Delhi’s air in January was choked not only by particulate matter but also by elevated levels of nitrogen dioxide, cancer-causing benzene and other toxic pollutants, with official data showing repeated breaches of safety limits across large parts of the capital.

An analysis by EnviroCatalysts, an independent research body, based on monthly average air quality data till January 25, found that nitrogen dioxide levels exceeded recommended limits for more than 25 days at most monitoring stations in January. This occurred even though some locations recorded lower concentrations compared to the same period last year.

The analysis also showed that benzene, a known carcinogen, crossed the World Health Organization’s guidelines on 24 days during the month. The WHO states that no level of benzene exposure is considered safe.

Long-term exposure to benzene is linked to a higher risk of leukaemia and other blood cancers, public health experts have warned.

The data further indicated that benzene breached India’s annual safety standard of five micrograms per cubic metre on one day in January, highlighting continued exposure risks despite seasonal improvements in overall air quality.

In comparison, during the same period last year, benzene levels breached the WHO guidelines on 28 days but did not exceed the Indian standard on any day.

EnviroCatalysts is an environmental research organisation with a focus on data-driven solutions for air pollution, energy transition, and industrial decarbonisation.

Under the WHO guidelines, nitrogen dioxide should not exceed 25 micrograms per cubic metre over 24 hours, while the Indian National Ambient Air Quality Standards prescribe a higher limit of 80 micrograms per cubic metre for a 24-hour period.

The analysis found that large parts of Delhi continued to record elevated nitrogen dioxide levels through January.

The analysis showed that several locations witnessed steep increases. Burari Crossing recorded 96 micrograms per cubic metre, compared to 15 in January last year; Okhla Phase II saw nitrogen dioxide rise sharply to 108 from 49 a year ago; while Wazirpur emerged as the worst-affected station, recording 135 micrograms per cubic metre, up from 84.

The other areas with elevated levels, according to the analysis, included Mandir Marg at 93 compared to 100 last year, Jahangirpuri at 86 compared to 55, Najafgarh at 77 compared to 52, and North Campus, Delhi University, at 70 compared to 43 last year.

The data also showed that the IGI airport’s Terminal-3 recorded 62, compared to 45 a year ago, IHBS Dilshad Garden 56 compared to 30, NSIT Dwarka 52 compared to 35, while Pusa recorded 71 compared to 47 in the same period last year.

However, Alipur recorded 37 micrograms per cubic metre, down from 57 micrograms per cubic metre in January last year.

According to the analysis, Anand Vihar recorded 38, down from 79, while Ashok Vihar saw 52, compared to 60 earlier. Aya Nagar recorded 34, down from 41, and Bawana recorded 22, compared to 33 last year.

While the central and residential areas showed relative improvement, the analysis noted that they remained above the safe thresholds on most days.

According to the study, ITO recorded 51 micrograms per cubic metre as compared to 100 last year, Lodhi Road recorded 32 against 94, Punjabi Bagh 39 compared to 61, Rohini 36 compared to 55, Siri Fort 26 against 33, while Sonia Vihar recorded 37 compared to 47 in the year-ago period.

Overall, around 39 per cent of the monitoring stations recorded higher nitrogen dioxide levels in January compared to last year, even as the others showed a decline, the analysis said.

The analysis showed that nitrogen dioxide levels crossed the safe limits on more than 25 days this January, though lower than last year, when all 31 days of the month breached the standard.

“It is easy to understand the reason behind the sources of pollution in some of these emerging hotspots, be it industrial zones or transport activity. However, the vicinity of some stations may be compromised due to the presence of a dense tree canopy or tall buildings in close proximity.

“Such stations may record higher or lower levels of pollution compared to giving a true representation of the area. It is necessary to conduct an audit of all the monitoring stations,” Sunil Dahiya, Founder and Lead Analyst, EnviroCatalysts, said.

The other gaseous pollutants showed mixed trends, the analysis found.

Carbon monoxide breached Indian standards on three days in January, compared to no breaches during the same period last year.

The carbon monoxide standard is assessed on an eight-hour basis, unlike the 24-hour standard applied to several other pollutants.

Sulphur dioxide, ozone and ammonia remained within the prescribed limits throughout the month.

According to the study, other sources contributed 28.6 per cent to the overall pollution load, with Delhi’s transport sector alone accounting for 15.1 per cent, making vehicles the single-largest identified contributor.

Experts cited in the analysis attributed the pollution to vehicular emissions, industrial activity and power plants, road dust and construction, biomass and waste burning, and the use of solid fuels and diesel generator sets in households and commercial establishments.

Health experts quoted in the analysis warned that prolonged exposure to these pollutants can damage the lungs and heart, aggravate asthma, increase the risk of respiratory infections, heart attacks and strokes, and, in the case of benzene, raise long-term cancer risks.

Despite marginal improvements at some locations, the analysis concluded that Delhi’s air in January remained heavily polluted, with residents continuing to breathe air that frequently exceeded both Indian and global safety limits.