In four years, second most polluted December in Delhi
Scientists said conditions over the past few weeks have been in complete contrast to the favourable meteorological conditions that cleaned up Delhi’s air last month making it the cleanest November since 2015.Updated: Dec 26, 2018 10:22 IST
Unfavourable weather conditions pushed pollution levels up to such extremes over Sunday and Monday that Delhi recorded the second most polluted December day in four years.
Scientists said conditions over the past few weeks have been in complete contrast to the favourable meteorological conditions that cleaned up Delhi’s air last month making it the cleanest November since 2015.
This is the second most polluted December day since 2015 when the National Air Quality Index was introduced. In 2017, the AQI had shot up to 469 making it the most polluted December day so far. While the AQI was recorded to be 450 on Sunday, it dropped to 448 on Monday.
“In 2016 — the year in which Delhi encountered its worst pollution — there were at least six days in which air quality was in the severe zone. But pollution was not so high. The highest AQI recorded in December 2016 was 427,” said an official of the Central Pollution Control Board (CPCB).
The concentration of particulate matter in Delhi’s air hit the emergency levels since late evening and night of Saturday. Situations turned particularly bad on Sunday evening when in some areas like as Anand Vihar, Wazirpur and Ashok Vihar, the hourly levels of PM10 and PM2.5 shot up to more than 15 times over the daily permissible limits.
Authorities blamed the worsening pollution on the unfavourable meteorological conditions and said conditions are unlikely to improve before December 26. On November 4, the AQI had improved to 171 (moderate zone) – the cleanest in November since 2015.
“The three main triggers which pushed up pollution levels were low wind speed, high relative humidity levels and fall in temperature. The mixing height (room available for vertical dispersion of pollutants) and the ventilation index (factor which determines how fast pollutants can disperse) have also gone down,” said a senior official of the Delhi Pollution Control Committee (DPCC).
While Delhi needs a minimum wind speed of 10 km/hour to disperse locally emitted pollutants, the wind speed has dropped below 5 km/hour. The ventilation index, which should have been more than 6,000sqm/sec, had dropped to around 1,000sqm/sec on Sunday. On Monday it was around 4,000sqm/sec.
“Such high levels of pollution are rarely encountered in December. They are usually seen in November when the monsoon has just retreated and winter is yet to set in, while Diwali is round the corner and stubble burning is going on. Meteorology has played a very crucial role in pushing up pollution levels,” said D Saha, former head of the air quality laboratory of CPCB.
Authorities have banned construction and industrial activities in Delhi and NCR cities till Wednesday, as the air quality continued to reel under ‘emergency’ levels – the highest category of pollution. In such conditions, the air is severely harmful even to healthy citizens.
Situations worsened to such extent over the past 48 hours that the Union environment secretary had to hold ‘rounds of discussions’ with the Delhi chief secretary to insist that localised actions be implemented in full swing.
The multi-agency task force headed by CPCB held an emergency meeting and recommended a two-day ban on construction and industrial activities, which were forthwith implemented by the Supreme Court appointed body Environment Pollution (Prevention and Control) Authority. The task force had met on Saturday and had advised people with respiratory ailments to stay indoors.
“While on one hand construction activities have been banned across Delhi and in four NCR cities (Faridabad, Ghaziabad, Noida and Gurgram), industrial activities have been banned in at least six industrial areas in the NCR, including four in Delhi – Narela, Bawana, Mundka and Wazirpur,” officials said.
Traffic police have been asked to deploy special teams to ensure free flow of traffic and that all non-destined heavy vehicles are diverted through the peripheral expressways.