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Rainwater over Pune region alkaline in nature: IITM study

A team of researchers collected rainwater samples from Pashan (urban) and Sinhagad (rural) during monsoon from 2006 to 2016. They studied the chemical composition of these samples, which is also an important indicator of the ambient air quality.

Written by Anjali Marar | Pune |
Updated: January 20, 2021 1:52:09 am
Higher amounts of rainfall means that it washes out greater levels of pollutants. (File)

Rainwater over Pune is alkaline in nature and there are no harmful levels of chemicals capable of triggering acid rain in the region, scientists from the Indian Institute of Tropical Meteorology (IITM) said on Tuesday.

A team of researchers collected rainwater samples from Pashan (urban) and Sinhagad (rural) during monsoon from 2006 to 2016. They studied the chemical composition of these samples, which is also an important indicator of the ambient air quality.

“The samples from Pune and Sinhagad were alkaline in nature. But rainwater collected from Sinhagad was slightly less alkaline than samples from Pune. This was mainly contributed by comparatively lower concentration of ammonium and more concentration of sulphate,” said Pramod Safai, senior IITM researcher, who was part of the study published in Air Quality, Atmosphere and Health.

Rainwater contains sea salt, soil dust, particles of anthropogenic origin and gases from various emissions from either local or distant sources.

Located at an altitude of more than 1,300 metres above mean sea level, Sinhagad enjoys certain advantages over Pashan. “Sinhagad records heavy rainfall during monsoon. Rainwater in itself has several chemicals in the form of aerosols and gases mixed in it. Due to the neutralising effect of ammonium and dust, which contains calcium, acidity of rainwater gets arrested, making the rainwater alkaline,” explained Safai.

Due to lower concentration of dust and pollution levels supported by low population density as compared to the urban location, rainwater collected at Sinhagad was chemically richer. Higher amounts of rainfall meant that it washes out greater levels of pollutants.

Whereas in Pashan, even with higher levels of anthropogenic activities and pollution, the local dust particles keep the rainwater close to alkaline threshold levels. The researchers also tracked the contributory air masses which brought rainfall during the monsoon over the two locations.

“74 per cent of the rain events in Pune and 65 per cent of rain events recorded over Sinhagad were triggered by oceanic air masses brought in from the Arabian Sea,” the study noted.

Sinhagad remains a weekend getaway for Pune residents due to the region’s scenic beauty, the trekking region and Sinhagad Fort. Despite being at a higher altitude, the growing human activities, including tourism and construction, will contribute towards long term atmospheric changes over Sinhagad, which could reflect in rainwater composition, the scientists warned.

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