‘Moderate’ AQI in Chennai on Bhogi day – The Hindu

The Air Quality Index (AQI) declined on Bhogi day across the city even as a thick layer of smoke covered many places on Saturday.

The India Meteorological Department said the visibility had dropped to 600 metres during early morning hours of Saturday. There was no fog condition reported over the city.

Officials of the Aerodrome Meteorological Office, Meenambakkam, noted the visibility steadily dipped from 5.30 a.m. and it improved to 1,500 metres only around 9.30 a.m. This year, calm wind prevailed since 10 p.m. on Friday leading to smoke suspension in the air and low visibility for three hours on Saturday after 5.30 a.m. Visibility was around 1,500 metre around 4.30 a.m. due to variable wind.

Wind speed too was at its lowest of 4 kmph and the smoke dispersed only after 10 a.m. on Saturday when strong easterlies started blowing with a speed of 10km per hour, said V.R.Durai, Scientist-F, Aerodrome Meteorological Office. Normally, the visibility level is around 3,000 metres at 10 a.m. But, on Saturday, it had improved to only 2,000 metres by 10 a.m., he said.

However, the low visibility level did not affect flight operations on Saturday. A minimum visibility of 550 metre is needed for flight operations and flights would be diverted if it dipped below 350 metre.

Last year, the visibility level improved to 1,000 metre around 8 a.m. due to presence of strong wind. In 2020, visibility dipped to lowest of 150 metre at 7.15 a.m. due to smoke.

On Saturday, data from the SAMEER app, which provides hourly updates published by the Central Pollution Control Board showed moderate AQI (in the range of 100 to 200) in almost all the eight monitoring stations.

The index inched up a few points every one hour from morning to noon, pointing to a steady decline in air quality. The AQI at Alandur air quality monitoring station declined from 165 at 8.10 a.m. to 197 at 12.10 p.m., close to ‘poor’ category.

Health impacts of moderate air quality include breathing discomfort to people with asthma and other respiratory diseases, as per the CPCB.