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Pollution levels dip slightly as winds over Delhi pick up pace

CPCB data showed that the overall air quality index (AQI) on Thursday was 199, in the ‘moderate’ category and a marginal improvement from Wednesday’s 221.
While this was higher than Wednesday’s 12%, the pollution levels were lower because of the relatively higher local wind speeds. (Parveen Kumar/HT Photo)
Published on Oct 22, 2021 06:10 AM IST
ByJayashree Nandi, Hindustan Times, New Delhi

Delhi’s air quality improved slightly as winds picked up on Thursday, Central Pollution Control Board (CPCB) recordings showed, and scientists separately predicted that emissions from farm fires in Punjab and Haryana are unlikely to pose a threat immediately.

CPCB data showed that the overall air quality index (AQI) on Thursday was 199, in the ‘moderate’ category and a marginal improvement from Wednesday’s 221.

Union ministry of earth science’ air quality monitoring centre’s System of Air Quality and Weather Forecasting And Research (Safar) showed that 1,234 farm fires were seen in the neighbouring states of Punjab and Haryana through satellites on Thursday, which contributed to nearly 15% of the city’s PM 2.5 (particulate matter with diameter less than 2.5 micrometres) levels.

While this was higher than Wednesday’s 12%, the pollution levels were lower because of the relatively higher local wind speeds.

“Local winds are moderate that enhances dispersion of pollutants keeping AQI in moderate category. Share of fire emissions is expected to increase in next two days. In presence of local dry weather and north-westerly wind local dust emission leads to increase of PM10 (particulate matter with diameter less than 10 micrometres). The overall AQI is likely to degrade to poor in next two days,” the Safar air quality analysis read.

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Senior scientists from the India Meteorological Department (IMD) said that under the impact of a western disturbance, there is a possibility of cloudy skies coupled with isolated rain in some areas between October 23 and October 24. The western disturbance will also be marked by a slight increase in the temperatures in Delhi on October 22.

On Thursday, the maximum temperature at the Safdarjung weather station, which provides representational data for the entire city, was 32.4 degrees Celsius. The minimum was 16 degrees Celsius, two degrees below what is considered normal for this time of the year. The maximum temperature at the Palam observatory was 32 degrees Celsius, a notch below normal, while the minimum temperature here was recorded 18.3 degrees Celsius.

“The air quality is likely to remain in the poor category in the next few days. As for the temperatures, there will be a slight rise on account of the passing of the western disturbance. Temperatures might start falling by the end of October,” said a senior IMD official.

For the next five days, local pollution sources such as vehicular emissions, construction dust, residential emissions and pollution from industries within and in the peripheries of the city are likely to be the primary reasons for bad air, a forecast by the Indian Institute of Tropical Meteorology’s decision support system showed on Thursday.

IITM’s decision support system, which is an early warning system that forecasts the primary pollution sources that contribute to the Capital’s air pollution at any given time of the day, showed on Wednesday that vehicular emissions are likely to be the highest contributor in the city’s pollution levels in the next five days. The share in Delhi’s PM 2.5 (particulate matter with a diameter less than 2.5 micrometres) is forecasted to range between 10-35% in the coming days.

The DSS forecast said that on October 22, the contribution of vehicular emissions is expected to reach around 22%, and it will continue to rise and 30.35% on October 23 and then 32.66% on October 25.

Apart from vehicular emissions, other local sources that are also expected to act up in the coming days are industries in Delhi and its peripheries (4-6%), pollution from residential sources (3-9%), construction (3-5%), waste burning (2-3%), power plants (1-2%) and road dust (1-2%).

“The predominant surface wind was from northwest directions of Delhi with a wind speed of around 10-16 kmph and mainly clear sky on October 21. This will change to west/southwest with speed of 08-20 kmph and mainly clear sky October 22,” the DDS forecast read.

Weather forecasters and scientists at the India Meteorological Department (IMD) said that there may be a fall in the contribution of stubble fires to Delhi’s pollution, possibly because of moderate to heavy showers predicted in parts of Punjab and Haryana on between October 23 and October 24.

“Under the impact of a western disturbance, there is a forecast of moderate to heavy rainfall in parts of Punjab and Haryana on October 23-24. In Delhi this would probably only cause isolated showers,” said Mahesh Palawat, vice-president (meteorology and climate change), Skymet Weather Services.

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