1. Parameterization of Global Monoterpene SOA formation and Water Uptake, Based on a Near-explicit Mechanism
Karl Ceulemans – Jean-François Müller – Steven Compernolle – Jenny Stavrakou
Belgian Institute for Space Aeronomy, Brussels, Belgium
ACM Conference, Davis, 2010

2. Secondary Organic Aerosol modeling
Atmospheric aerosols
SOA in smog chambers
???
Explicit models too large, many model uncertainties
Detailed SOA box models
Parameter models
Aerosol in Global models

3. Do smog chambers represent atmospheric SOA well? Photochemical aging??? =
Atmospheric aerosols
SOA in smog chambers
+OH
Parameter model +
online aging scheme
Parameters from box model simulations
Detailed SOA box models
Aerosol in Global models

4. Outline BOREAM: Near-explicit model for α-pinene SOA
10-product model parameterization including aging
Water uptake
Global modelling

5. 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)

6. 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)

7. Model performance: Photo-oxidation
two low-NOx experiments (Ng et al. 2007)
most SOA yields within factor 2

8. 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 aging
Diurnal cycle for VOC, OH, HO2 and O3 ; deposition
SOA equilibrium after 12 days

9. 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

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

11. 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

12. 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

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

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

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

16. 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

17. Water uptake Parameterizations were obtained for dry conditions
increases molecule number absorbing phase
more condensation organic compounds
Non-ideality effects
Activity coefficients correct for non-ideality

18. Fitted activity coefficients
against BOREAM
, (impact water non-ideality on organic fraction)

19. Impact of water uptake on SOA
Significant increase of SOA due to water
Good agreement between full and parameter model
Constant activity coefficients cause errors at high RH

20. Global Modeling Using global CTM IMAGESv2 (Stavrakou et al. 2009)
Parameter model α-pinene used for SOA from all monoterpenes
Other types of Organic Aerosol:
Isoprene: Henze and Seinfeld (2006)
Sesquiterpenes: Griffin et al.(1999)
Aromatics: Henze et al. (2008)
Small dicarbonyls (cloud processing and aqueous aerosol):
Stavrakou et al. (2009)
POA: non-volatile (Bond et al. 2004, Van der Werf et al )

21. Results U Global SOA production (Tg/year) Monoterpenes 18.8 20.7 8.7
Images No water
ImagesWith
water
Henze
et al.
(2008)
Tsigaridis (2007)
Pye et al. (2010)
Farina
(2010)
Monoterpenes
18.8
20.7
8.7
12.1
13.7
17.2
Sesquiterpenes
8.2
11.0
2.1
3.9
Isoprene
35.6
49.5
14.4
4.6
7.9
6.5
Aromatics
3.8
4.0
3.5
1.8
8.5*
1.6
Dicarbonyls
33.2
34.0
Total SOA
100
119 30 19
30.1
28.9
POA source* 62 70 44
39.2* 81
SOA burden(Tg)
1.75
2.12
0.81
0.82
0.54
Lifetime (days)
6.4
9.8
16.1
6.8

22. Global model results (July 2004)
Total OA (μg m-3)
Total SOA (μg m-3)
Monoterpene SOA (μg m-3)
fraction of total OA (%)

23. Modeled impact of water uptake on surface OA concentratios

24. Results Comparisons with observations: U.S.
too large seasonal variation of OC in Eastern US
MEGAN emissions might be overestimated by a factor of 2 in Eastern US (Warneke et al., 2010; Stavrakou et al., 2010)
water uptake: mostly associated with isoprene SOA, highly uncertain

25. Comparisons with observations (cont.)

26. Summary
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
Global modeling with IMAGESv2
Higher SOA than in most previous studies ( Tg/a)
Monoterpenes : 20 Tg/a
Water uptake significantly increases SOA
Agreement over US: reasonable, but underestimations in winter
Still wide spread in SOA for global models

27. Thank you for your attention!

28. α-pinene + O3 and pinonaldehyde chemistry