Formation of Organic Films on Sulfuric Acid Solutions at Upper Troposphere and Lower Stratosphere Aerosol Acidities

Abstract

The effects of atmospheric aerosols on climate remain uncertain, especially where aerosol chemical composition is not well known. Chemical analysis of aerosols in the upper troposphere (UT) and lower stratosphere (LS) show sulfuric acid (40-80 wt. %) and water as the major components. However, recently, the presence of organic molecules was also reported in UT/LS aerosols which could produce a broad spectrum of chemical reactions that have the potential to alter the aerosol climate properties, so experiments were performed to examine these reactions. Propanal, individually or in mixtures with glyoxal and/or methylglyoxal, combined with sulfuric acid formed highly colored surface films. Since surface films would control aerosol climate properties, the goals of this work are to determine the chemical composition of the films and to determine the effects of aging, organic mixture, and acidity on film composition and formation rates. Films and solutions were analyzed by attenuated total reflectance-FTIR, 1 H NMR and UV-Vis spectroscopies. Results show that aldol condensation products (mainly 2-methyl-2-pentenal and 1,3,5-trimethylbenzene) and acetals (mainly 2,4,6triethyl-1,3,5-trioxane and longer-chain linear polyacetals) are the major species in films formed from propanal. In mixtures of multiple organics, cross-reactions between propanal and glyoxal and/or methylglyoxal were also observed. These results are used to assess the potential for organic films to affect the climate properties of UT/LS aerosols. v 1.