Delhi gets satisfactory air after three months

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Delhi residents on Sunday were greeted with the cleanest air they have breathed in months after strong winds and moderate rain helped disperse pollutants, as the air quality touched “satisfactory” levels after 91 days.

The 24-hour average Air Quality Index (AQI) reading, as calculated by the Central Pollution Control Board (CPCB)’s 4pm bulletin, was 90 on Sunday, placing it in the “satisfactory” zone. This was an improvement from Saturday’s 135 (moderate).

Scientists credited the improvement in air quality to a western disturbance. “The improvement in air quality is due to a western disturbance that had started in northern India on February 28 and moderate rainfall experienced in Delhi NCR, Haryana, and Punjab,” said Kuldeep Srivastava, head of the India Meteorological Department (IMD)’s Regional Weather Forecasting Centre.

Western disturbance refers to moisture-heavy winds that blow in from over the Arabian Sea and parts of west Asia, which then precipitate as rain over the plains and as snow in the mountains in winter months.

Srivastava added that apart from the rain, strong winds of 30-35 km per hour through Saturday also ensured that pollutants in the air were dispersed, consequently improving the air quality. CPCB data appeared to confirm this.

Particulate matter dropped to safe limits in the Capital as the winds picked up by Saturday evening.

PM10 (particulate matter with diameter less than 10 micrometres) levels in Delhi, which were 243.3µg/m3 on February 26 at 11pm, dropped to 62.4 µg/m3 by 7pm on Sunday. The daily safe limit for PM10 is 100µg/m3. Similarly, PM2.5 (particulate matter with diameter less than 2.5 micrometres) levels started dropping from 129.1µg/m3 at 11pm on February 26 to 31.8µg/m3 on Sunday at 7pm, according to CPCB data. The daily safe limit for PM2.5 is 60µg/m3.

IMD said the Safdarjung Observatory recorded 18.6 mm rainfall till 8.30am on Sunday while the weather stations at Palam and Lodhi Road gauged 15.4 mm and 19mm precipitation respectively.

The minimum temperature was recorded at 14.4 degrees Celsius — two degrees above normal for this time of the season. The IMD has forecast mainly clear sky and shallow fog in the morning on Monday. The maximum and minimum temperatures are likely to settle around 28 and 13 degrees Celsius.

However, experts warned that the relief will is likely to be short-lived. The air quality is expected to deteriorate in the next few days in the absence of rainfall and a drop in wind speed, they said.

“The air quality was in ‘poor’ category all this while and it improved significantly today because of the rain. But from tomorrow (Monday) the temperature is likely to go down and wind will be slower. In view of this, the dispersions are expected to be less and local emissions will start getting accumulated, bringing the air quality to ‘moderate’ level by tomorrow and to ‘poor’ category the following day,” said an official from the System of Air Quality and Weather Forecasting and Research (SAFAR).

The air, however, is expected to improve from the evening of March 4 again as an active western disturbance is likely to affect north India during March 4 to 6 when rain and thunderstorm accompanied with hailstorm will occur over western Himalayan regions as well as plains of north west India.

Under the influence of the western disturbance, rain accompanied by gusty wind and hailstorm is expected to occur over Delhi-NCR between the evening of March 5 and March 6, Srivastava said.