Delhi’s air quality remains ‘very poor’; slight rise in mercury

According to the Central Pollution Control Board, the hourly Air Quality Index (AQI) was 372 at 8am on Friday

The fog continued to envelop Delhi as pollution levels remained in the “very poor” category amid a slight rise in mercury. The city is expected to record a maximum temperature of 21°C while the minimum was 9.8°C. On Thursday, the minimum temperature was 9.3°C, two notches below the normal.

The average 24-hour AQI was 371 on Thursday. (Hindustan Times)

According to the Central Pollution Control Board, the hourly Air Quality Index (AQI) was 372 at 8am on Friday. The average 24-hour AQI was 371 on Thursday.

An AQI between zero and 50 is considered good, 51 and 100 satisfactory, 101 and 200 moderate, 201 and 300 poor, 301 and 400 very poor, and 401 and 500 severe. The AQI in the poor category leads to breathing discomfort for most people on prolonged exposure.

The visibility dropped to 500 metres at 8:30am at Safdarjung and Palam on Friday. Moderate fog is expected over the next three days.

The temperatures will start dipping from Saturday. “Cold northwesterly winds will return and both maximum and minimum temperatures will begin to dip. The drop will be gradual from January 14-16,” said an official.

On Thursday, monitoring agency System of Air Quality and Weather Forecasting and Research said fine particles (size < 2.5 micrometer) contributed ~ 60% to PM10.

“For the next 3 days, surface wind speed (12 to 16 km/h) and temperature (Max 17-20 deg C; Min 9-6 deg C) are likely to improve air quality. Mixing layer height is likely to be ~ 1.0 km that causes moderate ventilation of pollutants.”

The air quality was likely to improve but remain within “very poor” due to low temperature, which helps accumulation of pollutants, and moderate surface winds. “Morning fog is likely at isolated places. There is a likelihood of a rain spell on the 13th [Friday] due to cyclonic circulation over the northwest region that helps wash out of pollutants and improve air quality.”