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Climate, air quality, and particles

Written by Shunsuke Nakao, SoGES 2013-2014 Sustainability Leadership Fellow, and Postdoctoral Fellow in the Department of Atmospheric Science.

Particulates in the atmosphere (aerosol) are everywhere, although they are too small to be seen with the naked eye (from nano-meter to micron scale). If you take one mL of air from outside, the chances are that there are thousands of liquid or solid suspended particles. Some are emitted from sources as is (e.g., soil dust); some are produced in the atmosphere through chemical reactions; some are alive or once alive (bioaerosol).

Do aerosol help us or harm us? – It’s complicated. They are air pollutant (e.g., PM2.5); however, without aerosol, there will be no clouds (water needs something to condense onto). They act as a sunshade by reflecting some sunlight back into space, as well as seeding clouds. The "cooling effect" by aerosol is estimated to mask approximately half of the warming effect by green house gases (with a large uncertainty) (IPCC 2007, 2014). The important role of the scientific community is to improve the understanding of the link between emissions and their impacts (air quality and climate change). My research focus has been on the fundamental interaction between gas, particle, and cloud.

One of the research topics I am interested in is the role of water in the atmosphere. Importance of cloud chemistry has been recognized for decades (e.g., sulfate formation); some gaseous compounds dissolve into water and react within water, leaving behind aerosols after evaporation of clouds. Similar processes may also occur in wet aerosols. Recently, another potentially important process emerged. To explain this, let me ask you a simple question - What happens if you dilute peanut butter with water? It gets soft. Something like this may be occurring in the atmosphere. Historically, aerosol particles are treated either as liquid or solid. However, recent studies suggest something in between may be important (Virtanen et al., Nature, 2010). Water may be helping softening the peanut-butter-like material in the atmosphere, impacting their physics (e.g., diffusion within gooey particles) and chemistry.

Next time you see clouds, I hope you can imagine tiny particles that formed each cloud droplet. Are they really like peanut butter? We will figure it out.

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