Researchers from 8 countries led by IIT-Madras study climate impact of power plant emissions

As India went under a strict lockdown in March 2020 induced by Covid-19 pandemic forcing industries to close and vehicles off the roads, a team from the Indian Institute of Technology-Madras with researchers from across the globe sat down to study anthropogenic emissions from different sectors under relatively cleaner conditions in India.

The team found that the coastal city of Chennai experienced a substantial reduction in local anthropogenic pollution, such as traffic and industries, during the first month of the lockdown, but the full operation of the Neyveli Lignite Corporation (NLC) led to formation of a new particle and growth due to SO2 emissions from the plant located 200 kms away from the city.

When the power plant plume intersected the observation site, there were high sulfate concentrations and associated new particle formation, which was followed by rapid particle growth. The sulfate-rich particles rapidly grew into CCN size, and were observed to have high hygroscopicity, thus largely increasing the CCN concentration.

The study concluded that implementing aggressive measures to reduce particulate pollution originating from traffic and various industrial sources within coastal regions such as Chennai might lead to outcomes that work against the intended goals and stressed on the need for exploration of alternative strategies to address air pollution effectively.

Led by Prof Sachin S Gunthe from the Centre for Atmospheric and Climate Sciences at IIT-M, the goal of the study by 27 researchers from 17 distinct institutions was to assess the impact of specific emission sources, mainly from the power plant to understand the underlying processes of aerosol formation and its impact on cloud formation and climate.

Gunthe said the first question that arises when someone talks about climate change is how much will the temperature increase and there is a large uncertainty in calculating that because unlike the greenhouse gases which can be measured, there has never been an exact quantification that whether the clouds in the atmosphere cool the surface.

“Because of the mixing of aerosols before the study, it was difficult for climate modulars to understand the exact implication of the power plant emission on the climate forcing. As regular aerosol emission was at its minimum during Covid-19, we could find out how much it contributes to climate forcing,” Gunthe told DH.

The findings of the study are reported as a scientific research paper published this week in the reputed peer-reviewed NPJ Climate And Atmospheric Science.

“This study's outcomes imply that the existing strategies aimed at reducing PM2.5 levels from traffic and industries in India's polluted coastal clusters need thorough revaluation,” the Prof said, adding that the study found that the conversion of SO2 emissions from power plants into particulate matter contributes to an elevated mass load of aerosols rich in sulfates with high cloud-forming potential within the atmosphere.

The study revealed a remarkable event where long-range transport of sulphur dioxide (SO2) gas emitted from the Neyveli power plant resulted in new particle formation (NPF) in Chennai, generating particles generally known as ‘secondary aerosols.’

The findings demonstrated that the SO2 plume from the power plant resulted in high particulate sulphate concentrations and subsequent particle growth, which grew into the size relevant and required for the cloud formation exhibiting a high ability to uptake water.

The researchers successfully demonstrated that when local sources of anthropogenic emissions stop, the SO2 emissions from power plants may amplify the mass of PM2.5 through the formation of new particles, which contradicts common assumptions.

The study emphasized that, therefore, under cleaner conditions with reduced human activities, the availability of low-volatility vapours of specific gases increases the chances of formation and growth of new aerosol particles, as opposed to the business-as-usual scenario where these low-volatile gases may condense on pre-existing aerosol particles resulting from human activities in an urban setup like Chennai.