Why is Delhi air cleaner? Count of farm fires is not the only factor
The AQI in Delhi fell 243 factors between Friday and Sunday, and from extreme to poor in lower than 24 hours. (File)

Friday, November 15: A thick layer of haze engulfs Delhi, the scent of smoke in the air discernible. Air Quality Index: 458 (extreme)

Saturday, November 16: Air high quality improves to “very poor” however the layer of haze stays thick. AQI: 357 (very poor)

Sunday, November 17: Clear skies, shiny sunshine and powerful winds. AQI: 216 (poor)

Looking for causes

The AQI in Delhi fell 243 factors between Friday and Sunday, and from extreme to poor in lower than 24 hours. Social media buzzed with photographs of a transparent sky and a shiny day, which had eluded Delhi for at the very least per week.

Delhi Chief Minister Arvind Kejriwal, who had put the blame for the poisonous air on Punjab and Haryana for failing to manage crop stubble burning, posted {a photograph} of the clear skies on Sunday and tweeted, “We live in such a beautiful city. Imagine, if the stubble burning were to stop, our skies will look like this all year round and our health will also improve.”

Was it only a dip in the quantity of farm fires that helped clear Delhi’s air inside hours? Experts say it takes much more than that to clarify Delhi’s air high quality.

Wind course & velocity

According to officers at the Central Pollution Control Board, a change in wind course and a sudden enhance in wind velocity had been the major causes behind Delhi going from extreme to poor in just a little over a day. Wing blowing northwest brings air pollution from Punjab and Haryana to Delhi; on Friday and Saturday, the course modified to northerly.

“On Friday, the average wind speed in Delhi was under 10 km/hr. Because of an active western disturbance, the wind speed gradually rose and on Saturday it was around 12 km/hr. By late Saturday night, an even bigger increase in wind speed was seen and within hours, the air quality improved,” mentioned a senior IMD official. On Sunday, the wind velocity was round 35 km/hr. “At this speed, pollutants 250 km away can reach a spot within 8 hours and also be flushed out as quickly if the wind speed holds.”

Geographic location

Air high quality deteriorates or improves for a range of causes, the major being emissions. In Delhi, vehicular emissions, highway and building mud, waste burning and industrial air pollution play key roles. Add to this Delhi’s location — on the Indo-Gangetic Plain (IGP), the most polluted belt in the nation.

“Pollution is not Delhi’s problem alone. If we plot the most polluted cities in India on a map, most will fall on the IGP. This is because of the predominant wind direction and the way dust travels. On Sunday, for example, when Delhi’s air quality improved significantly because of strong winds, Kolkata’s AQI went from moderate to poor,” mentioned Dipankar Saha, former air laboratory head at CPCB.

An official at IMD Chandigarh mentioned: “Delhi gets polluted due to its own base pollution levels. With the onset of winter, the air’s carrying capacity for pollutants increases,and if winds are slow, it does not disperse, effectively trapping pollution in Delhi.”

Stubble burning

A take a look at the contribution of stubble burning to Delhi’s air, calculated by SAFAR exhibits that farm fires’ contribution to PM2.5 ranges was lower than 150 micrograms per cubic metre for almost a month, together with on severely polluted days.

On November 12, when PM2.5 focus was almost 400 µg/cu. m, stubble burning contributed round 100 µg/cu. m. But on November 15, when PM2.5 once more touched 400, farm fires’ share fell to round 50 (Figure 1). Days with the most farm fires had been not the days with the highest air pollution. On November 5, Punjab and Haryana noticed greater than 6,000 fires, however Delhi’s AQI was in the very poor vary with the stubble burning contributing 12% to PM2.5.

“To say that farm fires in Punjab do not affect air quality in Delhi is wrong but to say that only farm fires spoil Delhi’s air is equally wrong,” a CPCB official mentioned.

What to count on

Fire maps primarily based on NASA satellite tv for pc photos present a rise in the quantity of energetic fires between November 14 — when Delhi noticed the worst air high quality of the season to date with an AQI of 463 — and November 18. This is unhealthy information for Delhi, with wind anticipated to decelerate and blow from the northwest and west.

According a supply in the Punjab Agriculture Department, the crop-stubble burning season is at its fag finish. Agriculture Secretary K S Pannu mentioned the state expects farm hearth incidents to cease utterly by the finish of the week.

On Monday, 500 fires had been recorded, however on Tuesday, this quantity rose to 1,289. According to forecasts, Delhi’s air is anticipated to deteriorate to very poor on Wednesday and extreme on Thursday.

Inputs by Shivam Patel in New Delhi

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