An interplay of meteorological factors—all turning unfavourable over the last 48 hours—is largely behind the sharp deterioration in Delhi’s air quality expert said.
To begin with, Delhi’s minimum temperature was down to 15.6 degrees Celsius on Sunday – the lowest so far this season. Low temperatures slow down dispersion of pollutants and also lead to calm winds at night, another factor that led to spike in pollution on Sunday.
Kuldeep Srivastava, scientist at India Meteorological Department (IMD) said wind speeds remained calm in the early hours of the day and were below 5 km/hour till around 2:30pm. “We saw haze throughout the day and visibility was down to around 1,500-1,800 metres during the day. Normally, it is over 4,000 metres,” said Srivastava, adding that the wind direction was also predominantly northwesterly, which transported stubble pollutants from Punjab and Haryana to the capital.
Delhi sees a transition to northwesterly winds from the first week of October, when the southwest monsoon departs. These winds begin to influence Delhi’s air quality negatively as farm fires spike in Punjab and Haryana – carrying particulate pollutants to Delhi, experts said.
Srivastava said low temperatures, in addition to predominantly northwesterly winds will continue to influence air quality till February. As temperatures dip further, so will the mixing height — an invisible layer in the atmosphere within which particulate matter gets trapped. The lower the mixing height, the poorer air quality as pollutants are closer to the surface and unable to disperse.
On Sunday, while the air quality in most of the 40 air quality monitoring stations was recorded in the very poor range, some logged readings closer to 400 (severe category).
Central Pollution Control Board (CPCB) data showed that Nehru Nagar near Lajpat Nagar recorded the highest average AQI of 384 (very poor). This was followed by New Moti Bagh (377) and Shadipur (372) — all stations located near roads carrying heavy traffic.
Pusa in west Delhi, with an average AQI of 209 (poor) was comparatively the cleanest, followed by DTU in north Delhi (219).
Data for four air quality monitoring stations was unavailable on Sunday, which included Anand Vihar, a pollution hotspot. Experts said the large gap in Delhi’s most polluted and least polluted locations, shows the impact of local sources of air pollution becomes particularly prominent on days with a high AQI.
“While this indicates the role of the location of the station too, such a high difference also indicates that local sources and in this case, vehicles are playing a key role. The locations recording a higher reading than the average are locations where daily localized action can be undertaken and small measures like decongesting roads, or sprinkling water to control dust are actions easily possible,” he said.
Source: Hindustan Times
