AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Effect of Oxidant Concentration, Exposure Time and Seed Particles on Secondary Organic Aerosol Chemical Composition and Yield
ANDREW LAMBE, Puneet Chhabra, Timothy Onasch, William Brune, James Hunter, Jesse Kroll, Molly Cummings, James Brogan, Yatish Parmar, Douglas Worsnop, Charles Kolb, Paul Davidovits, Aerodyne Research, Inc.
Abstract Number: 327 Working Group: Aerosol Chemistry
Abstract We performed a systematic intercomparison study of the chemistry and yields of secondary organic aerosol (SOA) generated from OH oxidation of a common set of gas-phase precursors in an aerosol flow reactor and several environmental chambers. In the flow reactor, SOA precursors were oxidized using OH concentrations ranging from 2×10$^8 to 2×10$^(10) cm$^(-3) over exposure times of 100 sec. In the environmental chambers, precursors were oxidized using OH concentrations ranging from 2×10$^6 to 2×10$^7 cm$^(-3) over exposure times of several hours. The OH concentration in the chamber experiments is close to that found in the atmosphere, but the integrated OH exposure in the flow reactor can simulate atmospheric exposure times of multiple days compared to chamber exposure times of only a day or so. A linear correlation analysis of the mass spectra and carbon oxidation state of SOA produced in the flow reactor and environmental chambers for OH exposures of approximately 10$^(11) cm$^(-3) sec suggests that the composition of SOA produced in the flow reactor and chambers is the same within experimental accuracy as measured with an aerosol mass spectrometer. This similarity in turn suggests that both in the flow reactor and in chambers, SOA chemical composition at low OH exposure is governed primarily by gas-phase OH oxidation of the precursors, rather than heterogeneous oxidation of the condensed particles. In general, SOA yields measured in the flow reactor are lower than measured in chambers for the range of equivalent OH exposures that can be measured in both the flow reactor and chambers. The influence of sulfate seed particles on isoprene SOA yield measurements was examined in the flow reactor. The studies show that seed particles increase the yield of SOA produced in flow reactors by a factor of 3 to 5 and may also account in part for higher SOA yields obtained in the chambers, where seed particles are routinely used.