Air quality severe, but rain may bring some respite

New Delhi: The air in Delhi turned foul on Wednesday, with the air quality index (AQI) plunging to severe level owing to a layer of cloud and pollutants that stopped the sunlight from reaching the ground. To make matters worse, calm winds bearing high moisture could not disperse pollutants.

Air quality severe, but Rain may bring some respite

Air quality severe, but rain may bring some respite
         

New Delhi: The air in Delhi turned foul on Wednesday, with the air quality index (AQI) plunging to severe level owing to a layer of cloud and pollutants that stopped the sunlight from reaching the ground. To make matters worse, calm winds bearing high moisture could not disperse pollutants.

However, a respite is in sight, says the weatherman— Light rain, strong surface winds and thunderstorm are predicted over the next two days, and they, hopefully, will clear the air.

According to Central Pollution Control Board (CPCB)’s 4pm bulletin, the AQI, on a scale of 0 to 500, was 408 or ‘severe (401-500)’ in Delhi. It was in the ‘very poor (301-400)’ category for the past five days. On December 6, the AQI was ‘severe’ at 404.

The levels of PM 2.5 — the fine particulate matter or the most harmful aerosol in Delhi air — was recorded as 262?g/m3 at 7pm, near the emergency mark of 300?g/m3, and four times the national limit of 60?g/m3. The PM 2.5 levels started spiking from Tuesday evening.

The levels of PM10 (coarse particles), at 415?g/m3 (7pm), was also near the emergency mark of 500?g/m3, and four times the safe limit of 100?g/m3.

India Meteorological Department (IMD) scientists said the reason the air quality deteriorated was because the wind speed fell to nearly zero on Tuesday night and early Wednesday. Moisture levels also increased as the winds changed to easterlies, which makes pollution particles heavy and more concentrated near the surface.

“Moisture has increased; wind direction has also changed to easterly because of a developing western disturbance. The contribution from fire or dust is negligible as per our models. There are some crop fires in Uttar Pradesh but I don’t think these are contributing to pollution in Delhi. We are expecting air quality to clear once it rains in the next couple of days,” VK Soni, senior IMD scientist in-charge of air quality early warning system, said.

The average wind speed during the afternoon was 8-10 kmph, which is not favourable for dispersion of pollutants.

“Thunderstorm and rainfall with surface winds picking up pace to 20-30kmph is expected to clear the air. This will be a cumulative impact of rainfall, hailstorm and snowfall predicted in the Western Himalayan region, for which a warning has been issued in those states,” Kuldeep Shrivastava, IMD’s head of regional weather forecasting centre, said.

According to IMD’s bulletin Wednesday, the minimum temperature was 7.9 degrees Celsius, a notch below the season’s average. However, it was higher than Tuesday’s 7.4 degrees Celsius — the coldest of the season so far. The minimum temperature will, however, go up temporarily till December 14 because of clouding associated with western disturbance. But the maximum will dip to around 20 degrees Celsius, mainly because of the rain.

However, the respite may be short-lived, as ‘dense’ fog and an expected dip in mercury on December 15-16, may push up pollution levels again.

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