monitoring stations across the national capital, Newslaundry found that at least 22 monitors are located or placed in violation of guidelines put in place by the country’s nodal agency on pollution – casting doubts over the accuracy of data they generate.

The capital has 48 air monitoring stations, of which 38 are continuous ambient air quality monitoring stations capturing pollution levels in real-time with minimal human interference. The remaining 10 are manual or ambient air quality monitoring stations, where air samples are collected over a few days and are manually taken to laboratories for analysis.

All of the 38 real-time monitors were placed across the city between 2010 and 2018 – 24 by the Delhi Pollution Control Committee, eight by the India Meteorological Department, and six by the Central Pollution Control Board. 

Newslaundry visited 25 of these continuous ambient air quality monitoring stations, or CAAQMS, including 21 DPCC and four CPCB monitors. But most of these were either surrounded by obstructions like trees, buildings or were in close vicinity of pollution sources in violation of the guidelines issued by the CPCB, which functions under the environment ministry. 

Usually housed in schools, colleges, and stadiums, most of the stations are either tucked away in a corner or set up along a boundary wall and are easy to miss. While the geographic coordinates of the IMD monitors are in the public domain, Newslaundry filed RTI applications to find the exact location of the DPCC and CPCB stations. Armed with a camera and a measuring tape, we had tried to visit 28 monitoring stations covering the length and breadth of the capital. But we were denied entry at the Patparganj and Sonia Vihar DPCC stations and the coordinates of the Mundka monitoring stations shared by the Delhi committee led us to a wastewater stream in Nangloi.

Data captured by these stations is the basis of most policy decisions on combating toxic air — not only in Delhi but across India. 

The violations: ‘Influence definite but unclear’

While CPCB guidelines prescribe that pollution sampling inlets, mounted on top of the monitoring stations, should be at least 20 metres away from trees, barring three, all of the 25 stations surveyed were enclosed by vegetation or buildings. The stipulated distance ensures an unobstructed airflow, but most of the stations had trees planted within a 20-metre range with branches hanging over the sampling inlets at some.

At least five of the stations have been installed close to a busy road, violating the CPCB norm of having monitoring locations at least 50 metres away from a highway or road. This limit was imposed to ensure that a station’s data is representative of different sources of pollution rather than just one or two. 

Alarmingly, at least four monitoring stations run by the CPCB itself did not comply with its own guidelines. For example, at the premises of a government school in Shahpur Jat in south Delhi, a four-storey building towers above the CPCB station set up barely 2.7 metres away. According to the guidelines, the distance between the sampler and a building or any other obstruction should be at least twice the height of the obstacle. 

Experts warn that such flouting of norms compromise the veracity of data on air pollution.

Leading air pollution expert Sunil Dahiya warned that a building near an air monitoring station may either block the wind or trap pollutants near it. “The obstruction would influence the pollution data,” said the founder and lead analyst at Envirocatalysts — an advocacy group on the environment.

Another expert seconded Dahiya. “If they (CAAQMS) are not sited where they should, the data won’t be representative of the area. It creates an overall bias in the reporting of the data. Considering the minimum number of stations, they should comply with the norms,” said Sachchida Nand Tripathi, dean of Kotak School of Sustainability, IIT-Kanpur. 

Reviewing visuals of the monitors photographed by Newslaundry, former DPCC additional director Dr Mohan P George said that most air monitoring stations do not seem to comply with CPCB norms. “Any interference would definitely influence the pollution data. However, there is no certainty if pollution levels would go up or come down. For example, if there are trees that shed more pollen, the station near them could show more pollution,” he said.

George, now a consultant on clean air and sustainable mobility at the Centre for Science and Environment, recalled pitching the relocation of at least five stations with other officials at DPCC before he retired in 2022. The five stations were chosen for their close proximity to a pollution source or the coming up of an obstruction such as a building or trees near it. “When we had selected the sites in consultation with the CPCB, they more or less complied with the guidelines,” he said.

A CPCB official said relocation discussions “keep happening”, without revealing the last time such a topic came up. But nothing has materialised yet, they said. 

It’s not easy to relocate stations, according to the official. “When (relocation) proposals are debated, then the next question emerges: Where can we find a new and better place for installation? Considering this, such discussions die down. Across the world, it’s impossible to ensure that stations fully comply with siting guidelines. Once you get the land for stations, you have to compromise with air quality data,” said the official.

When informed about Newslaundry’s findings, the official was not surprised. “Where can you find a place in Delhi where there are no trees within 20 metres? It does not happen. These guidelines are applicable in an ideal world. But we have to look at them realistically. If we say that there should not be any tree within 10 metres. But tomorrow, someone constructs a building, we can’t do much. The land-owning authority is free to do whatever they want with their property.”

According to the CPCB, a city with more or equal than 5 million people should have at least 16 CAAQM stations. Delhi, with the current population of 33 million, going by the CPCB’s guideline, is short of 68 such stations even when the capital has more stations than any other state or UT. Though the union ministry of environment, forests and climate change recently informed the National Green Tribunal that it had no plans to add more CAAQMS to Delhi’s network. 

IIT-Kanpur’s Tripathi believes that low-cost sensors could meet the shortfall with their hyper-local focus in capturing air pollutants. One CAAQMS typically costs “Rs 1 crore” compared to Rs 50,000 for a sensor. 

Here are some of the worst violators of the 25 monitoring stations we were able to visit.

Jahangirpuri (DPCC)

This station was among the second-generation monitoring stations that were installed in 2017. Located on what was then unoccupied space at a government Industrial Training Institute, this station now stands under the shadow of a ground-plus three-storey building that came up just seven metres away in 2022. The distance between the sampler and the building should have been greater, as per the CPCB norms.

The building, which blocks the southeast airflow to the station, prompted George and his DPCC colleagues to propose relocation of some stations.

Narela (DPCC)

A grove of trees, some of which stand tall within a 10 metre-range, block the Narela air monitor from three sides. A few trees also hang over the station as the area around it remains unkempt with wild shrubs.

Making matters worse, a one-storey structure stands just 10 metres away from the station’s sampling inlet— complying with the building distance norm.

Anand Vihar (DPCC)

This monitor is located near one of the exit points at the bustling Anand Vihar Interstate Bus Terminal. Experts warn that instead of capturing ambient air, this station mostly captures key pollutants from road dust and tail pipes.

“This defeats the purpose of measuring the ambient air. Ideally, the stations should be away from the source of pollution,” said Mukesh Khare, professor emeritus at IIT Delhi’s civil engineering department.

Despite the risk of compromised readings, several stations, such as the CPCP air monitor at ITO, have been installed close to busy roads.

Bawana (DPCC)

Located behind the Maharishi Valmiki hospital, this station abuts a park and has tree thickets enclosing from two sides, with the nearest sapling at just a 6.6 metre distance. 

Meant to capture industrial pollutants, the plant stands just a few metres away from a sewage treatment plant.

Punjabi Bagh (DPCC)

Located in Sarvodaya Kanya Vidyalaya, the station is covered by trees from three sides with one tree partially hanging over it. The monitor has been set up close to the school boundary wall and just 10 metres from a road running by posing the risk of capturing more vehicular and dust pollution. 

The DPCC air monitoring stations in RK Puram, Najafgarh and CPCB stations in Dwarka and Rohini are also covered by a dense growth of trees. 

It is important to note that even norms prescribed by the World Health Organisation (WHO) that air stations should not be located in carbon sinks or areas with dense vegetation. 

While the presence of buildings and vegetation have given rise to demands of relocation of air stations, with the Delhi government reportedly mulling shifting some, some experts have raised concerns with this approach. 

“Each station contains data on trends for years and years. Once stations are relocated, we will lose such data points,” warned Dipankar Saha, former head of CPCB’s air laboratory division. He said that instead of relocating stations, authorities should set up more air monitors.

Newslaundry reached out to CPCB and DPCC with a list of questions on several monitoring stations not complying with the guidelines. This report will be updated if we receive a response.

A pattern: Close to boundary

Most structures or trees have come up only after installing stations, said the CPCB official quoted above. 

For example, at Shahpur Jat, the CPCB station was overshadowed by a ground-plus three-floor building at a distance of just 2.7 metres. The distance should ideally have been greater.

A Google Earth image shows that the construction began somewhere around 2019 — around “three-four” years after the installation. Besides, the station, located in a government school, was covered with trees from two sides. “Delhi is a built-up city. So new structures are bound to come up,” said George.

At RK Puram, the station was overshadowed with a fully-grown banyan tree from behind. When the station was installed around 2010, the tree was also planted. The station, located in a Kendriya Vidyalaya school, is covered with trees from two other sides. The nearest tree was 2.5 metres.

Another pattern that Newslaundry saw during its visits was that most stations were assigned to only corners of the institutes or stadiums, bringing them closer to the boundary wall and thereby to road pollution. 

DPCC’s stations at Dwarka (CSIR-NMIR), Anand Vihar, Punjabi Bagh, Pusa and Wazirpur, and CPCB’s ITO station, were close to the road. Most of them were found occupying the most unnoticeable part of the property. “No land-owning authority would give us prime property. We mostly get the most unusable site at the property,” said the CPCB official quoted above.

This piece is part of a collaborative campaign to tackle air pollution. Here’s how you can join the Fight To Breathe. Click here to power this campaign.