AA Blog2: Assigned Reading:

Particulars of Particle Formation

When we look up during the day and see clouds, many people may not think much about them.

We may already know that every cloud droplet once formed from a pre-existing aerosol particle. However, the exact formation mechanism and composition is not exactly clear, hence this study. The formation of new particles is termed aerosol nucleation much debate surrounds the constituents of their formation.

From the Nature Geoscience Advance Online Publication, this article by Jeffery Pierce brings light to the formation of atmospheric aerosols. According to cloud chamber experiments, a mixture of vapors, as well as ions formed by galactic cosmic rays, contribute to the particle formation recipe (Pierce, 1).

This is a schematic showing the influence of ammonia, organics and ions on aerosol nucleation.

In (a) sulfuric acid vapor is said to be a key contributor to aerosol nucleation because of their strong correlation between sulfuric acid concentrations and aerosol nucleation rate. However, theory suggests that small clusters of this molecule should evaporate, and thus that nucleation should not occur, under conditions near the earth’s surface. In (b) ammonia, gas phase ions are generated by galactic cosmic rays and certain nitrogen-containing organic compounds stabilize molecular clusters of sulfuric acid, preventing evaporation. As shown in (c), stabilization therefore favors the development of new particles. If enough material condenses into the new particles (d), they will grow to sizes where they can affect clouds and climate. However, if the new particle coagulates with a larger particle (e), the aforementioned is not true. The competition between growth and coagulation determines the impact of new particles on clouds and climate.

Although this was a short article I enjoyed reading through it and learning new information in the fundamentals of aerosol formation.