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Simulating the Elemental Ratios (O/C and H/C) of Organic Aerosol by GEOS- Chem

Simulating the Elemental Ratios (O/C and H/C) of Organic Aerosol by GEOS- Chem. Qi Chen, Colette L. Heald 6th International GEOS- Chem User’s Meeting, May 6, 2013 Funded by NSF

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Simulating the Elemental Ratios (O/C and H/C) of Organic Aerosol by GEOS- Chem

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  1. Simulating the Elemental Ratios (O/C and H/C) of Organic Aerosol by GEOS-Chem Qi Chen, Colette L. Heald 6th International GEOS-Chem User’s Meeting, May 6, 2013 Funded by NSF Data sharing from ManjulaCanagaratna, Douglas Worsnop (Aerodyne); Jose Jimenez Group (CU); Qi Zhang Group (UC Davis); Ling-Yan He, Xiao-Feng Huang (PKU, China); Niall Robinson, Hugh Coe (U. Manchester); Scot Martin Group (Harvard).

  2. Motivation • Models substantially underestimated the observed concentrations of organic aerosol (OA), suggesting underrepresented sources/processing. • Elemental ratios can be useful metrics for constraining the OA budget. • When linked to the physical properties of OA (e.g., κ, ρ)  Climate models! Evolution Marker Source Marker fresh aged (Ng et al., 2011) (Nakao et al., 2013; Kuwata et al., 2012; Chen et al., 2011;Chhabra et al., 2010; Bateman et al., 2009; Mohr et al., 2009; Aiken et al., 2008)

  3. Simulating O/C and H/C: Can aging help the model? • Determine O/C and H/C for OAi • 2-product parameterization for SOAi • Various POA sources • O/Ci= 0.2-0.9 • H/Ci = 1.1-1.9 GEOS-Chem (v9-01-03) Standard model with updated yields Volatile Organic Compound i Updated scheme with aging Gas-phase Products gas • Define Aging • Oxidative conversion of carbon mass • fresh OCi+ OH → Aged OCi • Constrain inputs by flow-tube results • O/CAged OA = 1.1 • H/CAged OA = 1.1 • kOH=1 × 10-12 molecule‑1 cm3 s-1 particle Hydrophobic Primary OAi Anthropogenic Biofuel Biomass Burning Hydrophilic Primary OAi Secondary More volatile OAi Less volatile OAi kOH Aged OAi (Ref: Lambe et al., 2011; Nakao et al., 2013; Kuwata et al., 2012; Chen et al., 2011; Chhabra et al., 2010; Bateman et al., 2009; Mohr et al., 2009; Aiken et al., 2008; Turpin and Lim, 2001.)

  4. Can GEOS-Chem capture the observed vertical variability? O/C H/C • Standard model cannot reproduce both magnitude and variations in vertical profiles. • Including aging largely improved the model simulations. • Coarse grid scale model cannot reproduce concentrated plumes.

  5. Global Perspective on Surface O/C (2008) Standard Model Model w/. Aging The aging scheme led a dramatic change in the global picture of O/C and a better capturing the dynamic range of ambient observations from source to remote. H/C shows similar features.

  6. Can GEOS-Chemreproduce the surface elemental ratios? O/C H/C Standard Model Model w/. Aging • Standard model cannot reproduce the ambient ranges of O/C and H/C, and also significantly underestimated O/C, especially for some remote locations. • Including aging significantly improved the model simulations. It can also lead an average increase of 45% in OA mass loading.

  7. Summary Total OA 73% fresh H/C Observations aged aircraft O/C • The oxidative aging scheme developed based on flow-tube studies significantly improved model simulations of O/C and H/C, highlighting the importance of aging in modifying OA composition. • With aging, the estimated global OA burden increased by 73% due to the addition of oxygen  not yet close the gap in OA concentrations (i.e., a factor of 2-10). • Future work: other possible sources.

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