Peter Adams Speaks at Gordon Conference for Atmospheric Chemistry
Peter Adams, Associate Professor of Civil and Environmental Engineering and Engineering and Public Policy, gave an invited talk at the Gordon Conference for Atmospheric Chemistry held in Waterville Valley, NH, in August 2009. The talk, entitled "CCN Formation on the Global Scale: Microphysics and Chemistry" discussed the chemistry and physics of cloud condensation nuclei (CCN).
CCN are the subset of airborne particles that grow into cloud droplets when a cloud forms. Without CCN, the atmosphere's relative humidity would reach approximately 400% before water condensed. Instead, the relative humidity in a typical cloud is usually just a fraction of a percent greater than 100% because water easily condenses onto pre-existing CCN particles. The CCN behavior of a particle is governed by its size and composition.
CCN are important to climate change because human activities have increased their concentrations since the Industrial Revolution. For a given amount of condensable water, a cloud with a higher number of CCN tends to have a higher number of cloud droplets, but these cloud droplets tend to be smaller on average. The resulting increase in cloud surface area reflects more sunlight back to space, thus cooling the Earth. The cooling of the planet from increased CCN levels has partly offset global warming due to greenhouse gases.
Prof. Adams's research group has been a leader in describing the physics and chemistry of CCN in global climate models. His Gordon Conference talk highlighted some key research results that emerge from their simulations. A common theme to these results is the importance in understanding how "ultrafine" airborne particles too small to be CCN (having diameters typically less than 100 nm) grow to sizes where they can function as CCN. Some of the key processes that control CCN concentrations on the global scale include the number and sizes of particles from combustion systems, the amount of organic material condensing onto ambient particles, the number of nuclei particles (diameters about 1 nm) formed in the atmosphere and the solubility of organic material found in atmospheric particles.
Nearly 200 Gordon Conferences are held each year on a variety of topics and aim to provide an international forum to discuss research results at the frontiers of each area. Talks at this year's Atmospheric Chemistry conference were limited to 20 invited speakers.