Secondary Organic Aerosols: Development and Application of New Techniques in Chamber and Field Experiments

Secondary organic aerosols (SOA) have detrimental effects on human health and can influence the Earth’s climate by altering radiative forcing. Their sources, fates, and chemical composition across the globe, however, remain poorly constrained. A better understanding is necessary to improve predictive air quality models and enable effective mitigation strategies. This thesis presents advances in instrumentation and technique for the analysis of secondary organic aerosols, and applies them to laboratory and field studies. First, this work describes a new SOA formation pathway in which isoprene formed low volatility gas-phase compounds that condensed onto preexisting aerosol. Results from environmental chamber experiments and a field measurement campaign identified product elemental formulas from chemical ionization mass spectrometry measurements (CIMS). It also produced SOA mass yields for the new pathway and estimated its importance in the atmosphere. The development of a method to quantify the loss of gaseous compounds to the Teflon walls of chambers using real-time measurements is described. The method used short bursts of light to produce oxidants in situ, which in turn produced a several gas-phase products with differing volatilities. In the subsequent absence of aerosol and oxidants, the gas-phase products were observed to decay, with the only possible fate being absorption by the chamber walls. The time scale of this process was short (\u3c 700 s) enough to be on the order of other processes in SOA chamber experiments and is thus important enough to necessitate accounting for. Additional experiments are described in which the above method is used with different aerosol seed surface areas to quantify the effect of wall losses on aerosol mass yield. Finally, we demonstrate the application of ion mobility spectrometry-mass spectrometry (IMS–MS) to the simultaneous characterization of the elemental composition and collision cross section of organic species in the gas and particulate phases. Time-resolved measurements (5 min) of oxidized organic molecules were obtained with IMS–MS during the 2013 Southern Oxidant and Aerosol Study (SOAS) ambient field campaign in rural Alabama. The ambient IMS–MS signals are consistent with laboratory spectra obtained from single-component carboxylic acids and multicomponent mixtures of isoprene and monoterpene oxidation products