Development and Application of Functional Group Analysis for secondary organic aerosol

SUKON AIMANANT (1) and Paul J. Ziemann (1)

(1) University of California, Riverside

     Abstract Number: 383
     Last modified: November 9, 2009

Abstract
Secondary organic aerosols (SOA) are important due to their impact on human health and global climate by acting as cloud condensation nuclei. They are formed from the oxidation of volatile organic compounds in the atmosphere. Reactions of volatile organic compounds in the atmosphere with the oxidants OH, NO$_3, and O$_3, lead to a variety of oxygenated products including aldehydes, alcohols, carboxylic acids, peroxides, organic nitrates, and others. Many of these compounds are multifunctional, resulting in low volatility and high polarity, so they often condense to form SOA. Since functional groups are major factors in determining compound reactivity and other properties, characterization of functional group composition of SOA will be useful for understanding their effects on human health and the environment. Therefore, the objectives of this project are to develop the methods to quantify these functional groups and to quantify functional group composition in SOA for modeling of atmospheric reaction products and for developing models of water-uptake and cloud condensation nucleating activity of SOA. Because peroxide and organic nitrate analyses were developed by previous students in our lab, in the present work, I am developing the methods for quantification of carboxyl, carbonyl, hydroxyl and ester groups. The methods for analysis of carbonyl, carboxyl, hydroxyl and ester groups have been developed. These functional groups were analyzed by colorimetric methods. Carbonyl and carboxyl groups were derivatized by dinitrophenylhydrazine and 2-nitrophenylhydrazine hydrochloride respectively. Under basic conditions, these derivatives produced color that can be measured by spectrophotometer at a specific wavelength. The methods were also used to quantify the composition of carbonyl and carboxyl groups in products from the reaction of oleic acid aerosol particles with nitrate radicals. The results from these analyses were consistent with those obtained using a HPLC coupled to a UV diode array detector and a high-resolution mass spectrometer with electrospray ionization. For hydroxyl group analysis, 4-nitrobenzoyl chloride was used to derivatize hydroxyl groups. Derivatives were measured by spectrophotometer after being extracted into hexane. Ester group analysis has been developed by conversion of ester groups to hydroxamic acid which can then form ferric hydroxamate with ferric chloride and can be measured by spectrophotometer. These methods that have been developed were applied to quantify the functional group compositions in SOA products from the reactions of some alkanes, for example, pentadecane and cyclopentadecane, with hydroxyl radicals under dry condition and 50% relative humidity. In addition, they will be used to analyze functional group composition in the products from the reactions of some alkenes, carboxylic acids, carbonyls and alcohols with hydroxyl radicals, ozone or nitrate radicals for modeling of atmospheric reaction products and for developing models of water-uptake and cloud condensation nucleating activity of SOA.