Delhi: Slow winds, fog keep air pollution in severe zone

Delhi’s air quality has deteriorated to the “severe” category once again, with the Capital’s average air quality index (AQI) hitting 406, according to the Central Pollution Control Board’s (CPCB) daily 4pm bulletin on Friday. The city’s air had already deteriorated to the brink of the “severe” category by Thursday afternoon, before slipping into deep red later that evening.

While the Delhi government had banned construction activities in the Capital from Thursday on the orders of the Supreme Court, calm winds and low temperatures trapped pollutants. Delhi also saw shallow fog in the morning, which mixed with pollutants to cause smog, the India Meteorological Department (IMD) said.

RK Jenamani, scientist at IMD, said calm winds were recorded over Delhi till 1pm, with wind speeds only picking up between 1pm and 4pm. “From 4pm onwards, they dipped again. Visibility at Safdarjung [airport] remained between 300 and 500 metres till 10am, after which it marginally improved to 800 to 1,000 metres. This can be attributed to smog coverage and after the November 11-13 smog spell, this is the second such spell this month where such poor visibility has been recorded at the airport,” he said.

According to the System of Air Quality and Weather Forecasting And Research (Safar), relief is expected from November 29 onwards, when surface winds touch 15-20 km/hr.

“Local surface winds are likely to increase slightly for the next two days, which will increase dispersion of pollutants, leading to slight improvement, but AQI will still remain in the higher end of the ‘very poor’ category. Mixing layer height and wind are the dominant factors controlling air quality, but from 29th, significant improvement in AQI is expected due to high wind speed,” it said.

Delhi recorded a maximum temperature of 27.6 degrees Celsius on Friday, while the minimum was 11 degrees. Temperatures are expected to dip below 10 degrees once again only after November 30, when cold northwesterly winds start blowing towards the Capital. Saturday’s forecast shows a maximum and minimum of 27 and 10 degrees Celsius respectively, with shallow fog expected in the early hours.

Tanushree Ganguly, programme lead at the Council on Energy, Environment and Water (CEEW) said forecasts need to be considered while announcing mitigation measures and relaxing them.

“The air quality in Delhi has dipped to ‘severe’ category over the last two days, especially during the morning and evening time. This is primarily due to lower wind speed and temperature, which prevent the dispersion of pollutants. According to forecasts, the transport sector is the leading local contributor to Delhi’s air pollution. Just like the Delhi government has restricted the entry of diesel commercial vehicles, it should continue to actively consider forecasts before relaxing restrictions within the city,” she said.