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

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).

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?

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 v9-01-03 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

Global Distribution of O/C: Standard Model Simulation (June, 2008) Surface O/C ranges from 0.3-0.7 with little seasonal difference. Compared to 2005-2011 Surface O/C data from HR-AMS measurements along with 4 additional Q-AMS data.

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.

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.

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 v9-01-03 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 v9-01-03 gas particle Updated Scheme Volatile Organic Compounds Hydrophilic Primary OA Hydrophobic Gas-phase Products i Secondary OA Standard Model: GEOS-Chem v9-01-03 gas particle

First Look: How Does Global Distribution of O/C Change with Aging? kOH, 1-3 = 1.1 × 10-12 cm3 molec-1 s-1 ~ 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)

First Look: Does Aging Improve Simulation of O/C Compared to Observations? kOH, 1-3 = 1.1 × 10-12 cm3 molec-1 s-1 ~ 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.

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 0.4-0.5. 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