Influence of Non-polar Amino Acids on Phase Transitions of Aerosol Particles

KIRAN REDDY PITTA, Miriam Freedman, The Pennsylvania State University

     Abstract Number: 226
     Working Group: Aerosol Physics

Abstract
Phase transitions in atmospheric aerosol particles have a significant impact on heterogeneous chemistry, hygroscopicity, and cloud formation. The composition of the particles influences aerosol phase transitions. A large fraction of particles contain both organic and inorganic compounds, with organic matter constituting 20 to 90% of the particle mass. Organonitrogen compounds are estimated to compose up to 30% of the total organic fraction. Despite this significant presence, the phase transition properties of aerosol particles involving organonitrogen species have not been thoroughly researched. Amino acids, a type of organonitrogen compound found in the atmosphere, were chosen for the study. Non-polar amino acids were used, where the amino acids were mixed with either 2-methylglutaric acid or 1,2,6-hexanetriol (model oxidized organic compounds) and ammonium sulfate (inorganic salt) to study the effect of the concentration of amino acids on the phase transition properties of droplets using an optical microscope. A suppression of separation relative humidity was observed with an increase in the concentration of amino acids, while an increase in efflorescence relative humidity was observed in the case of relatively low solubility amino acids (leucine, isoleucine, and valine). A three-phase morphology was detected for some systems, with the efflorescence of amino acids competing with the phase separation of the 2-methylglutaric acid/ammonium sulfate and 1,2,6-hexanetriol acid/ammonium sulfate systems. These studies are important in understanding the impact of organic-organic interactions on the phase transition properties of aerosol particles, which have consequences for heterogeneous chemistry in the atmosphere.