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Air quality ‘severe’, moderate fog in parts
The city's average 24-hour air quality index was 411 on Sunday, with pollution levels expected to deteriorate again on December 27.
Delhi’s air quality remained in the “severe” zone for the third straight day on Sunday as weak winds locked in local emissions and extended residents’ exposure to a host of respiratory illnesses.
The Capital on Sunday clocked an average 24-hour air quality index (AQI) of 411 at 4pm, as against 450 on Saturday and 409 on Friday.
The city usually goes through three fortnights where the AQI is routinely in the severe zone: The first half of November, the second half of December, and then mid-January. During the first phase, the toxicity is fuelled largely by smoke from farm stubble fires in Punjab. The second and third phases are, however, down largely to local sources of pollution like vehicular and industrial emissions, which are in turn worsened by nearly still winds and dipping temperatures.
With the pollution also came a coat of smog, which draped parts of the city on Sunday evening. The visibility at Safdarjung fell to 200m in the morning and 300m at 7pm, according to the India Meteorological Department (IMD).
READ | Air worsens further, fog affects flight operations
The minimum temperature, meanwhile, on Sunday dipped to 7.6°C, around normal for this time of year, from a relatively balmy 9.6°C the previous day.
Experts pinned this temperature dip to clear skies. However, the clear skies trapped heat in during the day, pushing the maximum temperature up to 25.9°C, five above normal for this time of the year, and the highest day-time mercury this month.
Clear skies allow in ample sunlight during the day. However, in the absence of any clouds at night, the heat given out by the surface is lost fairly quickly and night-time temperature plummets.
To be sure, dipping day-time temperatures and, consequently, a narrower gap between the maximum and minimum temperature are a more accurate bellwether of the winter’s spread than the night-time value alone.
READ | Delhi air quality 'severe' with AQI 400, GRAP III reimplemented: Gopal Rai
“We saw northerly winds with clear skies, which led to a slight rise in temperature. There was a cloud cover over the city over the past two days because of a western disturbance. However, this was absent on Sunday,” said Kuldeep Srivastava, IMD scientist.
“We are expecting lower temperatures and higher wind speeds over the next couple of days,” said Srivastava.
Officials said that the wind speed was around 8kmph on Sunday.
According to the Central Pollution Control Board’s (CPCB) forecast, Delhi’s AQI will improve marginally over the next two days, before deteriorating again by December 27.
“The air quality is likely to improve and reach the ‘very poor’ category on December 25 and remain in the category on December 26. The air quality is likely to deteriorate again from December 27 as meteorological conditions are extremely unfavourable,” said the early warning system’s air quality and weather bulletin for Sunday.
The CPCB classifies an AQI between 0-50 as “good”, between 51 and 100 as “satisfactory”, between 101 and 200 as “moderate”, between 201 and 300 as “poor”, between 301 and 400 as “very poor”, and over 400 as “severe”.
