December 8, 2021 2:14:07 am
Recent meteorological conditions have brought with them an improvement in air quality in Delhi.
The city’s 24-hour average AQI stood at 255 on Tuesday, in the ‘poor’ category, according to the Central Pollution Control Board (CPCB). On Tuesday, the AQI had improved as opposed to a figure of 322 on Monday, and 305 on Sunday.
The light rainfall that parts of the city witnessed on Sunday helped wash away some of the accumulated pollutants, and thereafter, the temperature has not declined enough for pollutants to accumulate again, said Gufran Beig, founder project director, SAFAR. Wind speed had also improved from Monday night, and the improved wind speed will persist for the next three days at least, Beig said.
In winter, air close to the surface cools down with a fall in temperature and becomes denser, making it difficult for this layer to mix with the warmer air above it, thereby trapping pollutants closer to the surface of earth.
Usually, during this time of the year, the boundary layer is at a height of less than 1 km, and a low boundary layer traps pollutants close to the surface, Beig said. “Now, the boundary layer is around 1 to 1.5 km, which means that vertical mixing is also high,” he said. Vertical mixing allows pollutants to disperse upwards.
The boundary layer is higher because the atmosphere is relatively cleaner due to wind speed, and the temperature has not dropped as much as it could have, Beig said, explaining that the temperature is only dropping slowly. “The wind speed keeps the horizontal mixing high,” he said. These factors also mean that the air quality over the next four days is likely to “improve gradually but within the ‘poor’ category,” according to the SAFAR forecast.
The India Meteorological Department (IMD) has predicted a gradual fall in minimum temperature by around 2 to 4 degree Celsius over most parts of northwest, central and east India during the next four to five days.
The AQI at some monitoring stations, which had remained in the ‘severe’ category on December 4, had recorded improvements by Tuesday. At Anand Vihar, for instance, the AQI as a 24-hour average at 8 pm was 269, while the average was 419 on December 4. At Jahangirpuri, the average AQI was 302 on Tuesday, down from 425 on December 4.
Meanwhile, the Commission for Air Quality Management (CAQM) has ordered the immediate closure of industries where PNG infrastructure and supply are available, but units have not yet switched to PNG. These industrial units will not be allowed to function till December 12.
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