An Indian Institute of Technology Madras (IIT Madras) led International Study has unveiled significant findings surrounding the interaction of aerosols, which are tiny suspended particles in air essential for cloud formation and precipitation.

This is a critical area of research that continues to generate the largest uncertainties in climate change predictions.

The study, conducted between March and July 2020, unveiled the profound influence of human activities on cloud-forming aerosols, also called ‘Cloud Condensation Nuclei’ (CCN), along India’s coastal regions.

The implications of this study are profound. With climate models heavily reliant on computer simulations, the established measurements and findings provide empirical data that can help refine these models, thereby reducing uncertainties.

The findings were published in the prestigious American Chemical Society's ES&T Air Journal (https://doi.org/10.1021/acsestair.5c00180) in a paper co-authored by Prof. Sachin S. Gunthe, Coordinator, Center for Atmospheric and Climate Sciences, IIT Madras, Aishwarya Singh, a former PhD student at IIT Madras who is now a post-doctoral researcher at the Max Planck Institute for Chemistry in Mainz, Germany, Prof. R. Ravikrishna, faculty, IIT Madras, and other National and International researchers.

Highlighting the importance of such research, Dr. M. Ravichandran, Secretary, Ministry of Earth Sciences, Government of India and a renowned climate scientist who was not part of this research, said, “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.”

This research challenges common beliefs about the role of organic aerosols and provides critical data to reduce uncertainties in global climate models, while emphasising the importance of real-world measurements. As the world strives to mitigate climate change, the research team at IIT Madras observed a startling 80-250% increase in CCN concentrations following the COVID-19 lockdown.

This surge, as clearly shown by the study, resulted from more frequent new particle formation (NPF), a process where aerosol particles are formed from gases through complex chemical processes in the atmosphere, post-lockdown, as human-caused emissions slowly rebounded.

This surge in freshly formed particles was the direct driver of the increase in CCN concentration. These findings highlight how human behaviour directly affects the planet’s climate systems. The shift from predominantly cleaner marine air to polluted continental sources post-lockdown indicates the complex relationship between human activity and aerosol dynamic behaviour.

The research also found that anthropogenic organic matter was the dominant factor in the growth of these new particles, challenging the common belief that organic particles inhibit cloud formation. While it is true that organic particles can create surface films that affect cloud droplet formation, this study found that a significant increase in the number of organic particles can actually promote cloud formation.

In coastal India, for instance, an increase in these organic particles led to a rise in cloud condensation nuclei (CCN), which are essential for cloud development. Despite their relatively lower ability to attract water compared to inorganic particles, the sheer number of organic particles allowed them to contribute effectively to cloud formation. This means that even particles we thought might hinder cloud growth can, under certain conditions, play a crucial role in creating clouds, ultimately influencing weather patterns and climate.

Elaborating on this research, lead researcher and atmospheric scientist Prof. Sachin S. Gunthe, also a faculty in the Environmental Engineering Division, Department of Civil Engineering, IIT Madras, said, “Our research reveals that anthropogenic emissions strongly influence aerosol behaviour, particularly in how they form clouds. These findings challenge existing models and propose new avenues for understanding how human activities shape climate patterns.”

Further, Aishwarya Singh, a former PhD student at IIT Madras who is now a post-doctoral researcher at the Max Planck Institute for Chemistry in Mainz, Germany, said, “We witnessed firsthand how the drastic reduction in air pollutants during the lockdown provided a unique ‘natural experiment’. Our observations show that a cleaner atmosphere can be highly sensitive to new emissions, altering the aerosol-cloud interactions significantly, which can have a profound impact on climate predictions.”

“Measurements like ours, drawn from real-world conditions, offer clarity that computer-based models alone cannot achieve,” emphasized Prof. Sachin Gunthe. “This new science provides the foundation for more accurate climate projections, which is essential for informing policy and environmental management,” he added

The researchers are optimistic that these insights will help climate scientists reassess their models and approach to studying aerosol effects on climate change. Thus, these findings accentuate that understanding climate change necessitates a dual approach—both implementing sophisticated models and emphasizing the importance of empirical evidence.

As Prof. R. Ravikrishna, one of the co-authors and a faculty at IIT Madras, remarked, “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.”

This study not only highlights the importance of empirical field data in climate research but also underscores the potential for impactful changes stemming from human activity. As the scientific community seeks to navigate and mitigate climate change, this enhanced understanding of aerosol-cloud interactions may serve as a cornerstone to developing more accurate strategies for managing our environmental future.

The hope is that this research will catalyse further studies and elevate public awareness of the significant effects individual and collective actions have on our climate. Through a commitment to blending empirical data with modern technology, researchers aim to forge a path toward sustainable climate solutions.