Delhi’s NO2 levels 3 times the safe limit at hot spots
Delhi's nitrogen dioxide levels have soared to three times the safe limit, contributing to a worsening air quality crisis amid hazardous PM2.5 and PM10 levels.
Nitrogen dioxide levels in Delhi have surged to three times the national safe limit at multiple locations since November 1, adding a new dimension to the Capital’s air quality crisis as PM2.5 and PM10 concentrations also remained in hazardous levels on Friday.
The hourly NO2 concentration peaked at 240µg/m³ at the IGI Airport (T3) station under the India Meteorological Department, according to Central Pollution Control Board data analysed by think tank Envirocatalysts. This is three times the CPCB’s national safe standard of 80µg/m³ and nearly 10 times the World Health Organisation’s stricter limit of 25µg/m³.
ITO, a key traffic intersection, recorded 221µg/m³, while North Campus, Delhi University – another high vehicular emissions hotspot – touched 210µg/m³. Lodhi Road (181µg/m³), Mundka (178µg/m³) and JLN Stadium also reported elevated readings.
“We have seen ITO consistently record high NO2 levels, which is a fairly busy intersection. The station is also located next to the road and is likely to capture a significant chunk of the emission released by vehicles, which is what people on the roadside are also likely inhaling,” said Sunil Dahiya, founder and lead analyst at Envirocatalysts. High emissions at the airport result from a combination of aircraft and vehicular emissions, he added.
Prolonged exposure periods
Several monitoring stations have recorded prolonged periods when NO2 concentrations stayed above safe levels. Since November 1, IGI Airport recorded 132 hours of exceedance, followed by 128 hours at North Campus, 118 at Najafgarh, 93 at Mundka, and 81 at Lodhi Road. At Okhla Phase-II, levels stayed above the 80µg/m³ mark for 75 hours, while Anand Vihar reported 71 hours of breach.
Experts said the primary sources of NO2 include vehicular emissions, biomass burning and industrial activities, with traffic congestion emerging as a key factor. Vehicular pollution contributes up to 81% of the city’s total NO₂ emissions, making it a key factor to address.
Dahiya said while focus typically remains on particulate matter at this time of year, gases like NO2 can also spike significantly when meteorological conditions are unfavourable. “At intersections, or even around industries, if winds do not blow and temperatures remain high, the hourly peaks can be even higher,” he said.
Elevated NO2 levels exacerbate asthma and respiratory infections, while short-term exposure can cause wheezing, coughing and difficulty breathing.
Mukesh Khare, an expert from IIT Delhi, said vehicles remain the primary source in Delhi, but while meteorological conditions are far better in summer – allowing ventilation and dispersion – they become adverse in winter months.
“NO2 is primarily released when petrol is burnt and is a sign of high congestion or road traffic. We also see aircraft releasing a lot of NO2, so it is no surprise it is high near the airport,” Khare said. In summer, NO2 typically reacts under sunlight and releases hydrocarbons, but with reduced sunshine and low wind speed in winter, accumulation is higher.
“If winds do not blow and there is poor ventilation with not enough sunshine, there is even more accumulation in the hotspot,” he said.
Data gaps persist
Out of 155 monitored hours since November 1, Lodhi Road had missing data for 52 hours, followed by 28 hours at Sonia Vihar and 13 at Patparganj. Of Delhi’s 39 active ambient monitoring stations, 23 had complete data, while the rest showed at least an hour of missing NO2 readings, the analysis found.
An HT analysis of air quality data from the city’s 39 active ambient air quality stations on November 5 had revealed missing data, suspicious measurement patterns and algorithmic loopholes in how the city’s average AQI is calculated. It had flagged how these factors combine to produce readings which may not accurately reflect ground conditions – meaning the actual AQI may be even worse.
