The change was stark on Sunday. With the mugginess making it feel like 45.7 degrees Celsius, the AQI hit 261, a figure not seen in 85 days. Both the IMD and the CAQM say these are the kind of conditions that will hang over the neighbourhoods for a while.
It was an uncharacteristic leap. One day you had an AQI of 140, the next it was 261, putting an end to a month of mostly ‘moderate’ or ‘satisfactory’ readings. You have to go back to April 17 for a number this high, when it was 263.
Why the spike now?
CAQM puts it down to transnational winds carrying mineral dust from storm fronts in Afghanistan, Iran and Pakistan. As the plume made its way into northwestern India and Delhi, PM10 and other coarse particulates followed suit.
Dust and PM10: the mechanics
There is some force behind the movement of this dust across the Indo-Gangetic Plain, the commission says. They do not see the air quality turning any better in the next few days, so much of the city is to be left in the ‘poor’ category until the spell is over.
What authorities decided
Since the pollution is coming from outside, there has been no call for GRAP Stage-I. The CAQM has instead told the Delhi Pollution Control Committee to step up their game on dust control in the city.
To put the numbers in context with CPCB norms: 0 to 50 is good, 51 to 100 satisfactory, 101 to 200 moderate, 201 to 300 poor, 301 to 400 very poor and 401 to 500 severe.
Heat and humidity on the ground
The weather has only made it worse. The IMD put the top of the day at 36.8, 1.3 above what is normal, with the feels-like temperature at 45.7 by 5.30 pm. Humidity was at 64 per cent in the morning and 52 per cent in the late afternoon.
The observatories tell a similar story. Palam was 36.6, Lodhi Road 37, Ridge 36 and Ayanagar 36.2. On the lower end, Safdarjung was 28.3 (a degree over the norm), with 27.1 at Palam, 27.2 at Lodhi Road, 25.6 at Ridge and 27.4 at Ayanagar.
From steady to spiky: the recent pattern
Delhi has been in the ‘moderate’ to ‘satisfactory’ for most of the month, until this about-face. The last time the capital went over 263 was on April 17. This latest turn of events is a case in point for how regional dust can undo local progress in a hurry.
Official figures show Sunday’s 261 was well off the mark from Saturday’s 140.
For Monday, the weather office is calling for some strong surface wind in the day, with the mercury to top out at 37 and bottom at 27.
What comes next
This is the outlook from the officials:
– Some more poor AQI in the offing
– Things should pick up once the dust is gone
– Expect wind on Monday afternoons
– No GRAP Stage-I in the cards
In a word, the dust has put Delhi in the ‘poor’ zone at the height of the sultry season. The CAQM is banking on some let-up when the plume from across the border dies down, but for now, the city has to make do with gritty air and hot evenings.
