1. Parameterization of SOA formation for α-pinene, based on a detailed mechanism
Karl Ceulemans– Steven Compernolle – Jean-François Müller
Belgian Institute for Space Aeronomy, Brussels, Belgium
Eurochamp 2 Workshop, Manchester, 2011

2. Outline BOREAM: Detailed model for α-pinene SOA
Simulations of smog chamber experiments
10-product model parameterization including ageing

3. BOREAM : explicit model for α-pinene SOA
Gas phase reaction model with additional generic chemistry and aerosol formation module
10000 reactions, 2500 compounds
Using KPP solver
Capouet et al. (2008), Ceulemans et al. (2010)

4. Explicit chemistry Based on advanced theoretical calculations and SARs
Oxidation by OH, O3 and NO3
Oxidation products react with OH or photolyse (now also in aerosol phase)
Vapour pressure method: Capouet & Müller (2006)

5. Generic chemistry
Semi-generic: carbon number and functional groups
Generic: carbon number, vapour pressure classes (11) and 1explicit functional group
Second generation oxidation products lumped into semi- generic and generic products
10 carbons
1 alcohol &
2 hydroperoxide
LA10HPP
LX9cONO2
Implicit parent structure, with pvap,im

6. Smog chamber Photo-oxidation
low-NOx experiments (Ng et al. 2007)
α-pinene and O3 given in Valorso et al. (2011)
Initial: 330 ppt NO, 330 ppt NO2 , 4 ppb O3 , blacklights
α-pinene decay well-reproduced
ozone : reasonable agreement, sensitive to assumptions!

7. Smog chamber Photo-oxidation: SOA evolution
for Ng et al exp. 1 (low NOx):
SOA mass yields are overestimated: experimental SOA yield is 40%, BOREAM simulation: 60%

8. Smog chamber Photo-oxidation: SOA composition
Molar composition for Ng et al. (2007) exp. 1 (low NOx):
SOA is dominated by hydroxy dihydroperoxides
Particle phase chemistry of hydroperoxides?

9. Model performance: Photo-oxidation*
two low-NOx experiments, (Ng et al. 2007) ; somewhat overestimated
most SOA yields within factor 2

10. 10-product parameter model
5 scenarios:
OH (low and high-NOx )
O3 (low and high-NOx )
NO3 (high-NOx)
Products fit to full model simulations with ageing
Diurnal cycle for VOC, OH, HO2 and O3 ; deposition
SOA equilibrium after 12 days

11. Two-product model parameterizations
Odum (1996)
Y : SOA mass yield
M0 : absorbing organic mass
αi : mass stoichiometric coefficient of product i
Ki : Pankow (1994) absorption
equilibrium constant

12. Temperature dependence of parameters
Absorption equilibrium constant:
Stoichiometric coefficient
0°C
30°C

13. 10-product model parameters
scenario
product
m3 µg-1
kJ mol-1
α-pinene + OH, low NOx 1
0.307
-0.022
6.98
85.6 2
0.211
0.117
22.2
α-pinene + OH, high NOx 3
0.028
-0.040
0.762
132.2 4
0.109
-0.025
85.3
α-pinene + O3, low NOx 5
0.282
4.155
86.8 6
0.142
0.0158
77.1
α-pinene + O3, high NOx 7
0.016
-0.057
0.837
161.8 8
0.213
111.4
α-pinene + NO3 high NOx 9
0.018
-0.049
0.493
172.4 10
0.251
-0.015
147.6
Reactions

14. 10-product model curves at 298K
More SOA in low-NOx than in high-NOx (factor 8 difference)
α-pinene + OH leads to more SOA than α-pinene + O3

15. Why more SOA in low than high-NOx ?
Hydroperoxides (condensable)
Low-NOx
High-NOx
nitrates
Peroxy acyl nitrates
More decompositions
More volatile products

16. Verification at intermediate NOx
Full model
parameter model
(modified)

17. Sensitivity to photolysis and oxidants
Not accounting for photolysis of SOA during ageing
Accumulation of condensables very high yields
Not very sensitive to chosen OH or HO2

18. Comparison with other parameterizations
Low-NOx :
Yields in this study are higher than for others,
Aging impact
Very low-NO x
But, also high yields in
Ng et al. (2007)
High-NOx :
similar to Presto et al. (2005)
T = 298 K

19. Summary
BOREAM simulations of smog chamber photo-oxidation: most SOA yields within factor 2
Some overestimations for low-NOx
10-product model fit to explicit box model BOREAM including aging
Low-NOx SOA higher than previous parameterizations based on smog chambers (impact aging)
Photolysis of compounds in aerosol phase important
EVAPORATION: New vapour pressure estimation method

20. Thank you for your attention!

21. α-pinene + O3 and pinonaldehyde chemistry