AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Interpreting Thermal Denuder Data with an Optimizing Comprehensive Instrument Model
JAMES HITE, Kate Cerully, Athanasios Nenes, Georgia Institute of Technology
Abstract Number: 343 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract In this study, we develop a method of determining the volatility distribution of an aerosol sample through the use of a fully characterized thermal denuder (TD) instrument model. The first model component resolves the temperature and parabolic laminar flow field of the TD while the second resolves the mass transfer associated with aerosol evaporation inside the instrument. This is advantageous as the model can in effect be applied to TDs of varying geometry, requiring only a few direct measurements of the centerline temperature profile at certain temperatures which are then scaled to any desired temperature setting. The evaporation module (mass transfer component) simulates the evolution of aerosol with a given condensed-phase volatility distribution in the TD using a volatility basis set (VBS) approach as described in (Donahue et. al. 2006).
A volatility tandem differential mobility analyzer (VTDMA) setup is used to gather data which are then interpreted by the modeling framework. Measured particle number concentration and size (organic aerosol mass concentration, C$_(OA)) before the TD inlet are used to determine aerosol partitioning into the VBS which then, along with the flow characteristics, drives the mass transfer in the model. An iterative optimization routine coupled with the TD instrument model is utilized to determine the bulk volatility distribution of a given aerosol sample by minimizing a cost function with number of terms proportional to the number of observations. The TD model is tested against data collected for laboratory-generated aerosol composed of single compounds and mixtures thereof. In benchmarking the model, properties of each species derived from model analysis of TD experiments are compared against literature values (e.g., saturation concentrations and density). The retrieval of the volatility distribution of mixtures generated in the lab is thoroughly assessed for consistency with the single-compound experiments and the published literature.