Measured and Modeled Secondary Organic Aerosol Products and Yields from the Reaction of n-Hexadecane + OH/NO x

Secondary organic aerosol (SOA) is formed by condensation of products of the oxidation of volatile organic compounds (VOCs) that are emitted from natural and anthropogenic sources and is known to impact atmospheric chemistry, climate, and human and environmental health. Although alkanes are an important VOC emission and their gas-phase atmospheric chemistry is quite well understood, laboratory studies of SOA formation have mostly been limited to measurements of SOA yields and identification of products. Here, we describe the results of an environmental chamber study of the composition of SOA formed from the OH radical-initiated reaction of n-hexadecane (the linear C-16 alkane) in the presence of NOx under aging conditions that lead to first- and second-generation products. Using a combination of filter sampling, derivatization, liquid chromatography with UV detection, and chemical ionization-ion trap mass spectrometry, we have identified and quantified most of the SOA products with yields greater than similar to 1%. The measured composition is in reasonable agreement with predictions of a simple kinetic model that employs the well-established gas-phase chemical reaction mechanism, gas-particle and gas-wall partitioning, particle-phase reactions, and secondary gas-phase reactions with OH radicals that form second-generation products. The results demonstrate the utility of the experimental methods for identifying and quantifying SOA products, and the model could serve as a useful framework for developing simple models for other alkane reactions after considering the effects of carbon number and structure on key reaction branching ratios and product vapor pressures and also humidity.