Amid spike in pollution, Delhi’s high NO2 levels a sign of worry

NO2 comes largely from vehicle emissions, and its levels indicate an enduring problem with Delhi’s air — pollution from vehicles.

Delhi’s high particulate matter (PM) 2.5 concentration may be the focus of agencies and government departments as they look to bring down the Capital’s high pollution levels but the concentration of another pollutant, nitrogen dioxide (NO2), is slowly beginning to spike and is currently two-to-three times the permissible limit of 80 micrograms per cubic metre (µg/m3) in parts of the city, Central Pollution Control Board (CPCB) data showed.

Heavy smog in New Delhi on Tuesday. (Raj K Raj/HT PHOTO)

NO2 comes largely from vehicle emissions, and its levels indicate an enduring problem with Delhi’s air — pollution from vehicles.

According to the Delhi economic survey 2022-23, there are 7,917,898 registered vehicles in Delhi. In addition, Delhi also sees vehicular traffic from Gurugram and Faridabad (in Haryana), and Noida and Ghaziabad (in Uttar Pradesh).

It should come as no surprise, then that ITO , one of Delhi’s busiest traffic intersections is currently recording the highest NO2 levels in November, averaging an NO2 concentration of 191µg/m3, over twice the daily safe limit.

Another high-traffic zone, Nehru Nagar (123 micrograms per cubic metre) has the second highest concentration in the month, followed by Okhla Phase-2, which recorded an average NO2 concentration of 116µg/m3.

CPCB data also showed Delhi’s average NO2 concentration in the first seven days of the month has risen sharply, exacerbated by the prevailing calm wind conditions since November 2.

Delhi’s average NO2 concentration in the first week of November was 54.7µg/m3 — a rise of around 47% from last month’s average NO2 concentration of 37.3µg/m3.

Even though the 24-hour concentration is lower than the national standard of 80, the average concentration in November is still over two times the World Health Organization’s (WHO) limit of 25µg/m3.

Experts say long-term exposure to high NO2 levels is linked to asthma and also increases people’s susceptibility to respiratory infections.

Sunil Dahiya, analyst at the Centre for Research on Energy and Clean Air (CREA) said the data clearly shows for a need to have sustained plans for busy intersections, where levels are shooting up to around three times the standard.

“ All three hotspots have heavy traffic and face congestion, with Okhla having industries too, another NO2 source. Government bodies need to look at monthly data and take action at such intersections so that such levels can be brought down,” Dahiya said.

Dahiya added that NO2 levels, similar to PM2.5, was beginning to spike, due to the prevailing calm wind conditions in the city, which were not allowing it to disperse.

The NO2 being emitted by vehicles is therefore remaining close to the surface and accumulating -- to levels beyond permissible limits at locations where congestion is more common.

Data trends for Delhi were similar in October. ITO recorded an average NO2 concentration of 102µg/m3 in the month of October. Okhla Phase-2 recorded 80µg/m3.

In an analysis, released on November 5, the Centre for Science and Environment (CSE) also commented on the rising NO2 levels in the city, pointing out that these were up by around 60% in comparison to the first week of October.

Anumita Roychowdhury, executive director, research and advocacy at CSE, said high NO2 levels in an area were a clear indicator of the impact of vehicular traffic.

“Vehicles are a major contributor of the NOx load in Delhi. The levels are particularly high in heavy traffic areas, and this further reinforces the need for urgent action to reduce vehicular pollution which has become the source of high toxic exposure. In terms of local traffic hot spots, we also need local interventions for more efficient traffic dispersal,” she said.