AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
How Do Secondary Organic Aerosols Influence Cloud Condensation Nuclei? Insights from a Global Model Employing Detailed Aerosol Microphysics
Peter Adams, MARGUERITE COLASURDO MARKS, Carnegie Mellon University
Abstract Number: 599 Working Group: Aerosols, Clouds, and Climate
Abstract Atmospheric aerosols influence global climate by serving as cloud condensation nuclei (CCN), and the complexities of aerosol-cloud interactions dominate the forcing uncertainty in current climate models. Organic aerosol (OA) species play an important role in the CCN budget, as they are ubiquitous in the atmosphere and help drive condensational growth of particles to climate-relevant sizes. Not only does condensation of organics onto a particle increase its mass (and thus its survival probability), though: OA can contribute solute to particles, increasing the likelihood of activation into CCN; and the presence of surface-active organic compounds may decrease particle surface tension enough to significantly increase cloud droplet formation. Understanding the relative magnitude of these effects is necessary to focus further studies on the most important aspects of OA.
The goal of this modeling study is to examine the sensitivity of CCN levels to organic-aerosol-mediated influences. We simulate 2009 using the global chemical transport model GEOS-Chem with TOMAS aerosol microphysics using kappa-Kohler theory. We evaluate CCN sensitivity to: OA budgets, organic hygroscopicity, and condensation and coagulation parameterizations. The influence of surface-active species and the “salting-out” effect are also discussed.
We find that for a range of plausible assumptions regarding emissions and mechanisms, ultrafine growth (rather than primary emissions) dominates CCN production. The largest influence on CCN is the overall secondary organic aerosol (SOA) budget. Results suggest that a moderate portion of the influence of SOA is simply due to condensing mass increasing particles' survival probability -- that is, CCN levels are sensitive to the amount, but not necessarily the type of SOA. We hope that, by identifying the model processes to which CCN are most sensitive, our results will help determine the most promising directions for future research in this area.