Development and Application of Function Group Analysis for Secondary Organic Aerosol Studies
The objective of this dissertation was to develop spectrophotometric methods for functional group analysis of secondary organic aerosol (SOA) and to apply these in conjunction with other methods to studies of the aerosol products formed by oxidation of volatile organic compounds and oxidative aging in model reaction systems representative of the atmosphere.
In Chapter 2 spectrophotometric methods were developed to quantify carbonyl, hydroxyl, carboxyl, and ester groups in samples with compositions typical of oxidized atmospheric organic matter. The methods employ derivatizing agents to convert each functional group to a characteristic colored derivative that is then quantified by spectrophotometry. The effects of molecular structure on quantification were thoroughly evaluated by measuring calibration curves for a large variety of monofunctional and multifunctional compounds. In addition, potential interferences from other compounds containing non-target functional groups were determined and methods developed to eliminate these interferences. Detection limits were also determined.
In Chapters 3 and 4 the functional group analysis methods were used with methods for organic nitrate and peroxide analysis to investigate the chemical composition of SOA formed from OH radical-initiated reactions of n-pentadecane (a model alkane) in the presence of NOx (Chapter 3) and in the absence of NOx (Chapter 4), conditions typical of polluted and clean air. Real-time and offline thermal desorption particle beam mass spectrometry and SOA yield measurements were used in addition to functional group analysis to characterize the SOA. The results of functional group analysis were consistent with the complex array of products expected from the established reaction mechanisms and mass spectrometric data, lending support to the reaction mechanisms currently in use.
In summary, the developed functional group analysis methods are well suited for SOA studies. In the future they can be applied to further studies of complex SOA-forming reactions as well as the relationships between functional group composition and SOA properties such as cloud condensation nucleating activity and toxicity.