AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Insight into Particle Growth Rates and Controls from Two Years of SMPS and HTDMA Data
MANASI MAHISH, Don Collins, Texas A&M University
Abstract Number: 300 Working Group: Advances in the Physics and Chemistry of New Particle Formation and Growth
Abstract Data from a scanning mobility particle sizer (SMPS) and a humidified tandem differential mobility analyzer (HTDMA) have been used to study the controls on growth of recently formed particles at the DOE Southern Great Plains site in Oklahoma. New particle growth events during 2009 and 2011 that spanned at least several hours were identified and both the particle size distributions and size-resolved hygroscopicity distributions from each episode were fitted with lognormals. Time series profiles of the resulting growing mode median particle diameters and hygroscopic growth factors were then fitted using appropriate mathematical forms and their time-dependent slopes used to quantify the rates of change of particle size and hygroscopicity, reflecting the overall addition of mass and the net properties of that mass, respectively. These changes were also translated into those of the hygroscopicity parameter, kappa, to better link with other datasets and to more easily partition the contributions of generic aerosol components to the observed growth. After subtracting the change attributable to coagulation, the remaining growth was assumed to result from condensation of a more hygroscopic inorganic component and a less hygroscopic organic component having a kappa estimated from available aerosol chemical speciation monitor (ACSM) data describing the PM1 aerosol organics. The rates of addition of those two condensable components were related to requisite gas phase concentrations to better separate the hourly, daily, and seasonal variations in responsible atmospheric chemistry of interest from interference from the quantifiable size-dependence of the growth rate. Both the frequency of the observed growth events and the particle growth rates during them have summer maxima and winter minima. Partitioning of the more and less hygroscopic condensing species often varies during an event, with the more hygroscopic component contributing relatively more during the daytime. Both representative case studies and averaged profiles will be presented.