UC Irvine

Atmospheric aerosol is known to have a direct effect on the radiative forcing of the climate by absorbing and scattering light and an indirect effect by acting as cloud condensation nuclei. Organic aerosol (OA), sometimes the major contributor to atmospheric aerosol, contains highly oxidized, multifunctional, low vapor pressure organic compounds. Carbonyls play a significant role in the photochemistry of secondary organic aerosol (SOA) as the near-UV absorption spectra of SOA are dominated by the C=O π*←n transition. SOA 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 a model carbonyl, such as a linear chain aldehyde, in an environment that mimics SOA should provide valuable information on the mechanism and rate of photochemical processes occurring in SOA. The pure form of an aldehyde will act as its own SOA-like organic matrix. The quantum yield of photolysis may be suppressed in the condensed-phase, but might still be significantly high to make photolysis relevant. A C₁₁ aldehyde, undecanal, is investigated in this thesis as a model for this carbonyl photochemistry in OA. Undecanal photolysis was investigated at room temperature in liquid and gas phases. Products were analyzed with gas chromatography mass spectrometry or proton transfer reaction mass spectrometry. The products, quantum yields, and rate constants of undecanal in each environment were compared. Results suggest that the loss of carbonyls due to photolysis in the condensed-phase should be just as important as the photochemistry in the gas-phase.