Air quality deteriorates to settle in poor zone as winds slow down

The average air quality index (AQI) as per the Central Pollution Control Board (CPCB) at 4pm was 225, which falls in the ‘poor’ zone, as against 100 in the ‘satisfactory’ category, the previous day.

After two days of relatively good air, the air quality in the national capital plunged back into the ‘poor’ zone on Sunday. While rainfall and strong winds had kept the air quality in check over the past two days, it deteriorated as winds slowed down leading to slower dispersal of pollutants hanging in the air, said government agencies.

On a scale of 0 – 500, an AQI value between 0-50 is considered ‘Good’ and a value between 50 and 100 is considered to be ‘Satisfactory’. (Sushil Kumar/HT PHOTO)

The average air quality index (AQI) as per the Central Pollution Control Board (CPCB) at 4pm was 225, which falls in the ‘poor’ zone, as against 100 in the ‘satisfactory’ category, the previous day. On Friday, when light rainfall and gusty winds swept the city, the AQI was 144, which is in the ‘moderate’ zone.

On a scale of 0 – 500, an AQI value between 0-50 is considered ‘Good’ and a value between 50 and 100 is considered to be ‘Satisfactory’.

According to CPCB officials, the air quality is likely to remain ‘poor’ and may deteriorate further over the next two days. “The winds are going to remain slow and the ventilation index is likely to remain low on February 24-25, both of which do not allow dispersion of pollutants,” said a senior official.

According to scientists at the India Meteorological Department (IMD), the light rain and strong winds on Friday up to a speed of 30-35kmph had cleared the air of the accumulated pollutants. However, the wind speed on Sunday fell to around 4 kmph, which is not favourable for dispersal of pollutants.

“The humidity is also slightly high. Both these factors allow for lesser ventilation and hence higher pollution levels. The wind speed is likely to remain around 4-6 kmph over the next two days,” said a senior IMD scientist.

As per a bulletin by the System of Air Quality and Weather Forecasting and Research (Safar), a unit of the union ministry of earth sciences, the overall air quality in Delhi is expected to deteriorate till February 25.

“SAFAR model suggests AQI deteriorates to the lower end of the poor category by tomorrow. A slight increase in wind speed is forecast for February 25. AQI is likely to be in the poor category,” it said.

Air quality in Delhi usually hovers in the ‘moderate’ and ‘poor’ categories during the summer. According to IMD scientists, winter is almost over in Delhi while mercury is set to rise from Monday onwards.

On Sunday, the maximum temperature was recorded as 26.8 degrees Celsius, two notches above normal. The minimum settled at 12.8 degrees Celsius, also two notches above the season’s average.

“Both day and night temperatures are likely to rise by a degree or two from Monday onwards,” the scientist said.