AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Effect of Thermal Denuding on Soot Aggregates Structure
JANARJAN BHANDARI, Swarup China, Timothy Onasch, Lindsay Renbaum-Wolff, Paul Davidovits, Eben Cross, Adam Ahern, Manvendra Dubey, Claudio Mazzoleni, Michigan Technological University
Abstract Number: 326 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Soot particles are formed during incomplete combustion of carbonaceous materials and are fractal-like aggregates of carbonaceous spherules. After exposure to the atmosphere, these aggregates can undergo structural changes (e.g., coating and compaction), which in turn can affect their optical properties. One of the common approaches used to measure the effect of coating on soot optical properties is to measure absorption and scattering values in ambient air and then measure them again after removing the coating using a thermal denuder. Results of these measurements, using a thermal denuder are interpreted by making two assumptions: 1) all and only the coating material is removed from soot, 2) the pre-existing refractory soot structure is left unaffected.
In this study, we investigated the validity of the second hypothesis by studying the effect of thermal denuding on soot samples that had been generated in controlled conditions with a minimal coating and assessing whether the refractory soot particles were restructured (compacted) or not. We investigated five sets of nascent soot samples before and after thermal denuding. The samples were collected during the Boston College Experiment II and IV. More than 1200 soot particle micrographs from a Scanning Electron Microscope were used to quantify morphological parameters like roundness, convexity and fractal dimension. Our investigation shows only minimal restructure of the fresh soot during the thermodenuding, supporting the validity of the second hypothesis.