Secondary Organic Aerosol Produced from Aqueous Reactions of Phenols

1. Secondary Organic Aerosol Produced from Aqueous Reactions of Phenols Jeremy D. Smith1; Lu Yu2; Kathryn George3; Haley Kinney1; Travis C. Ruthenburg3; Ann M. Dillner3; Qi Zhang2; CortAnastasio1 1. Department of Land, Air, and Water Resources; 2. Department of Environmental Toxicology; 3. Crocker Nuclear Laboratory University of California, Davis

2. Biomass Burning • Our interest: SOA formation from aqueous reactions of phenols from biomass burning (BB) • BB is a major source of: • Primary organic particles • Water-soluble VOCs (e.g., phenols; KH > 103 M atm-1) • Light-absorbing organic molecules, which can become oxidants • Major sources of BB phenols • Residential wood combustion • Wildfires • Globally BB contributes 33 Tg carbon per year1 1Bond et al., JGR; 2004 Palmbeachpost.com

3. Wood Burning Composition Phenol (PhOH) Guaiacol (GUA) Syringol (SYR) Catechol (CAT) Resorcinol (RES) Hydroquinone (HQ) Benzene Diols 3,4-dimethoxy- benzaldehyde (DMB) Vanillin (Van) Syringaldehyde (SyrAld) Lignin Fragment Phenolic Carbonyls Rogge et al., ES&T, 1998; Hawthorne et al., ES&T 1989; Schauer et al., ES&T, 2001

4. Phenol Reactivity Classes • Most phenols do not absorb sunlight • Phenols (PhOH) • Guaiacols (GUA) • Syringols (SYR) • Benzene diols • Rxns will proceed via oxidants (e.g., •OH) • Phenolic carbonyls and non-phenolic carbonyls absorb sunlight very strongly • Can undergo direct photodegradation • And can react with oxidants • Form excited triplet state (3C*) that can react with phenols Actinic Flux: NCARTUV Model, Zenith Angle = 620

5. * * SOA SOA Non-phenol Chromophore Wood Smoke Emission with higher Relative Humidity Fresh Wood Smoke Emission with low Relative Humidity Droplet Evaporates as RH decreases

6. Project Goals • How fast are phenols oxidized in the aqueous phase by organic triplet excited states (3C*) and hydroxyl radical (•OH)? • How efficiently is aqueous SOA formed from 3C* and •OH? • Will also show some SOA structural and elemental information • Estimate rates of SOA formation from phenols in Central Valley fog impacted by wood combustion • How does the aqueous phase compare to the gas phase? • Five Classes of Phenols: Phenols (PhOH), Guaiacols (GUA), ----Syringols (SYR), Benzene-diols, and Phenolic carbonyls • Note: We will use the abbreviation ‘ArOH’ to refer to all phenols

7. Kinetic Methods • Solutions • Air-saturated, bulk solutions: both illuminated and dark control • Use 5-100 μM phenols (concentrations expected for areas with BB) • Oxidants • Hydroxyl radical (•OH) generated from photolysis of 100 μM HOOH • Excited triplet state (3C*) of DMB (5 μM) • Illumination • Simulated sunlight from filtered 1000 W Xe lamp • Temperature = 20 °C; stirred constantly • Measure photon flux with 2-nitrobenzaldehyde actinometry • Analysis • Monitor concentrations of phenolics and DMB with UV-HPLC • Rate constants for decay are normalized to Davis winter solstice sunlight

8. Results: PhOH + 3C* • Conditions: 10 μM PhOH, 5 μM DMB (3C* precursor), pH 2 • Major points • Dark: No loss of PhOH or DMB • Light: Loss of PhOH, not DMB • Same behavior seen for GUA and SYR with DMB • Oxidant is DMB triplet state, 3C* • OH and 1O2* are insignificant • Data treatment • Determine pseudo-first-order rate constant for ArOH loss: • RArOH = kArOH+3C*[ArOH][3C*] • RArOH = k’ArOH[ArOH] • k’ArOH = kArOH+3C*[3C*] Slope = -k’ArOH

9. 3C* Oxidation Parameters • Major Points: • Protonated triplet is more reactive • Our 3C* possesses acid/base behavior (pKA = 3.3) • Using the relationship: k’ArOH = kArOH+3C* [3C*] we can construct a model mechanism for these reactions • 2nd order rate constant for all of our phenol reactivity classes (kArOH+3C* ): • pH 2: 2.0 – 6.7 109 M-1 s-1 • pH 5: 0.079 – 3.5 109 M-1 s-1 • Diffusion controlled limits of reaction Fog and Cloud water pH pH 2 pH 5 Smith et al., ES&T, 2014

10. SOA Mass Yields • SOA mass yields (YSOA = ΔSOA / ΔArOH) • 100 μM ArOH + 5 μM DMB (or 100 μM HOOH) + light • Illuminate until approx half of ArOH has reacted • Blow down illuminated and dark solutions to dryness; measure masses • YSOA = (illuminated mass – dark mass) / mass of ArOH reacted • YSOA range from 60 – 120% • Average for all conditions: 91% • Values of 3C* and •OH are generally very similar • What does the low-volatility mass look like?

11. Characteristics of Phenol SOA • Products consist of: • Oligomers of the parent phenol • Highly oxygenated monomers • Ring opening products • SOA has much higher oxygen to carbon ratio (O/C) compared to starting phenols • Oxygen incorporation into the SOA Yu et al., 2014, In preparation

12. Atmospheric Implications • First-order rate constants, k’ = k(ArOH + oxidant)[oxidant] • Aq-phase oxidants: [•OH] = 7.5 × 10-15 M,1 [O3]= 6 × 10-10 M • [3C*]= steady-state of triplet excited state of aromatic carbonyls from wood combustion; use 5 µM 3,4-dimethoxybenzaldehyde as model • •OH and O3 rate constants were taken from the literature,23C* and direct photodegradation values were taken from our work (pH 4) • Ozonolysis is only important for benzene diols • 3C* can compete with •OH for the oxidation of phenols in an area heavily impacted by biomass burning • Direct photolysis is only a significant pathway for the phenolic carbonyls t (hr) - 0.5 - 1 - 2 1Arakaki et al., ES&T 2013 2 Buxton et al., J. Phys Chem Ref Data 1988

13. SOA Formation Rates • Using data from heavy biomass burning in Bakersfield, CA from Jan 4-6 19951, we can estimate aqueous concentrations of each phenol classes • Calculated Primary Organic Aerosol Mass : 13.8 µg m-3 • Concentrations are based on Henry’s Law constants and atmospheric conditions (T = 5oC, Liquid water content = 1 × 10–7 L-aq L-1-g) • The Rate of aqueous SOA formation can be estimated by: • RSOA,aq =faqΣ(k’ArOHYSOA))[ArOH(aq,tot)] • Aqueous Phase • Total Rate = 4.0 µg m-3 hr-1 • 3C* path: 1.6 µg m-3 hr-1 • •OH path: 0.9 µg m-3 hr-1 • Direct hv: 1.2 µg m-3hr-1 • Gas Phase • Total Rate = 0.6 µg m-3 hr-1 1Schauer and Cass, ES&T 2000

14. Summary • The oxidation of phenols and benzene-diols by triplet excited states occurs rapidly and can compete with •OH • These reactions produce low-volatility products very efficiently with mass yields near 100% relative to the amount of phenol reacted • In a foggy atmosphere, simple calculations indicate aqueous reactions are more important than gas-phase sources • High rates of SOA formation • Direct photodegradation of aqueous phenolic carbonyls major source • Triplet reactions in aqueous phase are also a major source • Need to check these estimations in a more complex numerical model • Smith, J. D., Sio, V., Yu, L., Zhang, Q., Anastasio, C., Secondary Organic Aerosol Production from Aqueous Reactions of Atmospheric Phenols with an Organic Triplet Excited State, ES&T; 2014, 48, pp 1049-1057.

15. Acknowledgements • Anastasio Research Group • Agricultural and Environmental Chemistry Graduate Group Funding Sources: • National Science Foundation (Grant Number AGS-1036675) • University of California Toxic Substances Research and Teaching Program (TSR&TP) through the Atmospheric Aerosols and Health (AAH) Lead Campus Program • California Agricultural Experiment Station (Project CA-D*-LAW-6403-RR) Contact Information: Cort Anastasio – canastasio@ucdavis.edu Jeremy Smith – jdsmit@ucdavis.edu

16. Questions?

17. Extra Slides

18. Lamp Photon Output

19. Phenol +•OH Oxidation • Conditions: 100 µM ArOH, pH 5, 100 µM HOOH added as a •OH precursor • Major Points: • DARK: No decay of ArOH decay (not shown) • LIGHT: 1st order loss of ArOH • Relative Rate Approach: • Compare the loss of a known compound from • OH oxidation to our phenols • kAROH+•OH values: • pH 2: (1.8-14) ×109 M-1 s-1 • pH 5: (5.8-18) ×109 M-1 s-1

20. Gas – Aqueous Comparison [OH]aq = 7.5  10-7 M [OH]gas = 1  106mlc cm-3 T = 5oC Liquid water Content (LWC) = 1  10-7Laq/ L g