IIT Madras-Led International Study Reveals How Human Activity Shapes Aerosols and Climate

Lockdown gave scientists a natural experiment to see how emissions alter cloud formation in India’s coastal regions

Key Findings

• Cloud Condensation Nuclei (CCN) concentrations surged by 80–250% after the COVID-19 lockdown as emissions rebounded.
• New particle formation (NPF) was the main driver of this surge, reshaping aerosol behaviour.
• Organic aerosols, once thought to inhibit clouds, were found to promote cloud formation when abundant.
• Anthropogenic emissions were shown to directly reprogram aerosol–cloud interactions in India’s coastal atmosphere.
• The study provides crucial real-world data to refine global climate models and reduce uncertainties.

Unlocking the Mystery of Aerosols

An international team led by IIT Madras has revealed how human activities strongly influence tiny airborne particles known as aerosols—vital for cloud formation and rainfall. The study, carried out between March and July 2020, focused on India’s coastal regions and found dramatic changes in CCN, the seeds of cloud droplets.

Published in the ACS ES&T Air journal on August 26, 2025, the research provides much-needed real-world data to refine global climate models, which often struggle to account for the complexity of aerosol–cloud interactions.

A Natural Experiment During Lockdown

The COVID-19 lockdown created an unprecedented natural experiment. As air pollution levels fell sharply, scientists observed how aerosols behaved in cleaner conditions—and what happened as emissions slowly returned. Surprisingly, CCN concentrations surged by 80–250% after the lockdown, fueled by more frequent new particle formation.

Lead researcher Prof. Sachin S. Gunthe explained: “Our research shows that anthropogenic emissions strongly shape aerosol behaviour and cloud formation. This challenges current models and opens new pathways to understand climate patterns.”

Challenging Old Assumptions

The study also overturned a long-standing belief about organic aerosols. Traditionally thought to inhibit cloud formation, organic particles were instead found to encourage it when present in large numbers. Despite being less water-attracting than inorganic particles, their sheer abundance made them effective in boosting CCN, ultimately influencing cloud growth and rainfall.

“This shows us that what we once thought hindered cloud formation can, under the right conditions, actually help create clouds,” said Aishwarya Singh, co-author and now at the Max Planck Institute for Chemistry.

Implications for Climate Predictions

These findings highlight the urgent need to combine sophisticated computer models with real-world measurements. “Measurements like ours offer clarity that models alone cannot achieve,” Prof. Gunthe emphasized. “They form the foundation for more accurate climate projections and better policy decisions.”

Dr. M. Ravichandran, Secretary of the Ministry of Earth Sciences, who was not part of the study, called the research “critical information for negotiating future atmospheric dynamics.”

Looking Ahead

The study underscores how human behaviour can rapidly alter atmospheric chemistry, affecting cloud patterns and long-term climate. It also sets the stage for more accurate climate strategies rooted in both empirical data and advanced modelling.

As co-author Prof. R. Ravikrishna summed up: “We cannot predict the future of our climate without rigorously understanding the present.”

This research shows that the atmosphere is deeply sensitive to human action—reminding us that individual and collective choices ripple all the way up into the clouds.