AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Emissions of Secondary Organic Aerosol Initiated by Surface Reactions between Ozone and Squalene
Chunyi Wang, MICHAEL WARING, Drexel University
Abstract Number: 243 Working Group: Indoor Aerosols
Abstract Squalene is a low volatility compound that is prevalent on human skin and on indoor surfaces due to human desquamation. Ozone/squalene surface reactions initiate the generation of numerous volatile and semivolatile products, some of which may lead to secondary organic aerosol (SOA) formation. To investigate that possibility, 13 steady state chamber experiments were conducted to measure the SOA formation due to ozone reactions with squalene sorbed to glass, at chamber ozone mole fractions of 57–500 ppb for two relative humidity (RH) conditions of 20 and 50%, in the absence of seed particles. The size distributions, mass and number secondary emission rates (SER), aerosol mass fractions (AMF), and aerosol number fractions (ANF) of formed SOA were quantified. The surface AMF and ANF are defined as the change in SOA mass or number formed, respectively, per ozone mass consumed by ozone/squalene surface reactions. All experiments but one exhibited appreciable nucleation and subsequent SOA mass formation. Mass formation parameters increased monotonically with ozone, more notably for the higher RH experiments. Similar to the traditional gas phase AMF, the surface AMF was a function of the chamber aerosol concentration, and a multiproduct model was fit to the results using ‘volatility basis set’ parameters. Number formation was strong at low ozone/low RH conditions, implying that these conditions favored nucleation. Based on an estimate of the time scales for desorption of compounds formed on the surface, nucleating species are thought to be formed by reactions that initiated on the surface and are completed in the gas phase after the initial product desorption. The mass formation results were extrapolated to explore the importance of this mechanism in real indoor spaces; likely environments influenced are those with high occupant densities and low air exchange rates.