How accurate are Delhi’s air quality monitoring stations: A ground reality

As winter sets in across India, it brings along poor air for the residents of Delhi. It is caused by a combination of vehicle emissions, industrial activities, construction dust, and burning of agricultural waste in neighbouring states.

During the winter months, particularly from October to February, the pollution worsens significantly, prompting the authorities to enforce emergency measures such as the Graded Response Action Plan (GRAP).

As of 2 pm on Thursday, October 16, the overall air quality in Delhi was recorded in the poor category at 243, according to data from the Central Pollution Control Board (CPCB).

Meanwhile, several areas, including Anand Vihar and Patparganj, recorded air quality in the 'very poor' category, with AQI levels soaring above 300.

On Tuesday, the Central Air Quality Management (CAQM) imposed Stage 1 measures under the GRAP across Delhi-NCR after the AQI was recorded at 211, categorising it as ‘poor.’

The AQI is a measure of dangerous pollutants in the air, such as carbon monoxide, sulfur oxides, ozone, nitrogen dioxide, and particulate matter (PM2.5 and PM10 particles), on a scale of 0 to 500, where a higher number indicates worse air quality and greater health risks.

The governing bodies monitor air quality region-wise. In India, three key regulating agencies are in charge of data calculation and processing they are the Central Pollution Control Board (CPCB), the Delhi Pollution Control Committee (DPCC), and researchers at the Indian Institute of Tropical Meteorology. The air monitoring process is substantially the same for all of these institutes.

Pollutant concentration data are gathered from monitoring stations. Currently, India has two types of ground-based monitoring stations: manual and continuous ambient air quality monitoring stations (CAAQMS).

The primary distinction between them is the time period. While the turnaround time of AQI computed via manual monitoring stations is around eight hours and is mostly utilised for chemical analysis, the CAAQMS provides real-time AQI used across the country for public information.

How Accurate Are Delhi’s Air Quality Monitoring Stations?

A recent Comptroller and Auditor General (CAG) report tabled in the Delhi Assembly expressed concern regarding the location of AQI monitors. The audit of the 24 CAAQMS under the DPCC revealed that 13 of them were not located in accordance with CPCB criteria. The investigation stated that these sites were either too close to trees, roads, high-rise structures, or unpaved surfaces, all of which could distort data.

According to Sunil Dahiya, founder and lead analyst at Envirocatalysts, 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,” Dahiya was quoted as saying by the Hindustan Times.