Chemical Pathways Leading to Organic Aerosol Formation from the Atmospheric Oxidation of Alkanes

University Of California-Riverside, Riverside CA

Investigators

Abstract

The primary objective of this experimental program is to elucidate the detailed chemical mechanisms leading to the formation of secondary organic aerosol (SOA) from atmospheric photooxidation of alkanes. Alkanes comprise the largest class of volatile organic compound (VOC) emissions from anthropogenic sources, and appear to be a significant contributor to urban SOA. Alkane-derived compounds present an ideal system for exploring the basic gas-phase chemical reaction mechanisms involved in the formation of low-volatility, condensable compounds. The general approach for this project will be to investigate the gas- and particle-phase products of the hydroxyl (OH) radical-initiated reactions of selected alkanes and of their first- and potentially second- (and later) generation products in large-volume environmental chambers. A combination of demonstrated, state-of-the-art techniques, including thermal desorption particle beam mass spectrometry (TDPBMS), atmospheric pressure ionization mass spectrometry, and gas chromatography-mass spectrometry with derivatization, will be used to analyze gas-phase and particle-phase products in real-time as well as off-line, in order to identify and quantify successive generations of products and follow the chemical evolution of SOA formation and growth. The alkanes to be investigated include n-decane and a number of its isomers. Studies of SOA formation in the presence of seed particles of different compositions will investigate the potential role of particle-phase polymerization reactions. This research will help to determine the importance of alkane photooxidation in atmospheric SOA formation and the chemical mechanisms by which this occurs. The results will improve current understanding of the fate of alkanes, which are a major component of the atmosphere, and aid in the development of more sophisticated atmospheric models of SOA formation and behavior. These types of models are widely used to evaluate the potential effects of aerosols on global climate change, air pollution and visibility, and human health, which are all important problems confronting society. This project will also make it possible to educate a number of graduate and undergraduate students, who in turn will have the opportunity to educate others, in the area of atmospheric chemistry as well as on more general environmental issues.