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The effect of viscosity and diffusion on the HO2uptake by sucrose and secondary organic aerosol particles

  • Author(s): Lakey, PSJ
  • Berkemeier, T
  • Krapf, M
  • Dommen, J
  • Steimer, SS
  • Whalley, LK
  • Ingham, T
  • Baeza-Romero, MT
  • Pöschl, U
  • Shiraiwa, M
  • Ammann, M
  • Heard, DE
  • et al.

Published Web Location

http://www.atmos-chem-phys.net/16/13035/2016/
No data is associated with this publication.
Abstract

© Author(s) 2016. We report the first measurements of HO2uptake coefficients, γ, for secondary organic aerosol (SOA) particles and for the well-studied model compound sucrose which we doped with copper(II). Above 65% relative humidity (RH), γ for copper(II)-doped sucrose aerosol particles equalled the surface mass accommodation coefficient α = 0.22±0.06, but it decreased to γ = 0.012±0.007 upon decreasing the RH to 17 %. The trend of γ with RH can be explained by an increase in aerosol viscosity and the contribution of a surface reaction, as demonstrated using the kinetic multilayer model of aerosol surface and bulk chemistry (KM-SUB). At high RH the total uptake was driven by reaction in the near-surface bulk and limited by mass accommodation, whilst at low RH it was limited by surface reaction. SOA from two different precursors, α-pinene and 1,3,5-trimethylbenzene (TMB), was investigated, yielding low uptake coefficients of γ < 0.001 and γ = 0.004±0.002, respectively. It is postulated that the larger values measured for TMB-derived SOA compared to α-pinene-derived SOA are either due to differing viscosity, a different liquid water content of the aerosol particles, or an HO2+ RO2reaction occurring within the aerosol particles.

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