J.-F. Müller, K. Ceulemans, S. Compernolle Belgian Institute for Space Aeronomy, Brussels, Belgium...

of 14 /14
J.-F. Müller, K. Ceulemans, S. Compernolle Belgian Institute for Space Aeronomy, Brussels, Belgium AGU Fall Symposium, Dec. 2007 Factors influencing SOA yields in the simulation of α-pinene photooxidation experiments L. Vereecken, J. Peeters Katholieke Universiteit Leuven, Belgium
  • date post

    18-Dec-2015
  • Category

    Documents

  • view

    213
  • download

    0

Embed Size (px)

Transcript of J.-F. Müller, K. Ceulemans, S. Compernolle Belgian Institute for Space Aeronomy, Brussels, Belgium...

  • Slide 1
  • J.-F. Mller, K. Ceulemans, S. Compernolle Belgian Institute for Space Aeronomy, Brussels, Belgium AGU Fall Symposium, Dec. 2007 Factors influencing SOA yields in the simulation of -pinene photooxidation experiments L. Vereecken, J. Peeters Katholieke Universiteit Leuven, Belgium
  • Slide 2
  • O 3, OH, NO 3 etc. volatile compounds semi-volatile compounds etc. Secondary Organic Aerosol (SOA) K p,i (partitioning coefficients) etc. Experiments indicate that heterogeneous or particle-phase chemistry generates high- molecular weight compounds, enhancing SOA formation Previous model studies found necesary to increase the partitioning coefficients by several orders of magnitude in order to match SOA yields from laboratory experiments
  • Slide 3
  • Oxidation by OH mechanism based on advanced theoretical calculations Peeters et al. 2001; Vereecken and Peeters, 2004; Fantechi et al., 2002 important updates from Vereecken et al., PCCP, 2007
  • Slide 4
  • Ozonolysis mechanism still preliminary, but theoretical work is in progress pathways proposed so far to explain some key observed products (pinic acid, hydroxy pinonic acid) have been demonstrated to be negligible As a consequence, the yield of organic acids is too low in this mechanism Capouet et al., JGR, in press
  • Slide 5
  • Secondary chemistry Explicit part of mechanism : degradation down to primary products + degradation of pinonaldehyde But the degradation down to CO 2 would require maybe billions of reactions (Aumont et al.) Combination of semi-generic chemistry (for high-yield compounds) and generic chemistry (for the rest) Semi-generic compounds are lumped compounds for which the carbon number and all functionalities are defined, not their precise structure Generic compounds are lumped compounds for which one functionality (RO 2, ROOH, RONO 2 etc.) is defined, and further subdivided into 4 volatility classes
  • Slide 6
  • Aerosol formation: Partitioning theory (Pankow, 1994) Aerosol radius Accomodation coefficient (assumed > 0.1) Adsorption rate: Gas- and particulate phase concentrations at equilibrium Organic aerosol concentration Adsorption and desorption rates Saturation vapour pressure Partioning coefficient: obtained from a group contribution method (Capouet and Mller, 2006)
  • Slide 7
  • Overall alpha-pinene mechanism 5000 reactions, 1300 compounds (including the gas- aerosol partitioning reactions) Capouet et al., J. Geophys. Res., in press complete mechanism can be explored at http://www.oma.be/TROPO/boream/boreammodel http://www.oma.be/TROPO/boream/boreammodel KPP/Rosenbrock as chemical solver
  • Slide 8
  • http://www.oma.be/TROPO/boream
  • Slide 9
  • Ozone formation: simulation of experiments Ozone (ppm) Kamens and Jaoui 2001 SAPRC, Carter et al. 2000 D(O 3 -NO) (ppm) O 3 (ppm)
  • Slide 10
  • SOA formation: Photooxidation experiments VOC (ppb) VOC / NOx OH:O 3 :NO 3 (% ) T (K) J(NO 2 ) (10 4 /s) Nozi re et al., 1999 (4 experiments) 300 - 1500 0.090.52100:0:02983.5 (lamp) Kamens et al., 2001 (2 experiments) ~ 980~ 242:44:13 295 - 315 12-35 (sun) Hoffman et al., 1997 (7 experiments) 19 - 950.170.7844:31:20 309 - 321 83 (sun) Takekawa et al., 2003 (6 experiments) 55 196 1.5-1.953:42:4 283 - 303 40 (lamp) Ng et al., 2006 (1 experiment) 1081.162:22:16 29310 (lamp) Presto et al., 2005 (8 experiments) 11 205 0.3 - 306:82:11295300 (lamp)
  • Slide 11
  • Results: SOA yields Stark contrast with previous modeling studies which required orders of magnitude enhancements of the partitioning coefficients in order to match observed SOA yields Simulations with additional acid formation channels in ozonolysis mechanism lead to better agreement in some (not all) low-VOC experiments Simulations with additional particle- phase association reactions (ROOH+RCHO) has little impact except in high-VOC ozonolysis experiments
  • Slide 12
  • Time series Alpha-pinene decay is well reproduced in all cases SOA formation occurs too late in the simulation of a few Nozire et al. experiments
  • Slide 13
  • SOA composition Particulate compounds are multifunctional Generic compounds are significant but not dominant in modeled SOA at sampling time Hydroperoxides make up 25% of compounds in a high- NOx Nozire et al. experiment Acids dominant (>50%) in ozonolysis experiments (Presto et al.)
  • Slide 14
  • Conclusions Low-volatility hydroperoxides from OH-initiated oxidation contribute significantly to SOA even in presence of NO Theoretical and laboratory work needed to elucidate origin of acids in ozonolysis Particle-phase association reactions (ROOH+RCHO) have only a small impact, except in some conditions (SOA yields enhanced by about 1/3 in high-VOC Presto et al. experiments); more laboratory work needed to investigate the elementary steps Huge uncertainties in vapor pressures and activity coefficients, chemistry Near future: calculate activity coefficients, fine-tune the mechanism and the vapor pressures in order to improve agreement In case of satisfactory results, develop a reduced mechanism and SOA parameterization for implementation in a global model