Global Mercury Observation System which is observing 67 places with a device called ambient mercury vapour an... Read More

Four years after rapper Sofia Ashraf’s song ‘Kodaikanal Won’t’ brought mercury pollution in Kodaikanal back in public discourse, a study by Institute for Ocean Management (IOM), Anna University has found that Chennai’s air is contaminated with gaseous mercury and the levels are more than that found in Kodaikanal or in several cities studied across the world.

Globally, an average of 1.5ng/ m 3 of gaseous mercury is found in the atmosphere; In Chennai, it ranges between 3.5ng/m 3 to 8.5ng/m 3 .

“In Kodaikanal, we found that the concentration of natural gaseous mercury is 1.53ng/m 3 . The readings in Chennai were way above the natural concentration and during some seasons it reached more than 20ng/m 3 . But further study is needed to find out whether power plants, industries and the sea cause a spike in gaseous mercury,” said IOM director S Sreenivasalu. The study has been on since 2016.

Naturally, gaseous mercury goes into the air through evaporation and transpiration. In Chennai, the highest concentration of mercury in the air was found between 3am and 8am. “In the wee hours, the boundary of troposphere comes down from about 10km above earth to 8km. This could be the reason for mercury concentration levels being higher early morning,” Sreenivasalu said. Gaseous mercury concentration is usually highest near the surface and decreases with altitude.

The study is part of the Global Mercury Observation System which is observing 67 places with a device called ambient mercury vapour analyser. It absorbs air from the atmosphere and removes moisture. The air is then sent into two cartridges where the level of mercury is analyzed.

“Only when data from both the cartridges concur, we take the results,” said Sreenivasalu.

Scientists have found a correlation between wind speed, direction and concentration of gaseous mercury in the atmosphere. “We found seasonal variations in its concentration. It is more in summer but during winter it falls as evaporation is less,” said Manikanda Bharath K, one of the researchers involved in the project.

Bharath said besides industrial pollution, proximity to the sea, which is a huge natural reserve of mercury, could be a reason for concentration of gaseous mercury in the city’s air. Researchers have collected soil and water samples to ascertain the presence of mercury on the surface. IOM is also procuring three mercury analyzers. However, it is yet to decide on their deployment.

