AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Ambient Aerosol Volatility Measurements during SOAS, 2013:Thermodenuder Measurements to Constrain Equilibrium and Kinetics of Aerosol Phase Partitioning
PROVAT SAHA, Andrey Khlystov, Andrew Grieshop, North Carolina State University
Abstract Number: 690 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Volatility is an important property of atmospheric aerosols that strongly influences their atmospheric lifecycle. Thermodenuder (TD) is a widely used tool to measure aerosol volatility in both lab and field. Since evaporation of aerosol in TD is dictated by a large number of independent parameters (C*, ΔHvap and γe), it is difficult to constrain all of the volatility parameters with only 1-dimensional (e.g. TD temperature) perturbation to the initial equilibrium. Systematically operating TD systems at varying residence times and at different temperature stepping can provide insights about the evaporation kinetics of aerosol and equilibrium partitioning in the TD. Here, the volatility of ambient aerosol in rural southern US was measured during the Southern Oxidant Aerosol Study (SOAS) ground site near Centerville, Alabama in June and July, 2013. In this study, a temperature-stepping TD (TS-TD) with a long residence time (about 40 s), was used to extract equilibrium properties of ambient aerosol over a range of temperatures (40-180 ºC). Parallel to this, a variable residence time TD (VRT-TD) with a moderately heated activated carbon surface at constant temperature of 90 ºC was run to acquire information about the isothermal evaporation kinetics of aerosol. Simultaneous measurements of aerosol size distributions were collected in reference and thermodenuded lines using parallel SMPS systems. In addition, non-refractory aerosol chemical species mass (e.g. Organic, Sulfate, Nitrate, Chloride and Ammonium) were measured using Aerosol Chemical Speciation Monitor (ACSM) alternating between denuded and reference lines. The VRT-TD data suggest that aerosol equilibrated after very short residence time (< 2 s), in contrast to other ambient observations. Preliminary analysis show that approximately 50% and 90% of total aerosol mass evaporated at TD temperatures of 100 ºC and 180 ºC, respectively. Evaporation varied substantially with ambient aerosol loading and composition and meteorology.