City’s air quality enters severe category for the second time this week

Air quality in the city entered the “severe” category on Saturday for the second time this season with a reading of 439 on the Central Pollution Control Board’s

Air quality in the city entered the “severe” category on Saturday for the second time this season with a reading of 439 on the Central Pollution Control Board’s (CPCB) air quality index (AQI) bulletin. Saturday’s reading is up from the previous day’s AQI reading of 392 in the “very poor” category. Earlier, on Thursday, the air quality had entered the “severe” category.

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Officials and experts attributed the spike in pollution to low wind speed, falling temperature and stubble burning. According to the early air quality warning system for Delhi-NCR, the air quality is likely to remain in the upper end of the “very poor” category on Sunday. Air quality is expected to remain in the “severe” to “very poor” categories on Monday as well. The average daily concentration of particulate matter (PM) 2.5, the city’s most prominent pollutant, on Saturday was 436.95µg/m³, as per the HSPCB’s official air quality monitor at Vikas Sadan.

“Low speed winds are a major reason behind the increase in pollution. Due to calmer wind speed, the dispersion of pollutants is not taking place adequately. In the morning hours, particularly between 4am and 7am, there is a peak in the level of pollutants due to thermal inversion. The mixing height is also coming down; it is roughly 40% less than what it used to be earlier. As a result, accumulation of pollutants is higher,” said Sachin Panwar, a city-based air quality scientist.

The mixing height is the vertical height at which suspended particles mix with the air. Due to a dip in temperatures, the air rising from the surface cannot reach a particular height for dispersal. Panwar said that while some relief could be expected on Sunday and Monday, more peaks could be expected next week between November 10-12.

Kuldeep Srivastava, a scientist at Indian Meteorological Department (IMD) and the head of Regional Weather Forecasting Centre, also reiterated that pollution had increased due to poor dispersal of pollutants. “The pollutants have accumulated since dispersal is poor due to low wind speed. We can expect some improvement if wind speed picks up,” said Srivastava.

On Saturday, the city recorded a minimum temperature of 13 degrees Celsius, three degrees below the normal. The maximum temperature was recorded at 29.9 degrees Celsius. The minimum temperature is expected to hover around 13 degrees Celsius on Sunday while the maximum temperature is expected to be around 30 degrees Celsius. Clear skies are expected to prevail this week, as per the IMD’s weekly forecast.