AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Thermodynamic Properties of Weakly Dissociating Organic Acids Found in Atmospheric Aerosols
LUCY NANDY, Cari Dutcher, University of Minnesota, Twin Cities
Abstract Number: 214 Working Group: Aerosol Chemistry
Abstract Organic acids make up a significant fraction of the organic mass in atmospheric aerosol particles. Predictions of gas-liquid-solid equilibrium partitioning of the organic acid by thermodynamic modeling and measurements is critical for accurate determination of atmospheric particle properties and processes at temperatures and relative humidities relevant to the atmosphere. Statistical mechanics based on an existing adsorption isotherm model for capturing thermodynamic properties of multicomponent aqueous solutions over the entire concentration range (Dutcher et al. JPC 2011, 2012, 2013, Ohm et al. JPC 2015), is applied to partially dissociating organic acids to understand atmospheric aerosol water content. In addition to the modeling approach, water loss of aerosol particles is measured by microfluidic experiments to parameterize the model.
In this work, weakly dissociating semi-volatile organic acids like dicarboxylic acids are treated as a mixture of non-dissociated organic solute (HA) and dissociated organic solute (H+ + A-) considering a static solute concentration ratio (Nandy et al. JPC – under review). It was found that the apparent dissociation was greater than that predicted by known dissociation constants alone, emphasizing the effect of dissociation on activity coefficient predictions. The acids are then treated with varying solute concentration ratios to study the degree of dissociation over the entire concentration range. This work results in predictive correlations for estimation of organic acid and water activities for which there is little or no activity data. The model is complemented with experiments by biphasic microfluidics to measure efflorescence relative humidities and supersaturation behavior by generating and trapping aqueous droplets.