J.-F. Müller, K. Ceulemans, S. Compernolle Belgian Institute for Space Aeronomy, Brussels, Belgium
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Transcript of J.-F. Müller, K. Ceulemans, S. Compernolle Belgian Institute for Space Aeronomy, Brussels, Belgium
J.-F. Müller, K. Ceulemans, S. CompernolleBelgian 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. PeetersKatholieke Universiteit Leuven, Belgium
COOH
COOH
O
CHO
O
COOH
O3, OH, NO3etc.
volatile compounds
semi-volatile compounds
etc.
COOHCOOH
O
CHO
O
COOH
Secondary Organic Aerosol (SOA)
Kp,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
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
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
Secondary chemistry Explicit part of mechanism : degradation down to primary products +
degradation of pinonaldehyde But the degradation down to CO2 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 (RO2, ROOH, RONO2 etc.) is defined, and further subdivided into 4 volatility classes
Aerosol formation: Partitioning theory (Pankow, 1994)
12
,,
1 4
3 3om
on iAvo g i i i
MW a ak
N D
Aerosol radius
Accomodation coefficient (assumed > 0.1)
Adsorption rate:
12
,, 6 0
, 0 ,
10760
10p i on Avo
p ig i om i i L i off om
C k NRTK
C M MW p k MW
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 Müller, 2006)
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 KPP/Rosenbrock as chemical solver
http://www.oma.be/TROPO/boream
Ozone formation: simulation of experiments
Ozone (ppm)
Kamens and Jaoui 2001
SAPRC, Carter et al. 2000
D(O3 -NO) (ppm)
O3 (ppm)
SOA formation: Photooxidation experimentsΔVOC
(ppb)ΔVOC/ NOx
OH:O3:NO3
(% )T (K)
J(NO2) (104 /s)
Nozière et al., 1999
(4 experiments)
300 -
1500
0.09–0.52 100:0:0 298 3.5 (lamp)
Kamens et al., 2001(2 experiments)
~ 980 ~ 2 42:44:13
295 - 315 12-35 (sun)
Hoffman et al., 1997(7 experiments)
19 - 95 0.17–0.78 44:31:20
309 - 321 83 (sun)
Takekawa et al., 2003(6 experiments)
55 – 196
1.5-1.9 53:42:4
283 - 303 40 (lamp)
Ng et al., 2006(1 experiment)
108 1.1 62:22:16
293 10 (lamp)
Presto et al., 2005(8 experiments)
11 – 205
0.3 - 30 6:82:11 295 300 (lamp)
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+R’CHO) has little impact except in high-VOC ozonolysis experiments
Time series
Alpha-pinene decay is well reproduced in all cases
SOA formation occurs too late in the simulation of a few Nozière et al. experiments
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 Nozière et al. experiment
Acids dominant (>50%) in ozonolysis experiments (Presto et al.)
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+R’CHO) 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