Mercury dips to single digit for the first time this season in Delhi, leads to ‘poor’ air

The city’s temperature dipped to a single digit for the first time this season, with the minimum temperature plummeting to 9.4 degree Celsius on Sunday. The dip in temperature as well as the low wind speed contributed to the deterioration of the air quality of the city into the ‘poor’ category.

On Sunday, the maximum temperature was recorded at 22.8 degrees Celsius, three degrees below normal. The minimum temperature reached 9.4 degrees Celsius, which was a notch below the season’s normal. Between 5am and 7am, there was dense fog, which caused visibility at the Palam and Safdarjung observatories to fall to zero metres.

The overall Air Quality Index (AQI) reading of Delhi was also recorded at 250, in the ‘poor’ category, according to the Central Pollution Control Board (CPCB). At 8pm on Sunday, the air quality at Dwarka, Nehru Nagar, Jahangirpuri, Rohini, Wazirpur and Mundka monitoring stations had already reached the ‘very poor’ category. The AQI reading on Saturday was 193—in the ‘moderate’ category.

Scientists at the India Meteorological Department (IMD) said that the wind speed on Sunday hovered between 8-10kmph, which was not enough to disperse the pollutants. The dip in temperature also contributed to the worsening air quality.

“In the morning, the temperature dipped and the wind speed was not strong enough—these were the primary reasons behind the dip in air quality,” Kuldeep Srivastava, head of IMD’s regional weather forecasting centre, said.

Srivastava warned that in the coming days the AQI reading is expected to deteriorate further. On December 4, the forecast states that the minimum temperature is likely to reach nearly 8 degrees Celsius and the wind speed will also remain in the 4-6kmph range. As temperature falls, the air becomes colder and more dense and this traps the pollution particles closer to the ground, leading to deterioration of air quality.

On Saturday, Delhi witnessed its first episode of dense fog, and after a day of breathing ‘satisfactory’ air on Friday the AQI levels reached ‘moderate’.

The Centre has asked all Metro rail corporations to install retrofitted devices in diesel generator (DG) sets being used by them, a move aimed at reducing particulate matter emissions from DG sets.

In a letter to the corporations, the union housing and urban affairs (HUA) ministry said that according to National Clean Air Programme (NCAP), DG sets contribute 7-18% to the ambient air pollution in non-attainment cities.

Non-attainment cities are areas with air quality worse than the National Ambient Air Quality (NAAQ) Standards.

There are several Metro rail corporations, including Delhi Metro, Chennai Metro and Bengaluru Metro.

The ministry said DG sets are used on a large scale in Metro line construction, emergency power supply in Metro rail, places with tourist infrastructure, central command rooms, wastewater treatment plants, construction and infrastructure works.

It also asked Metro rail corporations to use retrofitted emission control equipment with diesel generators having a minimum specified particulate matter capturing efficiency of at least 70%.

The government has also asked Metro rail corporations to shift to gas-based generators either by retrofitting existing generators for partial usage of gas (a mixture of diesel and gas) or buying new gas-based generators.

In a recent communication to ministry, Centre of Excellence for Research on Clean Air, IIT Delhi also mentioned there is a huge scope to reduce the adverse impact of pollution through installation of retrofitted emission control system in DG sets.

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