AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Changes in Soot Aggregate Morphology Due to Coatings of Secondary Organic Aerosol from Anthropogenic and Biogenic Precursors
ELIJAH G. SCHNITZLER, Ashneil Dutt, Jason S. Olfert, Wolfgang Jaeger, University of Alberta
Abstract Number: 652 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract The optical properties and climatic effects of soot aggregates depend on their size and shape, which can change during the atmospheric lifetime of the aggregates. For example, vapours can condense onto the surface of aggregates and cause them to collapse, presumably due to surface tension effects. Changes in morphology have previously been observed for aggregates exposed to saturated vapours of sulfuric acid, oleic acid, and a number of other species. Changes in morphology have also been reported for aggregates exposed to oxidation products of alpha-pinene, toluene, and isoprene in smog chamber experiments, in which secondary organic aerosol (SOA) coats the aggregates. We investigated changes in soot aggregate morphology due to coatings of SOA from five precursors (benzene, toluene, ethyl benzene, p-xylene, and limonene) in a series of smog chamber experiments designed to determine if the extent of aggregate collapse depends on precursor species. Soot generated using a McKenna burner was dried, denuded, neutralized, size-selected, and passed into a smog chamber. Once the soot particle concentration reached at least 1000 per cubic centimeter, a given SOA precursor was injected. Hydrogen peroxide was photolyzed to generate hydroxyl radical. During photo-oxidation, coated and denuded particles were alternately sampled by a differential mobility analyzer. The denuded particles decreased in diameter until a final collapsed soot core formed. The difference between the initial and final diameters for 100, 150, 200, and 250 nanometer soot aggregates exposed to SOA from all precursors was measured. As expected, the extent of collapse increases with increasing initial soot aggregate size; however, the extent of collapse does not depend on the identity of the SOA precursor.