AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
A novel kinetics mechanism for particle formation from methanesulfonic acid, amines and water.
MATT DAWSON, Mychel E. Varner, Veronique Perraud, Micheal, J. Ezell, Benny Gerber, Barbara J. Finlayson-Pitts, University of California, Irvine
Abstract Number: 773 Working Group: Aerosol Nucleation: From Clusters to Nanoparticles
Abstract Aerosol formation in the atmosphere has been shown to be strongly dependent on sulfuric acid (H2SO4, SA), with recent indications that ammonia and amines play an important role. Typically, nucleation rates from this system are calculated according to a single-step kinetics equation whose exponential dependence on gas-phase SA concentration can be used with nucleation theory to determine the number of molecules of SA in the critical cluster. However, models still tend to underpredict nucleation rates in the atmosphere, indicating that there may be other sources of atmospheric aerosols or that the equations used to describe nucleation may need to be revisited, particularly for multicomponent nucleation. Here we present a novel multi-step kinetics mechanism appropriate for multicomponent nucleation based on results from laboratory studies of particle formation from methanesulfonic acid (CH3SO3H, MSA), amines and water. MSA is formed alongside SA in the oxidation of organosulfur compounds in the atmosphere and amines have a variety of both biogenic and anthropogenic sources. Experiments were performed in a unique, slow flow, large volume flow-tube reactor at 295 K and 1 atm under conditions of varying relative humidity. Particle size distributions are measured using a scanning mobility particle sizer (SMPS) and gas-phase MSA concentrations are determined by filter collection and subsequent analysis by LC-MS. Also presented are results from ab initio calculations of the smallest clusters of MSA, amines and water. Indications from the experimental and model results that nucleation proceeds via a complex kinetics mechanism along with atmospheric implications are discussed.