A model study of laboratory photooxidation experiments of mono- and sesquiterpenes M. Capouet and J.-F. Müller Belgian Institute for Space Aeronomy L. Vereecken and J. Peeters Katholieke Universiteit Leuven, Belgium R. Winterhalter and G. Moortgat Max Planck Institute for Chemistry, Germany

Plan of presentation The BOREAM box model The BOREAM box model Simulation results of α-pinene photooxidation experiments A preliminary model study β-caryophyllene: mechanism development and first simulation results A preliminary model study β-caryophyllene: mechanism development and first simulation results Conclusions Conclusions

Biogenic compounds Oxidation and RElated Aerosol formation Model Photolysis calculation package based on TUV (Madronich, 1990) Gas-phase model Inorganic/organic standard chemistry α-pinene/pinonaldehyde + OH/O 3 /NO 3 : Explicit mechanism down to the formation of low-yield (<5%) stable products (e.g. Peeters et al.,2001 & Vereecken and Peeters, 2004) Simplified representation for the degradation of these minor products Gas-phase model Inorganic/organic standard chemistry α-pinene/pinonaldehyde + OH/O 3 /NO 3 : Explicit mechanism down to the formation of low-yield (<5%) stable products (e.g. Peeters et al.,2001 & Vereecken and Peeters, 2004) Simplified representation for the degradation of these minor products Gas/aerosol partitioning model Based on a kinetic approach (Kamens and Jaoui, 2001) Partitioning coefficients (K p = K on /K off ~ 1/p L ) estimated using a vapor pressure prediction method (Capouet and Müller, ACP, 2006) No heterogeneous/condensed phase reactions (so far) Gas/aerosol partitioning model Based on a kinetic approach (Kamens and Jaoui, 2001) Partitioning coefficients (K p = K on /K off ~ 1/p L ) estimated using a vapor pressure prediction method (Capouet and Müller, ACP, 2006) No heterogeneous/condensed phase reactions (so far) BOREAMBOREAM 4000 reactions & 800 species

How can we describe the further oxidation of the stable (minor) products? On the basis of the oxidation mechanism generator from Aumont et al. (2005) : Number of explicit reactions/species which should be considered for α-pinene >> 10 6 : Large majority of the reactions concerns the further oxidation of primary products and cannot be readily characterized from experimental or theoretical studies  Necessary to establish adequate protocols to represent their impact

Parameterization for the secondary chemistry in BOREAM: OH-oxidation : Based on SARs ( Neeb, 2001; Kwok and Atkinson, 1995) and theoretical calculations ( Peeters and co- workers ) Photodissociation : Each oxygenated functionality is treated separately

OH hv BOREAM MCM hv OH k OH = 6.65 x cm 3 /molec./s H2OH2O Example of pinonic acid : k OH = 9.1 x cm 3 /molec./s + CH 3 CO H2OH2O H2OH2OH2OH2O

Parameterization for the secondary chemistry in BOREAM: Minor products resulting from the secondary chemistry are represented by generic species defined according to the carbonnumber and chemical functionalities Explicit products with yield < 5 % Generic chemistry Explicit chemistry of α-pinene & its major products OH/NO 3 /O 3 hv OH-oxidation : Based on SARs ( Neeb, 2001; Kwok and Atkinson, 1995) and theoretical calculations ( Peeters and co- workers ) Photodissociation : Each oxygenated functionality is treated separately

Comparison with photooxidation experiments

Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio Mixing ratio 10 (lab.)293 OH: 62 O 3 : 22 NO 3 : Nga et al., (lab.)283 OH: 53 O 3 : 42 NO 3 : Takekawa et al., (solar)315 OH: 44 O 3 : 31 NO 3 : Hoffman et al., Temp. (K) 161 (lab.) OH: 6 O 3 : 82 NO 3 : Presto et al., (solar) OH: 42 O 3 : 44 NO 3 : Kamens et al., (lab.)OH: Nozière et al.,1999 J(NO 2 ) (10 4 /s)Oxidants % Δα-pin. / NOx Δα-pin. (ppb) Typical photooxidation experiments modeled

Yields obtained after 1-3 hours 25 % of the stable products formed via generic chemistry

VMR of α-pinene VMR of SOAMolar yield of SOA Y Y Y Time (h) Nozière et al. Kamens et al. Nga et al.

Aerosol phase composed of multifunctional compounds. Acids constitute only a minor fraction of the modeled aerosol, because their gas-phase yields are small in BOREAM : Objective theoretical grounds are still lacking for the formation pathways of the most common acid condensables (e.g. pinic/hydroxy pinonic acid).

(α-pinene = 30 ppb) Effect of NOx concentration

Sesquiterpenes: A preliminary model study

Modeling laboratory experiments of β-caryophyllene photooxidation β-caryophyllene oxidation in BOREAM (1800 reactions / 500 species) : Preliminary gas-phase oxidation mechanism based on the oxidation of α- and β-pinene and on products identified in the laboratory ( Jaoui and Kamens, 2003; Winterhalter et al., 2006) Protocols describing the gas-phase chemistry and the partitioning of the products in the α-pinene oxidation model are applied Simple mechanism of ozone uptake by particulate unsaturated products ( Mochida et al,. 2006; Zahardis et al., 2006)

O3O3 O3O3 O O + O 3 O O γ=1 x O O particulate phase

O O + O 3 O O O O particulate phase + + Low volatility products Surface process limited by the reactive uptake of ozone  hypothesis of rapid diffusion in the condensed phase

Model vs. Laboratory data Promising results ! Reactive uptake of ozone not negligible at the time scale of the laboratory experiment: - 30% of the particulate products have reacted after 3 hours - However no significant increase of the aerosol mass is modeled First Results

α-pinene  The products formed in the gas-phase photooxidation have sufficiently low vapor pressures to partition in the condensed phase and produce SOA in significant amount in photooxidation experiments.  The SOA formed is largely made of multifunctional products susceptible to oligomerize and enhance SOA yields after longer times.  Theoretical studies did not validate primary formation route for pinic acid and hydroxy pinonic acid so far. β-caryophyllene  The partitioning of large amounts of unsaturated products suggests a rapid uptake of ozone followed by in situ oligomerization. Conclusions