AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
An Investigation on Secondary Organic Aerosol Induced Restructuring in Soot Aggregates
Kaiser Leung, Elijah G. Schnitzler, Ramin Dastanpour, Steven Rogak, Wolfgang Jager, JASON S. OLFERT, University of Alberta
Abstract Number: 103 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Two sets of photo-oxidation experiments were conducted to investigate the restructuring of soot aggregates induced by secondary organic aerosol (SOA) coating and its humidity dependence. The experiments involved soot aggregates generated from three sources, namely an ethylene premixed burner, an inverted diffusion burner, and a diesel generator. Soot aggregates were treated by denuding then size-selected by a differential mobility analyzer and injected into a smog chamber, and subsequently exposed to SOA using p-xylene as a precursor. The change in mobility of aggregates between the initial and final structures displayed a linear dependence on the number of primary particles in the aggregate. The linear relationship could allow modelers to predict the evolution of aggregate morphology induced by SOA coating. In the second set of experiment, the relative humidity (RH) dependence of the restructuring of aggregates induced by SOA coatings was investigated. Soot aggregates were generated using an ethylene premixed burner, classified by mobility diameter and injected into a smog chamber. The aggregates were then exposed to SOA coatings using p-xylene as a precursor and subsequently subjected to one of the RHs: < 12, 20, 40, 60, 85%. At RH < 12%, a uniform increase in mobility diameter with increasing coating mass was observed, indicating that the coating was too viscous to induce aggregate restructuring. At RH above 20%, restructuring of aggregates was observed in the form of a decrease in mobility diameter with increasing coating mass. Interestingly, the degree of restructuring increases with increasing RH, indicating that elevating humidity decreases coating viscosity and increases surface tension. Appreciable water uptake by the SOA coating was observed for RH above 60%, and the hygroscopicity parameter for SOA coating generated from p-xylene was determined. This result has significant implications on atmospheric restructuring of soot aggregates induced by SOA coatings.