Effect of the Hydroxyl Group on Yields and Composition of Organic Aerosol Formed from OH Radical-Initiated Reactions of Alcohols in the Presence of NOx

The effect of a hydroxyl group and its position on the yields of secondary organic aerosol (SOA) formed from OH radical-initiated reactions of the 1- to 5-decanol isomers, 1- and 2-undecanol isomers, and n-decane in the presence of NOx was investigated in a series of environmental chamber experiments. SOA composition was also measured using liquid chromatography, mass spectrometry, and infrared spectroscopy, and gas-phase aldehydes were measured using gas chromatography and proton transfer reactionmass spectrometry. It was observed that all decanol isomers formed SOA of a similar composition, which consisted of products similar to those known to be formed from the reaction of n-decane but with an added hydroxyl or keto group. SOA yields measured for the decanol isomers were all higher than the yield from n-decane because of the general lowering of product vapor pressures by the added hydroxyl group, but they decreased monotonically as the hydroxyl group moved from the end of the molecule to the middle. This isomeric trend can be explained by the effect of the position of the hydroxyl group on the fraction of first-generation products formed through pathways involving alkoxy radical isomerization and is consistent with the yields of these products estimated using a kinetics model. Products formed by these pathways tend to have low volatility and, thus, partition into particles, whereas products formed by the major competing pathways are more volatile. The results demonstrate the need to understand not only the effect of functional groups on volatility but also the effect of their location on volatile organic compound oxidation products and mechanisms to accurately predict SOA yields.