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Weekend to get colder, air quality worsens

By HT Correspondent
PUBLISHED ON DEC 26, 2019 08:35 PM IST

Gurugram Thursday was yet another ‘severe cold’ day in the city as the maximum temperature was 11.8 degrees Celsius, nine degrees Celsius below the normal for this time of the year, as per the India Meteorological Department (IMD). Wednesday’s maximum temperature was 11.2 degrees Celsius, the season’s lowest so far.

The minimum temperature was also below the normal by two degrees Celsius, at 5.4 degrees Celsius. It fell marginally from 5.7 degrees Celsius the previous day, as per the IMD data.

Air quality in the city remained in the ‘poor’ category of the Central Pollution Control Board’s daily air quality index (AQI) bulletin, deteriorating to an index value of 290 on Thursday, from the previous day’s reading of 211. The average daily concentration of finer particulate matter on Thursday was 249ug/m3, as per the city’s official air quality monitor at Vikas Sadan, up from the previous day’s 203ug/m3.

The minimum temperature on Saturday is expected to fall further to around 4 degrees Celsius, as per the IMD’s prediction. The maximum temperature on Friday and Saturday could be around 12 degrees Celsius, the MeT department said.

“With the minimum temperature dropping to 4 degrees Celsius on Saturday and Sunday, cold wave conditions are expected in NCR,” said Kuldeep Srivastava, a senior scientist at the IMD.

Experts and officials attributed the uptick to prevailing cold day conditions and reduced wind speeds. “Wind speed on Thursday was between 6 and 10 kmph, which is not ideal for dispersal of pollutants. The ventilation index over NCR on Thursday was about 4,500m2/s, whereas one needs a ventilation index of at least 6,000m2/s to effectively clean up the air,” a senior scientist at the CPCB’s air quality lab in Delhi said.

With wind expected to slow down further over the weekend, air quality stands to deteriorate. The predicted ventilation index over Delhi-NCR on Friday is 2,000m2/s, and 1,000m2/s on Saturday. Moreover, the ‘mixing depth’ of pollutants (which refers to the height at which they settle above the earth’s surface) was just 900 metres on Friday, and is expected to drop to 800 metres on Saturday.

According to the early air quality warning system for Delhi-NCR, “Air quality is likely to remain in ‘very poor’ category on December 27. The air quality will start deteriorating on December 28 and reach the upper end of ‘very poor’ category owing to low wind speed and poor ventilation index. The air quality is likely to reach the ‘severe’ category on December 29.”

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