Experts warn about rise in NO2 levels across city

While Delhi on Friday recorded the fourth consecutive "severe" day under the air quality index (AQI) - a scale that uses a weighted formula biased towards particulate matter (PM) - experts warned that levels of another dangerous toxin in the air, nitrogen dioxide (NO2), have been consistently soaring, even during periods of relatively "low pollution".

- Jasjeev Gandhiok

The primary sources of NO2, which causes wheezing, shortness of breath and can lead to respiratory infections, include vehicles, biomass burning, and industrial emissions, according to scientists. Traffic congestion is particularly significant, as it results in idling vehicles that release high levels of NO2.

Data analysed by HT shows that NO2 concentrations have frequently breached safety limits in several regions across the city, especially high-density traffic zones like ITO and Anand Vihar.

Data from Central Pollution Control Board (CPCB) showed the hourly NO2 concentration touched a peak of 494 µg/m3 at ITO, which is among Delhi's busiest traffic intersections. This was followed by an hourly peak of 489µg/m3 at east Delhi's Anand Vihar, another traffic hub comprising of an ISBT, a metro station and a railway station.

Not too far behind was west Delhi's Pusa, which touched a peak of 447µg/m3.

These figures are nearly six times the national safety standard of 80µg/m3, with the World Health Organization's (WHO) limit being far stricter at 25µg/ m3. In other words, if you're at ITO or Anand Vihar during poor traffic, you are inhaling as much as six times the safe limit of NO2.