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Title: Effect of oxidant concentration, exposure time, and seed particles on secondary organic aerosol chemical composition and yield

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 a Potential Aerosol Mass (PAM) continuous flow reactor and several environmental chambers. In the flow reactor, SOA precursors were oxidized using OH concentrations ranging from 2.0 × 10 8 to 2.2 × 10 10 molec cm -3 over exposure times of 100 s. In the environmental chambers, precursors were oxidized using OH concentrations ranging from 2 × 10 6 to 2 × 10 7 molec 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. In most cases, for a specific SOA type the most-oxidized chamber SOA and the least-oxidized flow reactor SOA have similar mass spectra, oxygen-to-carbon and hydrogen-to-carbon ratios, and carbon oxidation states at integrated OH exposures between approximately 1 × 10 11 and 2 × 10 11 molec cm -3 s, or about 1–2 days of equivalent atmosphericmore » oxidation. This observation suggests that in the range of available OH exposure overlap for the flow reactor and chambers, SOA elemental composition as measured by an aerosol mass spectrometer is similar whether the precursor is exposed to low OH concentrations over long exposure times or high OH concentrations over short exposure times. 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.« less
 [1] ;  [2] ;  [1] ;  [3] ;  [4] ;  [4] ;  [5] ;  [5] ;  [5] ;  [2] ;  [2] ;  [5]
  1. Boston College, Chestnut Hill, MA (United States); Aerodyne Research Inc., Billerica, MA (United States)
  2. Aerodyne Research Inc., Billerica, MA (United States)
  3. Pennsylvania State Univ., State College, PA (United States)
  4. MIT (Massachusetts Inst. of Technology), Cambridge, MA (United States)
  5. Boston College, Chestnut Hill, MA (United States)
Publication Date:
Grant/Contract Number:
SC0006980; SC0011935; FG02-05ER63995
Published Article
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 15; Journal Issue: 6; Related Information: CHORUS Timestamp: 2015-03-18 07:27:01; Journal ID: ISSN 1680-7324
European Geosciences Union
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); National Science Foundation (NSF). Atmospheric Chemistry Program
Country of Publication:
OSTI Identifier: