Secondary organic aerosol from low-volatility and traditional VOC precursors

Transcription

1 Secondary organic aerosol from low-volatility and traditional VOC precursors Havala Olson Taylor Pye 1,2 and John H. Seinfeld 1 1 Department of Chemical Engineering, California Institute of Technology 2 Now at US EPA, Atmospheric Modeling and Analysis Division Images: NASA

2 Nontraditional Organic Aerosol IVOCs: Intermediate Volatility Organic Compounds (10 4 < C* < 10 6 μg/m 3 ) Ex: naphthalene, C17 alkanes SVOCs: Semivolatile Organic Compounds (C* < 10 4 ) log 10 (C* [μg/m 3 ])

3 SVOCs vs. IVOCs IVOCs: Intermediate Volatility Organic Compounds (10 4 < C* < 10 6 μg/m 3 ) Ex: naphthalene, C17 alkanes O-SVOC + Ox SOA SOA POA O-IVOC + Ox SVOC IVOC SVOCs: Semivolatile Organic Compounds (C* < 10 4 ) log 10 (C* [μg/m 3 ]) Station fire from Roof Lab, Caltech 2009

4 Emission Rate (Tg/yr) SVOC Emisssions C* 1 = 20 μg/m 3 M O =10 μg/m 3 C* 2 = 1646 μg/m 3 POA log 10 (C* [μg/m 3 ]) SVOC emission 0.51 SVOC SVOC 2 Wood burning parameters from Shrivastava et al ES&T

5 Production Rate (Tg/yr) Gas-phase SVOC Oxidation M O =10 μg/m 3 SVOC 1 + OH O-SVOC 1 SOA + OH + OH SVOC 2 + OH O-SVOC 2 POA log 10 (C* [μg/m 3 ]) Parameter Value Reduction in volatility 100x Increase in mass 50% k OH (cm 3 molec -1 s -1 ) 2x10-11 Number of oxidations 1 Most parameters based on wood burning experiments by Grieshop et al ACP

6 SVOC Global Budget Pie indicates annual net production in TgC (32 TgC total) SVOC and O-SVOC are also wet and dry deposited in gas phase (not shown), all numbers for year 2000

7 IVOC Emissions and Oxidation IVOC emissions Distributed like naphthalene Scaled up to represent all IVOCs IVOC Oxidation IVOC + OH RO 2 RO 2 + HO 2 α 1 P 1 RO 2 + NO α 2 P 2 + α 3 P 3 + Based on naphthalene High yield of nonvolatile SOA under low-no x conditions Semivolatile SOA under high-no x conditions

8 SOA Production from IVOCs

9 Winter OC Concentrations

10 Effect of Parameter Values on DJF OC (relative to traditional simulation) Revised - Traditional Make SVOC Emissions 10x Less Volatile Double IVOC Emissions From Baseline O-SVOC is 1000x Less Volatile than SVOC Double POA Inventory to get SVOC Emissions H-Law is 10 3 M/atm

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12 Updates: SOA from ISOP+NO 3 added Monoterpene and sesquiterpene yield parameters updated to account for NO x Tracers have only one volatility species IVOCs and SVOCs optional

13 Global Net Production of Organic Aerosol (GEOS-Chem 2 x2.5 ) Precursor Traditional POA Semivolatile POA [Tg/yr] [Tg/yr] Terpenes Isoprene Aromatics+IVOCs SVOCs* Oxidized SVOCs Total OA * Non-volatile POA emission rate in Tg/yr for traditional POA simulation

14 Conclusions SVOCs are potentially the largest global source of secondary organic aerosol Significant uncertainty remains regarding their emissions and aging New lumping scheme separates aerosol by volatility (no more soa restart file!) Scheme in GEOS-Chem pipeline to be implemented as an option Acknowledgements: Arthur Chan (UC Berkeley), Mike Barkley (U. Leicester), Joey Ensberg (Caltech) The numerical simulations for this research were performed on Caltech s Division of Geological & Planetary Sciences Dell cluster. For an evaluation of this organic aerosol treatment in CMAQ, see Joey Ensberg s poster References: Pye and Seinfeld: A global perspective on aerosol from low-volatility organic compounds, ACP, Pye et al.: Global modeling of organic aerosol: the importance of reactive nitrogen (NO x and NO 3 ), ACP, 2010.

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16 Primary vs. Secondary Organic Aerosol + Ox VOCs SOA POA

17 Absorptive Partitioning A gas-phase parent HC reacts to form several semi-volatile compounds: HC Ox 1G 1 2 G 2 K ig i G i A i The relative amount in each phase is governed by absorptive partitioning (Pankow, 1994 Atm. Env.): K i M O K i 1 C i * A i RT G i M O o M w i P i i A i other A i aerosol-phase concentration G i gas-phase concentration α i mass-based stoichiometric coefficient M O total aerosol mass for partitioning K i equilibrium partitioning coefficient P o i vapor presure of pure species i at T C i * saturation vapor pressure

18 Partitioning as a Function of C* Fraction of Semivolatile in Aerosol Phase vs. Saturation Vapor Pressure (M o = 10 μg/m 3 ) Fraction in Aerosol A i G i A i log 10 (C* i [μg/m 3 ])

19 POA is semivolatile and oxidation produces more aerosol POA is semivolatile Diesel Exhaust Robinson et al., 2007 Science Two challenges: What is the volatility profile and magnitude of emissions? How do emissions age in the atmosphere?

20 Aerosol from SVOCs

21 Significant Evaporation of SOA on Global Basis

22 SVOCs and IVOCs Have Different C SVOC Emission Fraction Modern C IVOC Emission Fraction Modern C

23 Global Budget Sensitivity Estimated range of global OA production: Tg/yr

24 Biogenic Emissions C 5 H 8 Isoprene Monoterpenes Sesquiterpenes C 10 H 16 C 15 H 24 age LAI Model of Emission of Gases and Aerosol from Nature (MEGAN) (Guenther et al., 2006 ACP): ER age LAI T [ P LDF (1 LDF)] Baseline emission rate Activity factor for age Activity factor for leaf area index T Activity factor for temperature p Activity factor for light LDF Light-dependence fraction

25 Terpene SOA HC Description Aerosol Formation Pathways Experimental Data MTPA Bicyclic monoterpenes + OH,O3; + HO2 + OH,O3; + NO High and Low NOx: a-pinene ozonolysis (Shilling 2008, Ng 2007) + NO3 NO3: b-pinene + NO3 (Griffin 1999) LIMO Limonene + OH,O3; + HO2 + OH,O3; + NO + NO3 High and Low NOx: limonene ozonolysis (Zhang 2006) NO3: b-pinene + NO3 (Griffin 1999) MTPO Other monoterpenes + OH,O3; + HO2 + OH,O3; + NO High and Low NOx: a-pinene ozonolysis (Shilling 2008, Ng 2007) + NO3 NO3: b-pinene + NO3 (Griffin 1999) SESQ Sesquiterpenes + OH,O3; + HO2 + OH,O3; + NO + NO3 High and Low NOx: a-humulene, b- caryophyllene (Griffin 1999, Ng 2007) NO3: b-pinene + NO3 (Griffin 1999) Multiple pathways use VBS to reduce tracers

26 Odum 2-product vs. the VBS Odum 2-product: Volatility basis set (VBS): HC Ox 1P 1 2 P 2 HC Ox 1P 1 2 P 2 3 P 3 4 P 4 Fitted parameters: 1, 2, K 1, K 2 + Minimizes number of tracers per parent HC system (2 gas, 2 aerosol for each system) + Can capture chamber data well - Lumping different systems involves approximation/is not straightforward Fitted parameters: 1, 2, 3, 4 + Can capture chamber data well + Lumping of different systems is more straightforward and can result in less tracers overall - Requires more products for a given parent HC system (usually 4 gas, 4 aerosol) Naphthalene + OH Both methods result in fits that are unconstrained outside the range for which data is available. Odum 2-product 3-product VBS

27 NO x Dependence of Terpene Aerosol Monoterpenes have much higher yields under low-no x conditions (except limonene) Sesquiterpenes have much lower yields under low-no x conditions (data is not at 298 K) Data: Shilling et al., 2008 ACP Data: Griffin et al., 1999 JGR

28 Isoprene SOA Isoprene SOA pathways: ISOP + OH (Kroll et al., 2006 data) ISOP + NO 3 (Ng et al., 2008 data)

29 Minor Effect of NO x -Dependent Aerosol Change in total OA as a result of forcing the parent HC through high-no x or low-no x yields Increased aerosol from monoterpenes and light aromatics Significant isoprene, nitrate radical oxidation, and sesquiterpene aerosol Less aerosol from monoterpenes and light aromatics Plots for August Reference total OA levels are the same as the previous slide (model calculated ).

30 NO x Branching Ratio HC + Ox RO 2 RO 2 + HO 2 α a P 1 + α b P 2 + RO 2 + NO α c P 1 + α d P 2 + Fraction of peroxy radical reacting with NO: k RO2 NO NO k RO2 NO NO k RO 2 HO 2 HO 2 Plots for August 2000

31 Significant Aerosol from NO 3 Oxidation Aerosol from the NO 3 oxidation pathway contributes roughly half of the terpene aerosol (enhancement of 100%) in the Southeast Isoprene + NO 3 aerosol is also significant Total aerosol is enhanced about 30% due to aerosol from NO 3 oxidation Plots for August 2000, Traditional POA

32 Biogenic SOA Important in Summer

33 Contributions to Global OA Fraction of Parent Hydrocarbon Reacting in the Gas Phase Through Each Pathway Contribution of Each Pathway to Aerosol from a Given Parent Hydrocarbon Estimated for M O = 1.5 g/m 3