In 2019, average PM2.5 level in Delhi thrice the safe limit, finds study

The study also found Delhi’s urban areas were more polluted than its semi-urban and rural locations, though the difference was only marginal.

An analysis of PM2.5 (particulate matter of up to 2.5 microns size) levels in the National Capital Region (NCR) has shown that the pollutant level in the city is nearly three times the national safe standard through the year, with Shahdara identified as the most polluted district in Delhi.

PM2.5 levels in the Capital in 2019 ranged between 80µg/m3and 130µg/m3 seasonally, as against a safe limit of 40µg/m3. (HT)

According to the study, “Satellite-based Mapping and Quantification of PM2.5 in India” by the Centre for Study of Science, Technology and Policy (CSTEP), PM2.5 levels in the Capital in 2019 ranged between 80µg/m3(microgram per cubic metre) and 130µg/m3 seasonally, as against a safe limit of 40µg/m3. The study showed that Shahdara recorded an average annual PM2.5 reading of 126µg/m3, followed closely by East Delhi (124µg/m3) and West Delhi (122µg/m3). The South-west Delhi district was the least polluted, recording an annual PM2.5 level of 113µg/m3, which is still nearly three times the annual safe limit.

The study mapped daily PM2.5 levels over Delhi-NCR in 2019 using a combination of satellite and on-ground data from monitoring stations, to identify PM2.5 hot spots in a 1km grid at the ground level.

The winter months of January and February recorded the highest average PM2.5 level (134µg/m3), followed by the post-monsoon period of October, November and December (131µg/m3). Summer saw average PM2.5 level drop to 79µg/m3, and even the monsoon months of June, July, August and September (57µg/m3) failing to bring the pollution levels within the safe limit.

The study also found Delhi’s urban areas were more polluted than its semi-urban and rural locations, though the difference was only marginal. “Annually, the urban areas were characterised by the highest average PM2.5 level (109 µg/m3), followed by semi-urban areas (102µg/m3), rural locations (101µg/m3), and the uninhabited parts of Delhi (100µg/m3) areas,” it said.

PM2.5 pollutants can cause several adverse effects to overall climate and human health, particularly in the Indian subcontinent where a large population lives in areas where its level exceeds the safe limit.

Experts say that PM2.5 can vary significantly over short distances, and since pollution monitoring centres are confined to urban areas, they fail to capture fine spatial variations.

“It is difficult to capture the intricate spatial variations of PM2.5 without having an extremely dense network of monitors. Satellite-based products could bridge this gap,” said Dr Sreekanth Vakacherla, one of the authors of the report and a senior research scientist at CSTEP, adding that most air quality stations were currently limited to urban centres.

He, however, said there were challenges and limitations with satellite data too, especially during cloudy days. “Finding the right balance and combination of on-ground and satellite data could be beneficial,” he said.

A Delhi Pollution Control Committee (DPCC) official said that using satellite technology had its limitations, particularly on cloudy days or when a dust-storm is passing over the city. “In a city like Delhi, which has a great network of air quality monitoring stations, satellite technology can be used in combination with existing monitors to create a very fine grid at the ground,” the official said.

Dipankar Saha, former head of Central Pollution Control Board’s (CPCB) air laboratory said pollution control boards and institutions are slowly shifting to other methods to map PM 2.5 levels, which includes low-cost sensors as well.

“We know about the pollution problem in the National Capital Region, but we now need to use this daily data to carry out actions on the ground that can bring about a change, particularly at hot spots,” he added.