AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Potential Factors Limiting Growth of Nucleated Particles into Cloud Condensation Nuclei
DANIEL WESTERVELT, Jeffrey Pierce, Peter Adams, Carnegie Mellon University
Abstract Number: 181 Working Group: Aerosol Nucleation: From Clusters to Nanoparticles
Abstract Aerosol nucleation is an important source of particle number in the atmosphere. However, in order to become cloud condensation nuclei (CCN), freshly nucleated particles must undergo significant condensational growth while avoiding coagulational scavenging. Previous work used observationally-based constraints to determine that, even when accounting for multi-day growth, boundary layer nucleation contributes just 2-14% of the total number of particles larger than 100 nm in a variety of locations. This work builds on that finding by quantifying the feedbacks associated with the small nucleation-CCN sensitivity. Using the GEOS-Chem-TOMAS global aerosol microphysics model, we simulate 15 different nucleation and growth scenarios and analyze individual nucleation events over one simulated year. Nucleation rate parameterizations include ternary nucleation (with multiple tuning factors), activation nucleation (with multiple pre-factors), binary nucleation, and ion-mediated nucleation. In previous work, GEOS-Chem-TOMAS was thoroughly evaluated against observed nucleation events at five locations: Pittsburgh, Hyytiälä, Atlanta, St. Louis, and San Pietro Capofiume. In the present work we calculate daily nucleation rates, growth rates, coagulation sinks, condensation sinks, sulfuric acid concentrations, particle survival probabilities, and CCN formation rates between the 15 different nucleation and growth sensitivity cases. We hypothesize that our small CCN sensitivity is explained by faster nucleation rates leading to a larger sink of condensable vapors which in turn limits survival and growth to CCN. Quantitatively, we find that a factor of 36 increase in the annual average nucleation rate between two particular nucleation simulations at Hyytiälä leads to only a factor of 1.6 increase in CCN formation from nucleation and a 13% increase in total CCN concentrations. The dampening in CCN changes appears to be caused by an increase in the condensation sink and an accompanying decrease in growth rates and condensable vapor concentrations. Work is ongoing to test more sites and parameterizations.