The effect of viscosity and diffusion on the HO2 uptake by sucrose and secondary organic aerosol particles

We report the first measurements of HO2 uptake 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...

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Bibliographic Details
Published in:Atmospheric chemistry and physics 2016-10, Vol.16 (20), p.13035-13047
Main Authors: Lakey, Pascale S J, Berkemeier, Thomas, Krapf, Manuel, Dommen, Josef, Steimer, Sarah S, Whalley, Lisa K, Ingham, Trevor, Baeza-Romero, Maria T, Pöschl, Ulrich, Shiraiwa, Manabu, Ammann, Markus, Heard, Dwayne E
Format: Article
Language:English
Subjects:
Accommodation
Accommodation coefficient
Acids
Aerosol particles
Aerosols
Coefficients
Copper
Copper compounds
Data analysis
Diffusion effects
Experiments
Gases
Humidity
Mathematical models
Moisture content
Multilayers
Particulates
Relative humidity
Secondary aerosols
Smog
Sucrose
Sugar
Surface reactions
Trimethylbenzene
Uptake
Viscosity
Water
Water content
α-Pinene
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Summary:We report the first measurements of HO2 uptake 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 coefficientα = 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 + RO2 reaction occurring within the aerosol particles.
ISSN:1680-7316
1680-7324
DOI:10.5194/acp-16-13035-2016