AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Volatility and Gas-Particle Partitioning of Organic Acids in a Ponderosa Pine Forest
LAXMINARASIMHA YATAVELLI, Harald Stark, Samantha Thompson, Joel Kimmel, Douglas Day, Pedro Campuzano-Jost, Michael Cubison, Joel A. Thornton, John Jayne, Douglas Worsnop, Jose-Luis Jimenez, University of Colorado, Boulder, CO
Abstract Number: 658 Working Group: Aerosol Chemistry
Abstract We present diurnal variations, volatility, and gas-particle partitioning of organic acids measured in a ponderosa pine forest during July and August 2011 as part of the Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen - Rocky Mountain Biogenic Aerosol Study (BEACHON-RoMBAS; http://tinyurl.com/BEACHON-RoMBAS). Data was collected using a micro-orifice volatilization impactor chemical ionization high-resolution time-of-flight mass spectrometer (MOVI-HRToF-CIMS; Yatavelli et al., submitted, 2012) with acetate as the reagent ion. The volatility measurement is based on collection of submicron aerosol particles in the MOVI (Yatavelli and Thornton, AS&T, 2010) in parallel with gas-phase analysis, followed by temperature-programmed thermal desorption (TPTD) of the collected aerosol.
Estimation of ambient aerosol volatility is based on an empirical estimation following a method similar to that developed by Chattopadhyay and Ziemann (Anal. Chem. 2001) and Faulhaber et al. (AMT 2008) for other TPTD techniques. and calibrated using known semivolatile and low-volatility organic acid mixtures. The log of the vapor pressure of each compound is shown to be strongly related to the inverse of the desorption temperature for standards spanning 6 orders of magnitude in vapor pressure. A shift in the calibration curve when compared to other techniques is attributed to differences in time available for evaporation and physical arrangement of the particles on the aerosol collection surface. Positive Matrix Factorization (PMF) of individual TPTD spectra and of the time series of TPTD spectra reveal several components with reproducible differences of volatility and mass spectra, which are compared to the components derived from a co-located Aerodyne aerosol mass spectrometer (AMS) with volatility information using a thermal denuder (Huffman et al. AS&T 2008). The correlation of elemental composition and volatility is also explored. Particle fraction is shown to increase with compound carbon number, with qualitative behavior consistent with partitioning theory.