AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
The Photolytic Processing of Organic Aerosols through Carbonyl Photochemistry
SANDRA BLAIR, Scott Esptein, Sergey Nizkorodov, University of California, Irvine
Abstract Number: 63 Working Group: Aerosol Chemistry
Abstract Photochemistry is the primary driving force behind most chemical processes occurring in the atmosphere. Secondary organic aerosol (SOA) contains highly oxidized, multifunctional, organic compounds, many of which are photolabile, even under the near-UV excitation conditions representative of the lower atmosphere. Because of the high prevalence of carbonyl compounds in SOA, its photochemistry can be expected to be driven in part by the well-known photochemical reactions of carbonyls such as Norrish and Yang mechanisms. Therefore, investigating model carbonyls, such as linear chain aldehydes, provides valuable information on the mechanism and rate of photochemical processes occurring in SOA. Short chain aldehydes have been studied extensively over the last few decades in the gas-phase. The importance of condensed-phase photochemistry in the atmosphere has not been recognized until recently. The extent to which the photolysis quantum yield is suppressed in the condensed-phase is not well-known. There are many types of organic matrices that can be used to mimic the environment of SOA particles; the pure condensed-phase form of an aldehyde is a convenient representation of either a liquid or solid organic matrix (depending on the size of the aldehyde). A C-11 aldehyde, undecanal, provides a perfect model for this carbonyl photochemistry because it melts slightly below room temperature. The photochemistry of undecanal is investigated in several different environments: (1) liquid melt; (2) frozen solid; and (3) vapor phase. Products of condensed-phase experiments are analyzed with gas chromatography mass spectrometry, Fourier transform infrared spectroscopy, and ultraviolet-visible spectroscopy. Proton transfer reaction mass spectrometry is used for real time high resolution and sensitive gas-phase photochemical measurements. The main conclusion of this study is that condensed-phase photolysis of aldehydes is not significantly hindered relative to the gas-phase photolysis, suggesting that photochemistry of aldehydes in SOA should be just as important as photochemistry of gas-phase aldehydes.