Rain, strong winds improve Delhi's air quality to 'moderate' category

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New Delhi, Jan 4 (PTI) Delhi's air quality improved significantly to the 'moderate' category on Monday owing to rain and strong winds.

A government forecasting agency said the air quality is likely to improve further to the 'satisfactory' category.

The city's 24-hour average air quality index (AQI) was 151 on Monday. It was 354 on Sunday and 443 on Saturday.

An AQI between zero and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'.

Officials at the India Meteorological Department said rain and winds gusting up to 30 kmph under the influence of a strong Western Disturbance dispersed pollutants.

The Safdarjung Observatory, which provides representative data for the city, recorded 1.4 mm rainfall on Monday. It had gauged 39.9 mm rainfall between 8:30 am on Saturday to 2:30 pm on Sunday. More rain is likely on Tuesday. The maximum wind speed will be around 30 kmph, the IMD said.

The central government's Air Quality Early Warning System for Delhi said the AQI is likely to remain in the 'moderate' to 'satisfactory' on Tuesday.

It said the city's ventilation index -- a product of mixing depth and average wind speed – would be 5,000 m2/s on Monday and Tuesday.

Mixing depth is the vertical height in which pollutants are suspended in the air. It reduces on cold days with calm wind speed.

A ventilation index lower than 6,000 sqm/second, with the average wind speed less than 10 kmph, is unfavourable for dispersal of pollutants. PTI GVS TDS TDS