SC panel to track cyclones in Bay of Bengal to predict pollution in Delhi-NCR
Tropical cyclones that originate in the Bay of Bengal have an indirect bearing on air quality in Delhi, said D Saha,head of the air quality laboratory of Central Pollution Control Board.delhi Updated: Oct 28, 2017 16:07 IST
The Supreme Court-empowered Environment Pollution Control Authority (EPCA) will now monitor tropical cyclones developing over Bay of Bengal to understand and predict pollution patterns in Delhi.
Air quality in Delhi starts deteriorating from October as winter approaches, the time when these atmospheric conditions start developing. It has already hit the very poor levels. Usually it toggles between moderate and poor levels throughout the year.
Tropical cyclones that originate in the Bay of Bengal have an indirect bearing on air quality in Delhi, said D Saha,head of the air quality laboratory of Central Pollution Control Board.
“Moisture laden easterly winds, triggered by these weather systems, not just spike pollution levels in Delhi–NCR but also create smog during this time of the year,” said Saha.
The EPCA has sought help from India Meteorological Department (IMD) in this regard, confirmed panel member Sunita Narain. “We have asked the IMD to give us updates whenever such systems build up in the sea. Tropical cyclones and other bad weather conditions over the sea have a vital role in deciding air quality of Delhi,” said Narain.
India witnesses the maximum number of cyclones in October and November, shows data available with the IMD since 1891. This is also the time when pollution levels shoot up in Delhi-NCR to very poor and severe levels because of multiple other sources such as stubble burning and bursting of fire crackers among others.
However, scientists have also established a direct link between the weather conditions triggered by these cyclones and the poor air quality in Delhi. Moist air helps the gaseous pollutants to condense and form particulate matter. The air becomes heavy and dense. Moist air has greater holding capacity and pollutants linger in the air for much longer period. They get trapped, explained Saha.
The case in point is the spike in post-Diwali pollution.
Despite a decline in the amount of firecrackers burst and the smog, the air quality in Delhi dropped to severe level, a day after Diwali. However it cleared out within three days after wind patterns became favourable with the blowing of strong north westerly winds.
However, in 2016, the weather conditions were more favourable to pollutants. The air was denser, leading to the worst smog in Delhi-NCR in 17 years. The pollution took 26 days to return to pre-Diwali levels.
“This year a depression over the Bay of Bengal had triggered heavy rains in West Bengal and Odisha around Diwali. The system also triggered easterly winds which brought in lots of moisture in Delhi – NCR. This helped to spike the pollution levels a day after the Diwali,” said a senior official of the Met department.
Atmospheric depression and cyclones which form in eastern India and Bay of Bengal block the passage of the north westerly winds. With the cross ventilation being stopped the wind speed drops and the pollutants are deposited on the way.
In the last 15 years IMD had recorded at least 41 tropical cyclones and depressions during this time of the year. Bay of Bengal witnesses more cyclones than the Arabian Sea.