Scientists tracing the concentration, size and evolution of aerosol particles smaller than 3 nanometers at an urban location in India have found the frequent formation of sub-3nm aerosol particles in the atmosphere.

What is Aerosol Nucleation?

• The formation of small molecular clusters of sub-3nm size is technically called aerosol nucleation, and subsequent growth of these newly formed clusters to the large sizes is called atmospheric new particle formation (NPF).
• NPF occurs everywhere in the terrestrial troposphere, and therefore it is a large source of aerosol numbers to the atmosphere.
• Though extensively studied globally using field observations, laboratory experiments and modelling approach, it is largely unexplored in India.

What has the new research found?

• The research showed that a pool of sub-3nm particles is often present in the atmosphere, but how fast these clusters grow depends on various factors.
• The scientists observed that only half of these events showed newly formed molecular clusters growing past 10 nm size.
• Thus particle size distributions display a conventional banana-shaped aerosol growth, which is indicative of regional NPF event.

Role of Sulphur

• The team found a strong positive correlation between sub-3nm particle concentrations and sulphuric acid concentrations, confirming the potential role of sulfuric acid in the formation of sub-3nm particles.
• While NPF often starts with sulphuric acid in the atmosphere, sulphuric acid alone fails to explain observed particle formation and growth rates in the atmosphere.
• Other vapours such as ammonia, amines and organics play a crucial role in the growth of newly formed particles.
• This has critical importance as a major fraction of these newly formed particles can reach to sizes of cloud condensation nuclei where they have climatic impacts.

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