Rahul Somvanshi
A study from the Indian Institute of Technology Madras measured how human activities affect cloud-forming particles along India’s coast. Published in ACS ES&T Air (August 2025), the research tracked cloud condensation nuclei (CCN) during and after COVID-19 lockdowns in 2020.
The IIT Madras-led research team, with first author Aishwarya Singh and corresponding author Prof. Sachin S. Gunthe, recorded CCN concentration increases of 80-250% as human-caused emissions rebounded after lockdown restrictions eased. This rise stemmed from more frequent new particle formation (NPF) events – when gases convert to aerosol particles through atmospheric chemistry.
“We witnessed firsthand how the drastic reduction in air pollutants during the lockdown provided a unique ‘natural experiment’,” said Aishwarya Singh, former PhD student at IIT Madras and current post-doctoral researcher at Max Planck Institute for Chemistry. “Our observations show that a cleaner atmosphere can be highly sensitive to new emissions, altering the aerosol-cloud interactions.”
Contrary to common expectations, anthropogenic organic matter emerged as the primary driver of particle growth. While organic particles typically attract water less effectively than inorganic ones, their substantial quantity allowed them to contribute effectively to cloud formation. The study also tracked a shift from cleaner marine air masses to more polluted continental sources as restrictions eased.
“Our research reveals that anthropogenic emissions strongly influence aerosol behaviour, particularly in how they form clouds,” Prof. Gunthe explained. “These findings challenge existing models and propose new avenues for understanding how human activities shape climate patterns.”
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Dr. M. Ravichandran, Secretary at the Ministry of Earth Sciences and a climate scientist not involved in the research, noted: “Aerosol-cloud interactions are intrinsically complicated, and these findings underscore that human activities can dramatically influence underlying processes. This is critical information for negotiating future atmospheric dynamics.”
The study utilized instruments including CCN counters and aerosol spectrometers at coastal monitoring sites to measure cloud-forming particles. Details about specific instrument settings and measurement parameters are available in the paper’s methods section. Researchers collected comprehensive data on particle size distributions, chemical composition, and formation rates between March and July 2020.
Prof. R. Ravikrishna, study co-author and IIT Madras faculty member, stated: “We cannot predict the future of our climate without rigorously understanding the current state of our environment. Measurements provide an essential context to refine and enhance climate models.”
“Measurements like ours, drawn from real-world conditions, offer clarity that computer-based models alone cannot achieve,” added Prof. Gunthe.
For the general public, this research shows how quickly our atmosphere responds to changes in human activity. The CCN rebound following the resumption of anthropogenic emissions after lockdown indicates that changes in human emissions can rapidly alter aerosol concentrations. While these tiny particles remain invisible to the naked eye, they play a crucial role in cloud formation and can influence precipitation, though this study did not measure rainfall directly. The study shows aerosol concentrations and CCN activity changed on timescales from days to months during the lockdown/unlock period, underlining the responsiveness of atmospheric composition to emission changes.
The study results, methodology details, and supplementary information are available via the ACS ES&T Air Journal (DOI: 10.1021/acsestair.5c00180). The research measured cloud-forming aerosol behaviour at coastal sites between March and July 2020 and recorded the CCN concentration changes during the post-lockdown period as anthropogenic emissions resumed.
