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Watching tiny particles in a Finland forest

Ph.D. students Alessandro Franchin and Mikko Äijälä in front of the aerosol measurement cabin at the SMEAR II measurement station in Hyytiälä.
[Photo courtesy of Juho Aalto]

All over the world, tiny airborne particles from volcanoes, dust, pollution and other sources float around in the atmosphere. New field studies in a boreal forest in Hyytiälä, Finland and laboratory experiments reveal how these tiny particles, called atmospheric aerosols, are formed from gas molecules, a new study appearing in the journal Science reports.

The findings shed light on the role new aerosol particle formation may have on climate. Aerosols are born in their environment, rather than being transported intact from the land, the sea, or space.

These aerosols result from a growth process that begins with atmospheric molecules and clusters, progressing to larger and larger sizes as they acquire other molecules, clusters, and particles.

In the 90s scientists were already finding hints of atmospheric particle formation, but it was impossible to know the exact mechanism, since they could not measure particles small enough to see the beginnings of the process.

Markku Kulmala at the University of Helsinki and colleagues developed sensitive new techniques that allow these tiny seeds to be detected and counted, allowing them to map out the process of aerosol formation in detail.

The researchers found that the initial steps of aerosol formation begin with clusters smaller than two nanometers in diameter, and that sulfuric acid and organic molecules were critical components of the particle growth process.

The researchers found that sulfuric acid and organic molecules like carbon join together to form a critical cluster, which grows to become an aerosol particle.

The build-up of a cluster that is stable enough to continue grow is key to aerosol formation. Understanding how aerosols form is crucial to understanding the effect of these particles on climate change.