AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Aerosol Formation Initiated by Nucleation of Radical-Water Complexes
SAMBHAV KUMBHANI, Emily Burrell, Shirts Randall, Jaron Hansen, Brigham Young University
Abstract Number: 171 Working Group: Advances in the Physics and Chemistry of New Particle Formation and Growth
Abstract Aerosols affect climate and human health both directly and indirectly. Atmospheric aerosols are either primary or secondary. Primary aerosol particles enter the atmosphere directly and include sources such as soot, mineral dust, sea salt and pollen. Secondary aerosols form in the atmosphere by the condensation of gases. The formation and growth of secondary particles is typically modeled using nucleation theory. However, the number aerosol particles in the atmosphere predicted by models is smaller than what is actually measured. Radical-molecule complexes may act as an initial nucleating site for particle formation. HO$_2 radical is the most abundant peroxy radical in the atmosphere and forms a strong hydrogen-bonded complex with water. We studied aerosol nucleation through HO$_2-H$_2O complex formation using a flow reaction coupled to a scanning mobility particle sizer (SMPS). We measured the size distribution (between 0.8 and 1000 nm) and concentration of aerosol particles with respect to reaction time, initial concentration of HO$_2 radical, and concentration of water vapor. The experimental work was complimented with high level ab initio studies of the HO$_2-(H$_2O)$_n (n = 1–5) complexes. The computational work provids insight into the Gibb’s free energy, enthalpy, and entropy of complex formation. Both experimental and computational results indicate that HO$_2-H$_2O complex can act as a nucleating agent for new particle formation. Future work will investigate the ability of other radicals to initiate particle formation.