1. Simulating the Oxygen Content of Organic Aerosol in a Global Model
Qi Chen, Colette L. Heald
Department of Civil and Environmental Engineering,
Massachusetts Institute of Technology
AGU Fall Meeting (A52E-06), Dec 7, 2012
Funded by NSF

2. Atmospheric Organic Particles
dry or wet deposition
NR-PM1 chemical composition
(Heald et al., ACP, 2011)
(Spracklen et al., ACP, 2011)
Models substantially underestimate the observed concentrations of organic aerosol (OA).

3. Global Modeling of OA: Additional Sources?
Aqueous-phase secondary organic aerosol (SOA) production
Spracklen et al. (2011) suggests that an additional source of 100 Tg yr-1 anthropogenically controlled SOA can close the measurement-model gap. Mechanism unclear.
Atmospheric aging is not included in the model, which may increase the OA mass.
(Jimenez et al., Science, 2009)
Hydrocarbon-like OA
Semi-volatile oxygenated OA
Low-volatility oxygenated OA
Can O/C be a useful constraint on the global budget of OA?

4. Simulating O/C: Applying Experimental Data to Model
Absorptive Partitioning Model
α - stoichiometric mass yield
C*- saturation concentration
Volatile Organic Compounds
Hydrophilic
Primary OA
Hydrophobic
Gas-phase Products i
Secondary OA
Standard Model:
GEOS-Chem v
gas
particle
Example of 2-product fitting of yield and elemental composition: α-pinene dark ozonolysis, low NOx ; other SOA systems are also parameterized in this project.
Adding another dimension of input parameters:
Input O/Ci ranges from 0.2 to 0.9

5. Global Distribution of O/C: Standard Model Simulation
(June, 2008)
Surface O/C ranges from with little seasonal difference.
Compared to Surface O/C data from HR-AMS measurements along with 4 additional Q-AMS data.

6. How Does the Standard Model Simulation Compare to Observations?
Standard model simulations reproduce the observations of O/C in near-source regions but underestimate the values in aged locations.

7. Does the Addition of 100 Tg/yr Anthropogenically-controlled SOA Source Improve the Comparison?
Addition of anthropogenic SOA leads increased O/C at all locations but has little skill on the spatial variability.

8. Simulating O/C: Adding a Simple Scheme for Oxidative Aging of OA
Volatile Organic Compounds
Hydrophilic
Primary OA
Hydrophobic
Primary OA:
Anthropogenic
Biofuel
Biomass Burning
Gas-phase Products i
Secondary OA
Standard Model:
GEOS-Chem v
gas
particle
Aged OA
kOH, 2
kOH, 3
kOH, 1
Elemental ratios and apparent rate constants are constrained by literature values (Turpin and Lim, EST, 2001; Aiken et al., EST, 2008; Mohr et al., EST, 2009; Lambe et al., ACP, 2011)
Updated Scheme
Volatile Organic Compounds
Hydrophilic
Primary OA
Hydrophobic
Primary OA:
Anthropogenic
Biofuel
Biomass Burning
Gas-phase Products i
Secondary OA
Standard Model:
GEOS-Chem v
gas
particle
Updated Scheme
Volatile Organic Compounds
Hydrophilic
Primary OA
Hydrophobic
Gas-phase Products i
Secondary OA
Standard Model:
GEOS-Chem v
gas
particle

9. First Look: How Does Global Distribution of O/C Change with Aging?
kOH, 1-3 = 1.1 × cm3 molec-1 s ~ 7 days exposure (Lambe et al., 2011)
Standard Simulation
0.43 ± 0.05 for 60˚S to 60˚N
Surface OA in aged environment is dominated by POA.
Simulation with Aging
0.66 ± 0.09 for 60˚S to 60˚N
Surface OA in aged environment is dominated by Aged OA and POA.
(June, 2008)

10. First Look: Does Aging Improve Simulation of O/C Compared to Observations?
kOH, 1-3 = 1.1 × cm3 molec-1 s ~ 7 days exposure (Lambe et al., 2011)
The simplified aging scheme shows the potential to improve model simulation at aged locations. On-going project: sensitivity study on input parameters (e.g., kOH) and model resolution.

11. Summary
We applied experimental constraints on O/C simulated with the global GEOC-Chem model.
The model simulations are compared to recent surface measurements by HR-AMS. The standard simulation reproduces the observed O/C values in near-source regions. However, the model has little skill in aged locations and underestimates O:C by
We developed a simple model scheme to simulate aging based on recent laboratory observations. Preliminary model simulations with POA and SOA aging show model improvements of O/C at some aged locations. On- going…
Acknowledgements
Data sharing from Jose Jimenez Group (CU); Qi Zhang Group (UC Davis);
Ling-Yan He, Xiao-Feng Huang (PKU, China); Manjula Canagaratna, Douglas Worsnop (Aerodyne); Niall Robinson, Hugh Coe (U. Manchester)
NSF for funding