Forming Cloud Droplets – Interaction of Organic and Inorganic Aerosols


The growth of atmospheric particles to form cloud droplets influences climate through indirect effects on cloud brightness and lifetime and changes in precipitation patterns. The influence of organic material on cloud condensation nuclei (CCN) activity is important and challenging given that organic material can comprise a dominant fraction of particle mass but CCN are generally a complex molecular mixture. Often, less active organic material is mixed with more active inorganic material (mainly sulfate) in a single CCN particle, so we need to understand the CCN activity of mixed materials, especially those involving secondary organic aerosols formed from reaction products of volatile organic compounds in the atmosphere. BER-funded researchers at Harvard investigated the CCN activity of material resulting from the photo-oxidation of isoprene, the most abundant non-methane hydrocarbon in the atmosphere, mixed with ammonium sulfate, the dominant inorganic aerosol component. Their findings suggest that over regions dominated by high biogenic emissions (e.g., the Amazon Basin), the CCN activity of particles can be simply and accurately represented in large-scale atmospheric and climate models using a model that employs a single suite of parameters for biogenic secondary organic components in conjunction with parameters representing inorganic species.


S.M. King, T. Rosenoern, J.E. Shilling, Q. Chen, Z. Wang, G. Biskos, K.A. McKinney, U. Poeschl, and S.T. Martin, “Cloud droplet activation of mixed organic-sulfate particles produced by the photooxidation of isoprene,” Atmospheric Chemistry and Physics, 2010, 10, 3953-3964.