Rain cleared Delhi's air for a day, but experts warn the pollution has not gone

Delhi breathed easier this weekend, but scientists and forecasters say the relief brought by two nights of thunderstorms is unlikely to last, and that the rain has done little about where the capital’s dirty air comes from.

The city’s air quality index (AQI) stood at 167 at 9 am on Sunday, in the moderate category, according to Central Pollution Control Board data. Yet 11 of the 54 monitoring stations were still in the poor range, led by IIT Delhi at 245 and Alipur at 233.

The Air Quality Early Warning System for Delhi expects the air to stay in the poor category from 25 to 27 October and to swing between poor and moderate after that.

Washing out or blowing away

Environmental scientists say the weekend’s improvement says more about the weather than about any fall in emissions. “Rain removes some airborne particles, and strong winds can disperse others,” said Hishmi Jamil Husain, an environmental scientist.

Delhi environmentalist Manu Singh put the difference bluntly. “The critical scientific distinction is between removing pollutants from the atmosphere and merely redistributing them,” he said. Environment consultant Diwan Singh said relying on weather meant “we are focussing on dispersal of pollution, rather than on reducing it”.

Soumya Dutta, a former advisory board member of the UN Climate Technology Centre and Network, pointed to what happened after the rain spell of 10 to 14 October, when the index climbed back to around 300 within days. Without action on large pollution sources inside the city, he argued, each wet spell offers only a pause.

Forecast and festival

S N Mishra of the TERI School of Advanced Studies noted that “an occasional spell of rainfall or thunderstorms in October is relatively rare”. He expects the cyclone now forming in the Bay of Bengal to interact with a western disturbance around 28 to 30 October, which could bring more light rain to Delhi. He sees the air staying mostly moderate, and occasionally poor, until Diwali, when firecrackers could add a heavy load of pollutants. The India Meteorological Department also forecasts light rain over the city on 29 and 30 October.

Curbs stay on

The Commission for Air Quality Management invoked Stage 1 of the Graded Response Action Plan (GRAP) across Delhi-NCR on 21 October, the day the city recorded its first poor air of the season at 245. Stage 1 applies when the AQI is between 201 and 300 and covers dust control at construction sites, curbs on open burning and checks on polluting vehicles. No change to the stage was announced on Sunday.

Environment Minister Manjinder Singh Sirsa has called invoking GRAP this late in the season “unprecedented in recent years”. The government’s 11-point winter plan includes dust control, a push for electric vehicles and identifying local pollution sources, with a command centre tracking construction sites.