lable at ScienceDirect

Atmospheric Environment 95 (2014) 105e112

Contents lists avai

Atmospheric Environment

journal homepage: www.elsevier .com/locate/atmosenv

Aqueous oxidation of green leaf volatiles by hydroxyl radicalas a source of SOA: Kinetics and SOA yields

Nicole K. Richards-Henderson a, Amie K. Hansel b, Kalliat T. Valsaraj b, Cort Anastasio a, *

a Department of Land, Air and Water Resources, University of California e Davis, 1 Shields Ave., Davis, CA 95616, USAb Cain Department of Chemical Engineering, Louisiana State University, South Stadium Road, Baton Rouge, LA 70803, USA

h i g h l i g h t s

* Corresponding author.E-mail address: canastasio@ucdavis.edu (C. Anasta

http://dx.doi.org/10.1016/j.atmosenv.2014.06.0261352-2310/© 2014 Published by Elsevier Ltd.

g r a p h i c a l a b s t r a c t

� We assessed the potential contribu-tion of aqueous GLV reactions as asource of SOA.

� Second-order rate constants for GLVswith OH ranged from (5.4e8.6) � 109 M�1 s�1.

� Aqueous-phase SOA mass yieldsranged from 10 to 88%.

� Calculations show that SOA forma-tion from these GLVs is a minorcontributor to SOA.

a r t i c l e i n f o

Article history:Received 25 January 2014Received in revised form9 June 2014Accepted 12 June 2014Available online 12 June 2014

Keywords:Secondary organic aerosolBiogenic volatile organic compoundsChemical kineticsMultiphase chemistry

a b s t r a c t

Green leaf volatiles (GLVs) are a class of oxygenated hydrocarbons released from vegetation, especiallyduring mechanical stress or damage. The potential for GLVs to form secondary organic aerosol (SOA) viaaqueous-phase reactions is not known. Fog events over vegetation will lead to the uptake of GLVs intowater droplets, followed by aqueous-phase reactions with photooxidants such as the hydroxyl radical(OH). In order to determine if the aqueous oxidation of GLVs by OH can be a significant source of sec-ondary organic aerosol, we studied the partitioning and reaction of five GLVs: cis-3-hexen-1-ol, cis-3-hexenyl acetate, methyl salicylate, methyl jasmonate, and 2-methyl-3-butene-2-ol. For each GLV wemeasured the kinetics of aqueous oxidation by OH, and the corresponding SOA mass yield. The second-order rate constants for GLVs with OH were all near diffusion controlled, (5.4e8.6) � 109 M�1 s�1 at298 K, and showed a small temperature dependence, with an average activation energy of 9.3 kJ mol�1

Aqueous-phase SOA mass yields ranged from 10 to 88%, although some of the smaller values were notstatistically different from zero. Methyl jasmonate was the most effective aqueous-phase SOA precursordue to its larger Henry's law constant and high SOA mass yield (68 ± 8%). While we calculate that theaqueous-phase SOA formation from the five GLVs is a minor source of aqueous-phase SOA, the avail-ability of other GLVs, other oxidants, and interfacial reactions suggest that GLVs overall might be a sig-nificant source of SOA via aqueous reactions.

© 2014 Published by Elsevier Ltd.

sio).

1. Introduction

Atmospheric aerosols impact climate (Kanakidou et al., 2005;Stocker et al., 2013), visibility, and human health (Dockery et al.,1993; Pope and Dockery, 2006). A substantial fraction of atmo-spheric aerosols are organic and secondary (Hallquist et al., 2009;

N.K. Richards-Henderson et al. / Atmospheric Environment 95 (2014) 105e112106

Jimenez et al., 2009). Secondary organic aerosol (SOA) is generallyconsidered to be formed from the gas-phase oxidation of volatileorganic compounds, where semi- or low-volatility products eitherform new particles or condense onto pre-existing particles (Krolland Seinfeld, 2008; Odum et al., 1996; Pankow, 1994b, 1994a;Rudich et al., 2007). More recently, it has been found that SOAcan also form in atmospheric aqueous phases, e.g., in fog and clouddroplets. In the aqueous-phase formation of SOA, gas-phase speciespartition into the aqueous phase, react, and form low volatilitymaterial that remains in the particle phase after the drop evapo-rates (Blando and Turpin, 2000; Ervens et al., 2011).

Biogenic volatile organic compounds (BVOCs) are importantprecursors for the formation of gas-phase SOA in the atmosphere,since they have significant global emission rates and generallygreater reactivity than anthropogenic VOCs (Guenther et al., 1995,2012). Globally, vegetation emits approximately 1.2 � 1015 g C peryear, representing approximately 88% of VOC emissions to the at-mosphere (Guenther et al., 2012). The emission and oxidation ofBVOCs have been studied for decades (Andreae and Crutzen, 1997;Fuentes et al., 2000; Guenther et al., 1995) with a focus on theoxidations of isoprene and mono- and sesquiterpenes due to theirhigh emissions (Guenther et al., 1995; Ortega and Helmig, 2008).However, recent estimates of global SOA formation indicate thatthere may be significant concentrations of unknown SOA pre-cursors in the atmosphere (Goldstein and Galbally, 2007).

One class of oxygenated BVOCs that are emitted by vegetation isthe green leaf volatiles (GLVs) (Arey et al., 1991; K€onig et al., 1995;Winer et al., 1992), which are formed from the biochemical con-version of linoleic and linolenic acid within plant cells (Hatanaka,1993; Matsui, 2006). Compounds in this class consist of low mo-lecular weight alcohols, aldehydes, fatty acids and esters. Mixingratios of GLVs in the atmosphere are typically 100e800 pptv(Jardine et al., 2010; Kim et al., 2010; Williams et al., 2001). Inaddition, GLV emissions can be elevated under a range of stresses,including severe weather, mechanical stress, insects, and patho-gens (Fall et al., 1999; Jardine et al., 2012; Karl et al., 2001; Kleistet al., 2012; Mentel et al., 2013; Pinto et al., 2007).

In the gas phase, GLVs are oxidized by O3 and OH to form lowvolatility products that produce SOA with aerosol mass yields from0.7 to 20% (Hamilton et al., 2009; Harvey et al., 2014; Jaoui et al.,2012; Mentel et al., 2013). GLVs are modestly soluble in waterand possess a range of vapor pressures ranging from semi-volatile(methyl jasmonate (MeJa) and methyl salicylate (MeSa)) to inter-mediate volatility (cis-3-hexen-1-ol (HxO), cis-3-hexenyl acetate(HxAc), and 2-methyl-3-butene-2-ol (MBO); Table 1). Thus thesecompounds might be a source of aqueous-phase SOA, either in bulksolution or at the air-aqueous interface. While many species havebeen examined as a potential source of aqueous-phase SOA (Ervenset al., 2008; Gong et al., 2011; Haan et al., 2009; Huang et al., 2011;

Table 1Properties of the five GLVs studied.a

Compound (abbreviation) Molecularformula

Molecular weight(MA, g mol�1)

Vaporpressure (atm)b

Methyl Jasmonate (MeJa) C13H20O3 224.3 4.3 � 10�7

Methyl salicylate (MeSa) C8H8O3 152.15 7.0 � 10�5

Cis-3-hexen-1-ol (HxO) C6H12O 100.16 1.2 � 10�3

2-Methyl-3-buten-1-ol (MBO) C5H10O 86.1 3.7 � 10�2

Cis-3-hexenyl acetate (HxAc) C8H15O2 142.19 1.5 � 10�2

a Values given at 298 K.b Vapor pressures were estimated using MPBPVP estimation method (EPA, 2010).c Calculated from estimated vapor pressures.d Water solubilities were determined by Kow values estimated using KOWWIN v. 16.8e Rate constants were estimated using the structure estimation method AOPwin (EPAf Vempati et al., in preparation.

Lee et al., 2011; Lim et al., 2013; Liu et al., 2009; McNeill et al., 2012;Ortiz-Montalvo et al., 2012; Sun et al., 2010; Tan et al., 2012; Zhanget al., 2010; Zhou et al., 2011) no studies have evaluated SOA for-mation from aqueous GLV oxidation. To address this we examinedthe bulk aqueous chemistry of five GLVs: HxO, HxAc, MBO, MeJa,and MeSa. For each species we: (1) quantified its aqueous-phasesecond-order rate constant with OH, (2) measured the mass yieldof aqueous SOA from OH oxidation, and (3) assessed its potentialcontribution as a source of aqueous SOA in cloudy or foggy atmo-spheres. In a companion manuscript we examine the mechanismsfor OH oxidation of GLVs to form SOA in the aqueous phase.

2. Experimental

2.1. Chemicals

Cis-3-hexenyl acetate (�98%), cis-3-hexen-1-ol (natural, �98%),2-methyl-3-butene-2-ol (98%), methyl jasmonate (�95%), methylsalicylate (Reagent plus®, �99%), and sodium benzoate (�99.0%,Fluka) were from Sigma Aldrich. Sulfuric acid (trace metal grade,94e98%) and HOOH (30.9%, ACS reagent) were from Fisher. Allchemicals were used as received. Solutions were made using air-saturated purified water from a Milli-Q Plus system (18.2 MU-cm)with an upstream organics cartridge.

2.2. Kinetics experiments

Competition kinetics were performed using sodium benzoate(BA) as the reference compound (Poskrebyshev et al., 2002) todetermine the second-order rate constant for reaction of each GLVwith OH. Solutions were air-saturated and contained one or moreGLVs (50 mM), BA (50 mM), and H2O2 (500e1000 mM) as a photo-chemical source of OH. Solutions were typically at pH 5.4 ± 0.2 (thepH of ourMilli-Q water), but we alsomeasured rate constants at pH3.1 ± 0.1 (adjusted with sulfuric acid) and pH 6.9 ± 0.2 (adjustedwith sodium borate). pH was measured using an Orion pH probe atthe beginning and end of each experiment; during the duration ofthe experiment the pH change was less than ±0.1 pH unit.

Experiments were conducted in 2-cm, far-UV, air-tight quartzcuvettes (Spectrocell), placed in an illumination chamber at acontrolled temperature, and continuously stirred with a magneticstir bar. Solutions were irradiated with 313 nm radiation (tophotolyze HOOH) from a monochromatic illumination systemwitha 1000 W Hg/Xe lamp. For each illumination experiment twocontrol experiments were also conducted: (1) a dark control underidentical conditions (sample composition and temperature) exceptno illumination and (2) a direct photodegradation control withidentical conditions except no HOOH was added.

Saturationconcentration(mg/m3)c

Watersolubility(mM)d

Gas-phase rate constantkGLVþOH (10�11)(cm3 mlc�1 s�1)e

Henry's lawconstant (M atm�1)f

4.1 � 10�3 0.7 7.4 3500 ± 1500.44 12 1.1 38 ± 24.9 160 6.3 160 ± 20130.4 557 5.8 53 ± 58.7 3.4 6.1 3.6 ± 0.2

(EPA, 2010)., 2010).

N.K. Richards-Henderson et al. / Atmospheric Environment 95 (2014) 105e112 107

At measured time intervals during illumination, aliquots ofsample were removed from the quartz cell and the concentrationsof GLVs and BA were measured using high performance liquidchromatography (HPLC). The HPLC system consisted of a ShimadzuSPD-10A UVeVis detector, LC-10AT pump, and 250 � 33 mm, 5 mMbead, BetaBasic-18 column (Thermo Hypersil-Keystone). HPLCconditions are listed in Supporting Table S1. Concentrations of GLVand BA were not measured past their half-lives to minimize theinfluence of secondary chemistry.

The pseudo first-order rate constants for GLV and BA loss weredetermined from the negative of the slopes of plots ofln GLV½ �t=�

GLV½ �0Þ and ln BA½ �t=�

BA½ �0Þ versus illumination time(Fig. 1), with concentrations at times t and zero. Each pseudo first-order rate constant for OH reaction was corrected for other (veryminor) loss pathways, e.g., evaporation or direct photodegradation(jGLV), by subtracting their corresponding pseudo first-order rateconstants. Therewas essentially no loss in the dark, with an averageratio of the pseudo-first-order rate constant in the dark relative toin the light, i.e., k0Dark/k

0GLV, of ~1 � 10�4. In addition, with one

exception, none of the GLVs showed loss due to direct photo-degradation; the exception is MeSa, which had a photolysis rateconstant (jMeSa) of (3 ± 1)� 10�6 s�1, corresponding to a loss of <1%of initial MeSa over the illumination time of a typical OH experi-ment. The lack of direct photodegradation for nearly all of the GLVsis consistent with their molar absorptivities: MeSa has a value of3510 ± 40 M�1 cm�1 at 313 nm, while the other GLVs have negli-gible absorption in this region (Fig. S2 and Table S2). The darkcontrol was not subtracted separately since mechanisms for GLVloss in the dark (e.g., evaporation) will also contribute to the directphotodegradation result. In the dark control the final concentrationof GLV was at most 5% of the initial concentration and on average�2%, which is within the 3% precision of our HPLC system.

Second-order reaction rate constants for GLV oxidation, kGLVþOH,were determined by equation (1) (Finlayson-Pitts and Pitts, 2000):

kGLVþOH ¼ k'GLVk'BA

kBAþOH (1)

where k0BA and k0GLV are measured pseudo first-order rate constantsand kBAþOH is the bimolecular rate constant for BA þ OH. The

Fig. 1. Typical plot of a relative rate experiment for OH reaction with GLVs, here forMeSa (purple diamonds) and MeJa (orange squares) with the reference compound BA(green circles) at 298 K and pH 5.4 ± 0.2. (For interpretation of the references to colourin this figure legend, the reader is referred to the web version of this article.)

pseudo first-order rate constants are equivalent to the bimolecularrate constant (kGLVþOH or kBAþOH) multiplied by the hydroxyl radicalsteady state, [OH], but this concentration term drops out when thepseudo first-order rate constants for BA and GLV are combined. Thereference second-order rate constant (kBAþOH) is known and thuskGLVþOH can be calculated. Reference rate constants for benzoateoxidation by OH as a function of pH and temperature are in Table 2.Errors in GLV rate constants are relative standard errors (RSE),determined from propagating the RSE of the pseudo first-order rateconstants and uncertainties in kBAþOH.

As a test of BA as an OH probe, we conducted a relative rateexperiment in triplicate to determine the rate constant for OH withbenzene at 293 K and pH 5.4. Our measured value,(8.0 ± 0.2) � 109 M�1 s�1 (±1s), is very close to the average of thefive literature values, which is (7.8 ± 0.3) � 109 M�1 s�1 (Bansalet al., 1971; Buxton et al., 1988; Kochany and Bolton, 1992;Michael and Hart, 1970; Neta and Dorfman Leon, 1968).

2.3. Aqueous SOA mass yields

The mass yield of aqueous SOA (YSOA(aq)) was measured fromsolutions containing 100 mM GLV and 500 mM HOOH using the N2-blow down procedure described by Smith et al. (2014). Solutionswere illuminated in a 25-mL, 5-cm, air-tight FUV quartz cell(Spectrocell) at 298 K with simulated sunlight from a 1000 W Xelamp filtered with an AM 1.0 air mass filter (AM1D-3L, Sciencetech)and 295-nm long-pass filter (20CGA-295, Thorlabs). The spectraloutput from this system is in Fig. S1. We illuminated solutions untilapproximately half of the GLV was degraded, then removed 8.0 mLof the illuminated and dark control solutions and transferred eachto a separate, pre-weighed, aluminum foil cup. Each cup was thenblown down to dryness with N2 (Oxygen Service Co., UHP, 99.999%)at room temperature. In addition to the illuminated and dark so-lutions, we also occasionally blew down a Milli-Q water blank.Mass concentrations for the dark and Milli-Q controls were, onaverage (±1s), 1.54 ± 0.92 mgmL�1 (n¼ 25) and 0.95 ± 0.19 mgmL�1

(n ¼ 6), respectively. In comparison, average mass concentrationsfor the illuminated GLV þ HOOH solutions ranged from2.1 ± 0.3 mg mL�1 (for MBO) to 12.6 ± 0.1 mg mL�1 (for MeJa). Oncedry, the samples were weighed and YSOA(aq) was determined:

YSOAðaqÞ ¼ðMass of illuminated sample�Mass of the darkÞ

Mass of GLV reacted(2)

Aluminum cups were heated to 600 �C for 12 h prior to use inYSOA(aq) experiments to remove organic compounds and wereweighed three consecutive times using an electro balance (Cahn,±1 mg) before (no solution added) and after solution blow downs.As a test to examine if YSOA(aq) is sensitive to the extent of GLV loss,an experiment was performed where masses were measured afteronly 25% of MeJa was oxidized by OH; the SOA mass yield waswithin experimental error of the yields determined with 50% loss ofMeJa.

Dissolution of the blown-down material in water and subse-quent analysis by HPLC showed that there were negligible amountsof GLV remaining after blow down, with the exception of MeJa,where ~7% remained in the blown-down material for both theilluminated and dark sample. None of the dark controls showedsubstantial GLV loss during an experiment. Experiments were alsoconducted in the absence of HOOH to determine whether directphotodegradation formed any low-volatility products in the SOAexperiments: there was insignificant GLV loss ranging from�0.02%(for HxAc, HxO, MBO and MeJa) to <5% (for MeSa) in the absence ofHOOH and therefore these controls were not blown down. Each

Table 2Rate constants for the observed aqueous-phase reaction of OH with GLVs and BA at different temperatures and pH values.

Temp., K pHa kGLVþOH (109 M�1 s�1)

MeJa MeSa HxO MBO HxAc BAb

278 5.4 5.2 ± 0.3 6.6 ± 0.3 4.0 ± 0.2 6.1 ± 0.8 6.5 ± 0.5 4.9 ± 0.2283 5.4 5.3 ± 0.3 7.1 ± 0.5 4.6 ± 0.2 6.3 ± 0.4 6.9 ± 0.4 5.2 ± 0.1288 5.4 5.8 ± 0.3 7.5 ± 0.6 4.6 ± 0.2 7.0 ± 0.4 7.0 ± 0.8 5.5 ± 0.1293 5.4 6.4 ± 0.2 7.9 ± 0.5 4.9 ± 0.2 7.4 ± 0.5 8.0 ± 0.6 5.9 ± 0.2298 5.4 6.7 ± 0.3 8.4 ± 0.6 5.3 ± 0.3 8.0 ± 0.6 8.6 ± 0.5 6.2 ± 0.1298 3.1 6.8 ± 0.8 7.8 ± 0.5 5.1 ± 0.8 7.5 ± 1.4 8.7 ± 1.1 4.3 ± 0.8c

298 6.9 6.8 ± 0.5 8.1 ± 0.6 5.3 ± 0.2 7.3 ± 0.7 8.3 ± 0.6 6.3 ± 0.2d

A (1011 M�1 s�1) 5.4 4.0 ± 0.3 2.2 ± 0.8 1.7 ± 0.6 3.7 ± 0.8 4.5 ± 0.7 2.4 ± 0.6b

Ea, kJ mol�1 5.4 9.4 ± 1.5 8.1 ± 1.4 8.6 ± 1.3 9.6 ± 0.9 9.7 ± 1.5 8.8 ± 0.6b

a Error bars on pH units are ± 0.2 (SE).b Rate constants for pH 5.4 solutions were calculated using Eq. (3) and A and Ea from previously published values (Poskrebyshev et al., 2002). Calculated rate constants at 293

and 298 K were within 5% of previously published values (Buxton et al., 1988; Poskrebyshev et al., 2002).c Wander et al., 1968.d Buxton et al., 1988.

N.K. Richards-Henderson et al. / Atmospheric Environment 95 (2014) 105e112108

YSOA(aq) was measured three times for each GLV; errors werecalculated by propagating errors from mass and replicateexperiments.

Fig. 2. Arrhenius plot for the reaction of OH with the five GLVs at a pH of 5.4 ± 0.2.Error bars represent ±1 SE, propagated from the standard errors of k0GLV, jGLV, andkBAþOH.

3. Results and discussion

3.1. Temperature and pH dependence of bimolecular rate constants

As illustrated in Fig. 1, the degradations of GLVs and BA by OHfollow pseudo first-order kinetics, while there is no decay of GLVsor BA in the dark. Using equation (1) with the raw kinetic data (e.g.,Fig. 1), we calculated the second-order rate constants for theoxidation of each GLV by OH. As summarized in Table 1, theobserved bimolecular rate constants are all within a narrow range,(5.4e8.6) � 109 M�1 s�1, close to the diffusion-controlled limit of1010 M�1 s�1 (Buxton et al., 1988). The contribution of diffusion tothe bimolecular rate constants, determined by a method used byseveral groups (Elliot et al., 1990; Gligorovski and Herrmann, 2004;Ziajka and Rudzinski, 2007), is provided in Section S2 of the SI andshows that there is some diffusion limitation to our reactivity rateconstants. Our observed rate constants are within the range ofvalues for small aromatics and structurally similar ketones and al-cohols (Buxton et al., 1988; Ervens et al., 2003). OH oxidation ofalkenes and aromatics typically proceeds via addition at a site ofunsaturation or by abstraction of a hydrogen atom from a carbonatom. Comparing our measured values with calculated values fromstructureeactivity relationships (SAR) by Monod and Doussin(Doussin and Monod, 2013; Monod and Doussin, 2008) shows thatthe calculations work well for three of the GLVs but not for MBO orMeJa (Section S3 of the SI). However, these SAR predictions arebased on H-abstraction mechanisms from saturated hydrocarbons,while the GLVs are unsaturated and aromatic compounds. Asdescribed in our companion paper (Hansel et al., in preparation),OH addition appears to be the main oxidation pathway for MeJaand MeSa.

We also examined the effects of pH and temperature on thesecond-order rate constants for GLV reactions with OH. Rate con-stants are independent of pH (Table 2), as expected since GLVsstudied have no acid-base changes in the range of acidities tested(pH 3e7). Fig. 2 shows the rate of GLV oxidation by OH over a rangeof temperatures (278e298 K) and the results are all fit well(R2 ¼ 0.92e0.98) by the Arrhenius equation:

lnðkGLVþOHÞ ¼ lnðAÞ � Ea=RT (3)

where A is the pre-exponential factor, Ea is the activation energy,and R is the gas constant. This figure shows that the bimolecular

rate constants are only weakly dependent on temperature, withvalues at 278 K only 21e26% lower compared to at 298 K. Theactivation energies for the GLV þ OH reactions are all similar, be-tween 8.1 and 10 kJ mol�1 (Table 2), and are within the range of Eavalues for near diffusion-controlled reactions in water for similarorganic species (8_18 kJ mol�1) (Ervens et al., 2003).

The activation parameters for each reaction, i.e., the activationentropy (DSs), activation enthalpy (DНs) and the free Gibbsenthalpy (DGs) are provided in Table 3 and were calculated fromobserved rate constants corrected by diffusion (discussed in Section2 of the SI). The Gibbs energies of OH-oxidation of GLVs are all in afairly narrow range, from 14.6 kJ mol�1 (for MeSa) to 16.5 kJ mol�1

(for MBO); this suggests that all GLV-OH oxidations have a similartransition state and that the reactions proceed through the samereaction mechanism. The DGs we obtain is lower than the value of~20 kJ mol�1 from previous studies for saturated compounds,where hydrogen abstraction is a key mechanism (Ervens et al.,2003; Liu et al., 2009). The lower DGs for our unsaturated GLVssuggests that OH-oxidation proceeds via addition to the double

Table 3Arrhenius parameters from the corrected observed bimolecular rate constants obtained during GLV-OH oxidation. A ¼ collision parameter, Ea ¼ activation energy,DSs ¼ activation entropy, DНs ¼ activation enthalpy, and DGs ¼ free Gibbs enthalpy.

Activation parameters pH MeJa MeSa HxO MBO HxAc

A (1011 M�1 s�1) 5.4 58 ± 9 58 ± 40 8.1 ± 0.9 23 ± 5 190 ± 40Ea, kJ mol�1 5.4 15 ± 1.5 14 ± 1.4 12 ± 0.3 13 ± 2 17 ± 1.5DSX, J mol�1a 5.4 �8.8 ± �1.7 �8.9 ± �4 �25 ± �1 �16 ± �5.2 �0.93 ± �2DHX, kJ mol�1a 5.4 13 ± 0.6 12 ± 1.8 9.2 ± 0.3 11 ± 2.5 15 ± 2DGX, kJ mol�1a 5.4 16 ± 0.6 15 ± 1.5 17 ± 0.43 16 ± 0.9 16 ± 1.7

a Activation parameters calculated at 298 K, as described in Section S3 in the SI.

N.K. Richards-Henderson et al. / Atmospheric Environment 95 (2014) 105e112 109

bond, in agreement with results from our companion manuscript(Hansel et al., in preparation).

3.2. SOA mass yields

Understanding the contribution of aqueous oxidation of GLVs byOH to SOA also requires that we know the yields of low volatilityproducts from these reactions. To measure the SOA mass yields(YSOA(aq)) we determined themass of low-volatility material formedfrom GLV oxidation using the mass of the blown-down illuminatedsample after subtracting the corresponding mass in the darksample (Eq. (2)). The blow-down mass in the dark range from0.84 mg mL�1 (for MBO) to 1.3 mg mL�1 (for MeJa), representing40%e10% of the corresponding illuminated values. Half-lives of theGLVs in the presence of OH for our YSOA(aq) experiments are 8e10 h;based on our bimolecular rate constants (Table 2), this correspondsto aqueous OH steady-state concentrations of approximately1 � 10�15 M.

As shown in Fig. 3, the GLV aqueous SOA yields fall into twobroad groups: MeJa, MeSa, HxO, which form aqueous SOA effi-ciently (YSOA(aq) ¼ 68, 88, and 50%, respectively), and MBO andHxAc, whose aqueous SOA yields are low (20 and 10%, respec-tively) and not significantly different from zero (p > 0.05). Thelarge uncertainties for MBO and HxAc are due to uncertainties inmass measurements (1e2 mg) and low SOA masses (4e15 mg).However, the error bars shown in Fig. 3 are upper limits: relativestandard deviations from replicate experiments range from 3%(for MeSa) to 30% (for HxAc), while the plotted RSDs of 15% (forMeJa) to 66% (for HxAc) were calculated from propagating errors.

Fig. 3. Comparison of the aqueous-phase SOA mass yields for reaction of the five GLVswith OH at 298 K and pH 5.4 ± 0.2. Error bars are ±1 SE, propagated from the standarderrors from mass measurements for each replicate (n � 3).

Dissolution of the SOA material shows that, on average, only 2% orless of the initial GLV remained after blow down, indicating thatthe GLV SOA is comprised of low-volatility products. The charac-terization of the products in the aqueous SOA fromMeJa and MeSais discussed by the accompanying paper (Hansel et al., inpreparation).

Aqueous-phase SOA yields from the oxidation of organics by OHhave been measured in several previous studies. SOA mass yieldsfor the OH oxidation of aqueous methacrolein and methyl vinylketone are 2e12% and 24%, respectively (El Haddad et al., 2009;Harvey et al., 2014; Zhang et al., 2010), which are similar to ouryield for MBO (20%), which is also a small, unsaturated molecule(although without a carbonyl group). In addition, our YSOA(aq) forMeSa (88 ± 16%), a phenolic BVOC, is similar to values from theaqueous oxidation of phenols by OH or an excited triplet excitedstate, with average values of (90 ± 8)% and (107 ± 12)%, respectively(Anastasio and Sun, in preparation; Smith et al., 2014).

GLVs are also sources of SOA via gas-phase reactions. For theGLVs we studied, values of YSOA(g) for the gas-phase oxidation by OHare 20% (MeSa), 3.1% (HxO), 0.7% (MBO), and 0.93% (HxAc) (Chanet al., 2010; Hamilton et al., 2009; Jaoui et al., 2012; Mentel et al.,2013); as best we can tell, there is no reported value for MeJa. Fora given GLV, our aqueous SOA yield is 5e38 times higher than thegas-phase SOA yield, suggesting the aqueous reactions more effi-ciently form oligomers (Liu et al., 2012; Renard et al., 2013; Smithet al., 2014) and functionalized/oxygenated products, while thegas-phase reactions form more fragmented, higher volatilityproducts.

Hamilton et al. (2009) showed that the SOAmass yields from thegas-phase oxidation of HxO and HxAc by O3 are significantlyinfluenced by the reactivity of the first generation products, whichcan form oligomers and high molecular weight oxygenated prod-ucts. They found that YSOA(g) for HxAc is less than that for HxObecause the acetate group in the former inhibits oligomer forma-tion. We see a similar effect in the aqueous phase via OH oxidation:HxO is 5.6 times more efficient in making SOA than HxAc, sug-gesting the acetate group also inhibits SOA formation in theaqueous phase.

3.3. Significance of aqueous-phase formation of SOA by GLVs

The half-lives of GLVs via oxidation by OH in the gas andaqueous phase are the same order of magnitude (hours). Therefore,the relative importance of the aqueous- and gas-phase reactionpathways depends strongly on the GLV gas-aqueous partitioning(i.e., the Henry's law constant, KH) and the SOA yields in each phase.To examine the relative importance of each phase, we first estimatethe rates of SOA formation from aqueous oxidation of the GLVs byOH. Assuming the ambient gas-phase GLV partial pressures (PGLV)are approximately 5 � 10�10 atm (Jardine et al., 2010; Kim et al.,2010; Williams et al., 2001), and using KH values in Table 1, wecan estimate the equilibrium aqueous-phase concentrations of theGLVs ([GLV(aq)]):

N.K. Richards-Henderson et al. / Atmospheric Environment 95 (2014) 105e112110

GLVðaqÞ ¼ KH � PGLV (4)

h i

Values range from 1.8 � 10�3 mM for HxAc to 1.8 mM for MeJa.Combining these concentrations with YSOA(aq) (Fig. 3), the molec-ular weight of the GLV (MA, Table 1), second-order rate constants at298 K (kGLVþOH, Table 2), and assuming a mid-range [OH] of7.7 � 10�15 M in fog water (Arakaki et al., 2013), we estimate therate of aqueous SOA formation (RSOA(aq)) using:

RSOAðaqÞ ¼ kGLVþOH

hOHðaqÞ

ihGLVðaqÞ

iMA YSOAðaqÞ (5)

As shown in Fig. 4, MeJa has, by far, the largest rate of aqueousSOA formation of the five GLVs from OH oxidation. This is primarilybecause its KH value is 22e980 times higher than the values for theother GLVs, which are smaller than 103 M atm�1 (Table 1), theapproximate threshold for significant formation of aqueous SOA(Gelencser and Varga, 2005). As a result, the rate of aqueous SOAformation from OH reactionwith MeJa is 100 times higher than thecombined rate from the other four GLVs (Table S7). Combining therates from the five GLVs, assuming a 12-h period of light, andmultiplying by a liquid water content of 1 �10�7 L-aq/L-air, revealsthat the total rate of aqueous SOA formation via OH reaction is only0.06 mg m�3-air.

We next estimate the gas-phase rates of SOA generation asdescribed in Section S5 of the Supporting Information. Over a 12-hperiod, the calculated gas-phase amount of SOA formed by OH fromthe four GLVs with published SOA yields is 0.9 mg m�3, which is 15times higher than the aqueous-phase amount. Though gas-phaseSOA mass yields are 5e38 times lower than aqueous-phaseyields, GLVs will primarily remain in the gas phase due to theirlow KH values, resulting in the majority of SOA being formed in thegas phase rather than the aqueous phase. In order for aqueous-phase formation of SOA to be an important source relative to thegas-phase, KH would have to be on the order of 1 � 104 M atm�1

which would require enhancements by factors of 3 (for MeJa) to3000 (for HxAc) over the measured values in water. Studies haveshown that KH can be enhanced by increasing ionic strength(Kampf et al., 2013) and organic concentration (Healy et al., 2008;van Pinxteren et al., 2005) and these enhancements can be up toa factor of 104. Therefore, these effects could enhance KH to the

Fig. 4. Calculated rates of aqueous-phase formation of SOA from the five GLVs reactingwith OH at 298 K and pH 5.4 ± 0.2. Error bars are propagated from errors in kGLVþOH,YSOA(aq), and KH.

magnitude needed for aqueous-phase GLV-OH reactions to beimportant pathways for SOA formation.

4. Conclusions

All of the GLVs rapidly react with OH in the aqueous phase (withrate constants � 4 � 109 L mol�1 s�1) and three of the GLVs (MeJa,MeSa and HxO) efficiently make aqueous SOA, with mass yields of50% or greater. However, due to small Henry's law constants, mostof the GLVs partition weakly to the aqueous phase and thus makenegligible amounts of aqueous SOA. The one exception is MeJa,which has a Henry's law constant of 3500 M atm�1 and can make amodest amount of aqueous SOA.

However, there are four reasons that GLVs as a class might bemore significant than these results suggest. First, we only studiedfive GLVs, but dozens have been identified in the atmosphere (Fallet al., 1999), some with acidic functional groups, e.g., salicylic andjasmonic acids, and large values of KH (�1 � 105 M atm�1) (EPA,2010). Second, other oxidants present in fog water, such as ozone,singlet molecular oxygen (Anastasio and McGregor, 2001) andexcited triplet states of organic photosensitizers (Canonica et al.,2000, 1995) might be significant in aqueous SOA formation fromGLVs. Third, although many of the GLV KH values are small(<1�103 M�1 atm�1), recent molecular dynamic simulations showthat MBO and MeSa can react with OH at the airewater interface(Liyana-Arachchi et al., 2013a, 2013b), suggesting that heteroge-neous processes at the airewater interface might be an importantpathway for SOA from GLVs and other surface-active organics.Finally, concentrations of GLVs can be elevated by as much as afactor of ten due to mechanical and weather induced stress (Karlet al., 2001), which would increase the aqueous concentration ofGLVs and their formation of aqueous SOA (as well as their gas-phase SOA). Together, these unknowns indicate that the potentialfor GLVs to form aqueous SOA might be considerably higher thanestimated here.

Acknowledgements

This researchwas supported by the National Science Foundation(Grant AGS-1106569) with additional support from the CaliforniaAgricultural Experiment Station (Project CA-D*-LAW-6403-RR).The authors thank Jeremy D. Smith, Dr. Franz S. Ehrenhauser, RichieKaur, and the anonymous reviewers for insightful comments, DerekBau and Tobias Kraft for laboratory assistance, Kathryn George forcombusting the aluminium cups, and Dr. Ann Dillner for use of anelectro balance.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.atmosenv.2014.06.026.

References

Anastasio, C., McGregor, K.G., 2001. Chemistry of fog waters in California's CentralValley: 1. In situ photoformation of hydroxyl radical and singlet molecularoxygen. Atmos. Environ. 35, 1079e1089.

Anastasio, C., Sun, J.,2014 (in preparation).Andreae, M.O., Crutzen, P.J., 1997. Atmospheric aerosols: biogeochemical sources

and role in atmospheric chemistry. Science 276, 1052e1058.Arakaki, T., Anastasio, C., Kuroki, Y., Nakajima, H., Okada, K., Kotani, Y., Handa, D.,

Azechi, S., Kimura, T., Tsuhako, A., Miyagi, Y., 2013. A general scavenging rateconstant for reaction of hydroxyl radical with organic carbon in atmosphericwaters. Environ. Sci. Technol. 47, 8196e8203.

Arey, J., Winer, A.M., Atkinson, R., Aschmann, S.M., Long, W.D., Lynn Morrison, C.,1991. The emission of (Z)-3-hexen-1-ol, (Z)-3-hexenylacetate and otheroxygenated hydrocarbons from agricultural plant species. Atmos. Environ 25,1063e1075.

N.K. Richards-Henderson et al. / Atmospheric Environment 95 (2014) 105e112 111

Bansal, K.M., Patterson, L.K., Fendler, E.J., Fendler, J.H., 1971. Reactions of hydratedelectrons, hydrogen atoms and hydroxyl radicals in micellar systems. Int. J.Radiat. Appl. Instrum. C. Radiat. Phys. Chem. 3, 321e331.

Blando, J.D., Turpin, B.J., 2000. Secondary organic aerosol formation in cloud and fogdroplets: a literature evaluation of plausibility. Atmos. Environ. 34, 1623e1632.

Buxton, G.V., Greenstock, C.L., Helman, W.P., Ross, A.B., 1988. Critical review of rateconstants for reactions of hydrated electrons, hydrogen atoms and hydroxylradicals (OH/O�) in aqueous solution. J. Phys. Chem. Ref. 17, 513e886.

Canonica, S., Hellrung, B., Wirz, J., 2000. Oxidation of phenols by triplet aromaticketones in aqueous solution. J. Phys. Chem. A 104, 1226e1232.

Canonica, S., Jans, U., Stemmler, K., Hoigne, J., 1995. Transformation kinetics ofphenols in water: photosensitization by dissolved natural organic material andaromatic ketones. Environ. Sci. Technol. 29, 1822e1831.

Chan, A.W.H., Chan, M.N., Surratt, J.D., Chhabra, P.S., Loza, C.L., Crounse, J.D.,Yee, L.D., Flagan, R.C., Seinfeld, J.H., 2010. Role of aldehyde chemistry and NOxconcentrations in secondary organic aerosol formation. Atmos. Chem. Phys. 10,7169e7188.

Dockery, D.W., Pope, C.A., Xu, X., Spengler, J.D., Ware, J.H., Fay, M.E., Ferris, B.G.,Speizer, F.E., 1993. An association between air pollution and mortality in six U.S.cities. N Engl. J. Med. 329, 1753e1759.

Doussin, J.F., Monod, A., 2013. Structureeactivity relationship for the estimation ofOH-oxidation rate constants of carbonyl compounds in the aqueous phase.Atmos. Chem. Phys. 13, 11625e11641.

El Haddad, I., Yao, L., Nieto-Gligorovski, L., Michaud, V., Temime-Roussel, B.,Quivet, E., Marchand, N., Sellegri, K., Monod, A., 2009. In-cloud processes ofmethacrolein under simulated conditions e part 2: formation of secondaryorganic aerosol. Atmos. Chem. Phys. 9, 5107e5117.

Elliot, A.J., McCracken, D.R., Buxton, G.V., Wood, N.D., 1990. Estimation of rateconstants for near-diffusion-controlled reactions in water at high temperatures.J. Chem. Soc. Faraday Trans. 86, 1539e1547.

EPA, U.S., 2010. Estimation Program Interface (EPI) Suite. Ver. 4.1. Available as of Mar13, 2013.

Ervens, B., Carlton, A.G., Turpin, B.J., Altieri, K.E., Kreidenweis, S.M., Feingold, G.,2008. Secondary organic aerosol yields from cloud-processing of isopreneoxidation products. Geo. Res. Lett. 35, L02816.

Ervens, B., Gligorovski, S., Herrmann, H., 2003. Temperature-dependent rate con-stants for hydroxyl radical reactions with organic compounds in aqueous so-lutions. Phys. Chem. Chem. Phys. 5, 1811e1824.

Ervens, B., Turpin, B.J., Weber, R.J., 2011. Secondary organic aerosol formation incloud droplets and aqueous particles (aqSOA): a review of laboratory, field andmodel studies. Atmos. Chem. Phys. 11, 11069e11102.

Fall, R., Karl, T., Hansel, A., Jordan, A., Lindinger, W., 1999. Volatile organic com-pounds emitted after leaf wounding: on-line analysis by proton-transfer-reaction mass spectrometry. J. Geophys. Res. 104, 15963e15974.

Finlayson-Pitts, B.J., Pitts, J.N., 2000. Chemistry of the Upper and Lower Atmosphere.Academic Press, New York.

Fuentes, J.D., Lerdau, M., Atkinson, R., Baldocchi, D., Bottenheim, J., Ciccioli, P.,Lamb, B., Geron, C., Gu, L., Guenther, A.B., Sharkey, T., Stockwell, W., 2000.Biogenic hydrocarbons in the atmospheric boundary layer: a review. Bull. Amer.Meteor. Soc. 81, 1537e1575.

Gelencser, Varga, 2005. Evaluation of the atmospheric significance of multiphasereactions in atmospheric secondary organic aerosol formation. Atmos. Chem.Phys. 5, 2823e2831.

Gligorovski, S., Herrmann, H., 2004. Kinetics of reactions of OH with organiccarbonyl compounds in aqueous solution. Phys. Chem. Chem. Phys. 6,4118e4126.

Goldstein, A.H., Galbally, I.E., 2007. Known and unexplored organic constituents inthe earth's atmosphere. Environ. Sci. Technol., 1515e1521.

Gong, W., Stroud, C., Zhang, L., 2011. Cloud processing of gases and aerosols in airquality modeling. Atmosphere 2, 567e616.

Guenther, A., Hewitt, C.N., Erickson, D., Fall, R., Geron, C., Graedel, T., Harley, P.,Klinger, L., Lerdau, M., McKay, W.A., Pierce, T., Scholes, B., Steinbrecher, R.,Tallamraju, R., Taylor, J., Zimmerman, P., 1995. A global model of natural volatileorganic compound emissions. J. Geophys. Res. 100, 8873e8892.

Guenther, A.B., Jiang, X., Heald, C.L., Sakulyanontvittaya, T., Duhl, T., Emmons, L.K.,Wang, X., 2012. The model of emissions of gases and aerosols from natureversion 2.1 (MEGAN2.1): an extended and updated framework for modelingbiogenic emissions. Geosci. Model Dev. 5, 1471e1492.

Haan, D.O.D., Corrigan, A.L., Smith, K.W., Stroik, D.R., Turley, J.J., Lee, F.E.,Tolbert, M.A., Jimenez, J.L., Cordova, K.E., Ferrell, G.R., 2009. Secondary organicaerosol-forming reactions of glyoxal with amino acids. Environ. Sci. Technol. 43,2818e2824.

Hallquist, M., Wenger, J.C., Baltensperger, U., Rudich, Y., Simpson, D., Claeys, M.,Dommen, J., Donahue, N.M., George, C., Goldstein, A.H., Hamilton, J.F.,Herrmann, H., Hoffmann, T., Iinuma, Y., Jang, M., Jenkin, M.E., Jimenez, J.L.,Kiendler-Scharr, A., Maenhaut, W., McFiggans, G., Mentel, T.F., Monod, A.,Prevot, A.S.H., Seinfeld, J.H., Surratt, J.D., Szmigielski, R., Wildt, J., 2009. Theformation, properties and impact of secondary organic aerosol: current andemerging issues. Atmos. Chem. Phys. 9, 5155e5236.

Hamilton, J.F., Lewis, A.C., Carey, T.J., Wenger, J.C., Borras i Garcia, E., Munoz, A.,2009. Reactive oxidation products promote secondary organic aerosol forma-tion from green leaf volatiles. Atmos. Chem. Phys. 9, 3815e3823.

Hansel, A.K., Ehrenhauser, F.S., Richards-Henderson, N.K., Valsaraj, K.T.,Anastasio, C., 2014. Aqueous Phase Oxidation of Green Leaf Volatile Compoundsas a Source of Secondary Organic Aerosol: Product Identification for Methyl

Jasmonate and Methyl Salicylate Oxidation by Hydroxyl Radical (inpreparation).

Harvey, R.M., Zahardis, J., Petrucci, G.A., 2014. Establishing the contribution of lawnmowing to atmospheric aerosol levels in American suburbs. Atmos. Chem. Phys.14, 797e812.

Hatanaka, A., 1993. The biogeneration of green odour by green leaves. Phyto-chemistry 34, 1201e1218.

Healy, R.M., Wenger, J.C., Metzger, A., Duplissy, J., Kalberer, M., Dommen, J., 2008.Gas/particle partitioning of carbonyls in the photooxidation of isoprene and1,3,5-trimethylbenzene. Atmos. Chem. Phys. 8, 3215e3230.

Huang, D., Zhang, X., Chen, Z.M., Zhao, Y., Shen, X.L., 2011. The kinetics andmechanism of an aqueous phase isoprene reaction with hydroxyl radical.Atmos. Chem. Phys. 11, 7399e7415.

Jaoui, M., Kleindienst, T.E., Offenberg, J.H., Lewandowski, M., Lonneman, W.A., 2012.SOA formation from the atmospheric oxidation of 2-methyl-3-buten-2-ol andits implications for PM2.5. Atmos. Chem. Phys. 12, 2173e2188.

Jardine, K., Abrell, L., Kurc, S.A., Huxman, T., Ortega, J., Guenther, A., 2010. Volatileorganic compound emissions from Larrea tridentata (creosotebush). Atmos.Chem. Phys. 10, 12191e12206.

Jardine, K., Barron-Gafford, G.A., Norman, J.P., Abrell, L., Monson, R.K., Meyers, K.T.,Pavao-Zuckerman, M., Dontsova, K., Kleist, E., Werner, C., Huxman, T.E., 2012.Green leaf volatiles and oxygenated metabolite emission bursts from mesquitebranches following lightedark transitions. Photosynth. Res. 113, 321e333.

Jimenez, J.L., Canagaratna, M.R., Donahue, N.M., Prevot, A.S.H., Zhang, Q., Kroll, J.H.,DeCarlo, P.F., Allan, J.D., Coe, H., Ng, N.L., Aiken, A.C., Docherty, K.S., Ulbrich, I.M.,Grieshop, A.P., Robinson, A.L., Duplissy, J., Smith, J.D., Wilson, K.R., Lanz, V.A.,Hueglin, C., Sun, Y.L., Tian, J., Laaksonen, A., Raatikainen, T., Rautiainen, J.,Vaattovaara, P., Ehn, M., Kulmala, M., Tomlinson, J.M., Collins, D.R., Cubison, M.J.,Dunlea, E.J., Huffman, J.A., Onasch, T.B., Alfarra, M.R., Williams, P.I., Bower, K.,Kondo, Y., Schneider, J., Drewnick, F., Borrmann, S., Weimer, S., Demerjian, K.,Salcedo, D., Cottrell, L., Griffin, R., Takami, A., Miyoshi, T., Hatakeyama, S.,Shimono, A., Sun, J.Y., Zhang, Y.M., Dzepina, K., Kimmel, J.R., Sueper, D.,Jayne, J.T., Herndon, S.C., Trimborn, A.M., Williams, L.R., Wood, E.C.,Middlebrook, A.M., Kolb, C.E., Baltensperger, U., Worsnop, D.R., 2009. Evolutionof organic aerosols in the atmosphere. Science 326, 1525e1529.

Kampf, C.J., Waxman, E.M., Slowik, J.G., Dommen, J., Pfaffenberger, L., Praplan, A.P.,Pr�evot, A.S.H., Baltensperger, U., Hoffmann, T., Volkamer, R., 2013. EffectiveHenry's law partitioning and the salting constant of glyoxal in aerosols con-taining sulfate. Environ. Sci. Technol. 47, 4236e4244.

Kanakidou, M., Seinfeld, J.H., Pandis, S.N., Barnes, I., Dentener, F.J., Facchini, M.C.,Van Dingenen, R., Ervens, B., Nenes, A., Nielsen, C.J., Swietlicki, E., Putaud, J.P.,Balkanski, Y., Fuzzi, S., Horth, J., Moortgat, G.K., Winterhalter, R., Myhre, C.E.L.,Tsigaridis, K., Vignati, E., Stephanou, E.G., Wilson, J., 2005. Organic aerosol andglobal climate modelling: a review. Atmos. Chem. Phys. 5, 1053e1123.

Karl, T., Fall, R., Crutzen, P.J., Jordan, A., Lindinger, W., 2001. High concentrations ofreactive biogenic VOCs at a high altitude site in late autumn. Geo. Res. Lett. 28,507e510.

Kim, S., Karl, T., Guenther, A., Tyndall, G., Orlando, J., Harley, P., Rasmussen, R.,Apel, E., 2010. Emissions and ambient distributions of biogenic volatile organiccompounds (BVOC) in a ponderosa pine ecosystem: interpretation of PTR-MSmass spectra. Atmos. Chem. Phys. 10, 1759e1771.

Kleist, E., Mentel, T.F., Andres, S., Bohne, A., Folkers, A., Kiendler-Scharr, A.,Rudich, Y., Springer, M., Tillmann, R., Wildt, J., 2012. Irreversible impacts of heaton the emissions of monoterpenes, sesquiterpenes, phenolic BVOC and greenleaf volatiles from several tree species. Biogeosciences 9, 5111e5123.

Kochany, J., Bolton, J.R., 1992. Mechanism of photodegradation of aqueous organicpollutants. 2. Measurement of the primary rate constants for reaction of hy-droxyl radicals with benzene and some halobenzenes using an EPR spin-trapping method following the photolysis of hydrogen peroxide. Environ. Sci.Technol. 26, 262e265.

K€onig, G., Brunda, M., Puxbaum, H., Hewitt, C.N., Duckham, S.C., Rudolph, J., 1995.Relative contribution of oxygenated hydrocarbons to the total biogenic VOCemissions of selected mid-European agricultural and natural plant species.Atmos. Environ. 29, 861e874.

Kroll, J.H., Seinfeld, J.H., 2008. Chemistry of secondary organic aerosol: formationand evolution of low-volatility organics in the atmosphere. Atmos. Environ. 42,3593e3624.

Lee, A.K.Y., Herckes, P., Leaitch, W.R., Macdonald, A.M., Abbatt, J.P.D., 2011. AqueousOH oxidation of ambient organic aerosol and cloud water organics: formation ofhighly oxidized products. Geo. Res. Lett. 38, L11805.

Lim, Y.B., Tan, Y., Turpin, B.J., 2013. Chemical insights, explicit chemistry and yieldsof secondary organic aerosol from methylglyoxal and glyoxal. Atmos. Chem.Phys. 13, 8651e8667.

Liu, Y., El Haddad, I., Scarfogliero, M., Nieto-Gligorovski, L., Temime-Roussel, B.,Quivet, E., Marchand, N., Picquet-Varrault, B., Monod, A., 2009. In-cloud pro-cesses of methacrolein under simulated conditions part 1: aqueous phasephotooxidation. Atmos. Chem. Phys. 9, 5093e5105.

Liu, Y., Siekmann, F., Renard, P., El Zein, A., Salque, G., El Haddad, I., Temime-Roussel, B., Voisin, D., Thissen, R., Monod, A., 2012. Oligomer and SOA formationthrough aqueous phase photooxidation of methacrolein and methyl vinyl ke-tone. Atmos. Environ. 49, 123e129.

Liyana-Arachchi, T.P., Hansel, A.K., Stevens, C., Ehrenhauser, F., Valsaraj, K.T.,Hung, F.R., 2013a. Molecular modeling of the green leaf volatile methylsalicylate on atmospheric air/water interfaces. J. Phys. Chem. A 117,4436e4443.

N.K. Richards-Henderson et al. / Atmospheric Environment 95 (2014) 105e112112

Liyana-Arachchi, T.P., Stevens, C., Hansel, A.K., Ehrenhauser, F.S., Valsaraj, K.T.,Hung, F.R., 2013b. Molecular simulations of green leaf volatiles and atmosphericoxidants on air/water interfaces. Phys. Chem. Chem. Phys. 15, 3583e3592.

Matsui, K., 2006. Green leaf volatiles: hydroperoxide lyase pathway of oxylipinmetabolism. Curr. Opin. Plant Biol. 9, 274e280.

McNeill, V.F., Woo, J.L., Kim, D.D., Schwier, A.N., Wannell, N.J., Sumner, A.J.,Barakat, J.M., 2012. Aqueous-phase secondary organic aerosol and organo-sulfate formation in atmospheric aerosols: a modeling study. Environ. Sci.Technol. 46, 8075e8081.

Mentel, T.F., Kleist, E., Andres, S., Maso, M.D., Hohaus, T., Kiendler-Scharr, A.,Rudich, Y., Springer, M., Tillmann, R., Uerlings, R., Wahner, A., Wildt, J., 2013.Secondary aerosol formation from stress-induced biogenic emissions andpossible climate feedbacks. Atmos. Chem. Phys. 13, 8755e8770.

Michael, B.D., Hart, E.J., 1970. Rate constants of hydrated electron, hydrogen atom,and hydroxyl radical reactions with benzene, 1,3-cyclohexadiene, 1,4-cyclo-hexadiene, and cyclohexene. J. Phys. Chem. 74, 2878e2884.

Monod, A., Doussin, J.F., 2008. Structure-activity relationship for the estimation ofOH-oxidation rate constants of aliphatic organic compounds in the aqueousphase: alkanes, alcohols, organic acids and bases. Atmos. Environ. 42,7611e7622.

Neta, P., Dorfman Leon, M., 1968. Pulse Radiolysis Studies. XIII. Rate Constants forthe Reaction of Hydroxyl Radicals with Aromatic Compounds in Aqueous So-lutions, Radiation Chemistry. American Chemical Society, pp. 222e230.

Odum, J.R., Hoffmann, T., Bowman, F., Collins, D., Flagan, R.C., Seinfeld, J.H., 1996.Gas/particle partitioning and secondary organic aerosol yields. Environ. Sci.Technol. 30, 2580e2585.

Ortega, J., Helmig, D., 2008. Approaches for quantifying reactive and low-volatilitybiogenic organic compound emissions by vegetation enclosure techniques epart A. Chemosphere 72, 343e364.

Ortiz-Montalvo, D.L., Lim, Y.B., Perri, M.J., Seitzinger, S.P., Turpin, B.J., 2012. Volatilityand yield of glycolaldehyde SOA formed through aqueous photochemistry anddroplet evaporation. Aero. Sci. Technol. 46.

Pankow, J.F., 1994a. An absorption model of gas/particle partitioning of organiccompounds in the atmosphere. Atmos. Environ. 28, 189e193.

Pankow, J.F., 1994b. An absorption model of gas/particle partitioning of organiccompounds in the atmosphere. Atmos. Environ. 28, 185e188.

Pinto, D., Nerg, A.-M., Holopainen, J., 2007. The role of ozone-reactive compounds,terpenes, and green leaf volatiles (GLVs), in the orientation of Cotesia plutellae.J. Chem. Ecol. 33, 2218e2228.

Pope, C.A., Dockery, D.W., 2006. Health effects of fine particulate air pollution: linesthat connect. J. Air Waste Manag. Assoc. 56, 709e742.

Poskrebyshev, G.A., Neta, P., Huie, R.E., 2002. Temperature dependence of the aciddissociation constant of the hydroxyl radical. J. Phys. Chem. A 106, 11488e11491.

Renard, P., Siekmann, F., Gandolfo, A., Socorro, J., Salque, G., Ravier, S., Quivet, E.,Cl�ement, J.L., Traikia, M., Delort, A.M., Voisin, D., Vuitton, V., Thissen, R.,

Monod, A., 2013. Radical mechanisms of methyl vinyl ketone oligomerizationthrough aqueous phase OH-oxidation: on the paradoxical role of dissolvedmolecular oxygen. Atmos. Chem. Phys. 13, 6473e6491.

Rudich, Y., Donahue, N.M., Mentel, T.F., 2007. Aging of organic aerosol: bridging thegap between laboratory and field studies. Annu. Rev. Phys. Chem. 58, 321e352.

Smith, J., Sio, V., Yu, L., Zhang, Q., Anastasio, C., 2014. Secondary organic aerosolproduction from aqueous reactions of atmospheric phenols with an organictriplet excited state. Environ. Sci. Technol. 48, 1049e1057.

Stocker, T.F., Qin, D., Plattner, G.-K., Tignor, M., Allen, S.K., Boschung, J., Nauels, A.,Xia, Y., Bex, V., Midgley, P.M., 2013. IPCC, 2013: Climate Change 2013: ThePhysical Science Basis. Contribution of working group I to the fourth assessmentreport of the intergovernmental panel on climate change. Cambridge UniversityPress, Cambridge, United Kingdom and New York, NY, USA.

Sun, Y.L., Zhang, Q., Anastasio, C., Sun, J., 2010. Insights into secondary organicaerosol formed via aqueous-phase reactions of phenolic compounds based onhigh resolution mass spectrometry. Atmos. Chem. Phys. 10, 4809e4822.

Tan, Y., Lim, Y.B., Altieri, K.E., Seitzinger, S.P., Turpin, B.J., 2012. Mechanisms leadingto oligomers and SOA through aqueous photooxidation: insights from OHradical oxidation of acetic acid and methylglyoxal. Atmos. Chem. Phys. 12,801e813.

van Pinxteren, D., Plewka, A., Hofmann, D., Müller, K., Kramberger, H., Svrcina, B.,B€achmann, K., Jaeschke, W., Mertes, S., Collett Jr., J.L., Herrmann, H., 2005.Schmücke hill cap cloud and valley stations aerosol characterisation duringFEBUKO (II): organic compounds. Atmos. Environ. 39, 4305e4320.

Wander, R., Neta, P., Dorfman, L.M., 1968. Pulse radiolysis studies. XII. Kinetics andspectra of the cyclohexadienyl radicals in aqueous benzoic acid solution. J. Phys.Chem. 72, 2946e2949.

Williams, J., P€oschl, U., Crutzen, P.J., Hansel, A., Holzinger, R., Warneke, C.,Lindinger, W., Lelieveld, J., 2001. An atmospheric chemistry interpretation ofmass scans obtained from a proton transfer mass spectrometer flown over thetropical rainforest of Surinam. J. Atmos. Chem. 38, 133e166.

Winer, A.M., Arey, J., Atkinson, R., Aschmann, S.M., Long, W.D., Morrison, C.L.,Olszyk, D.M., 1992. Emission rates of organics from vegetation in California'scentral valley. Atmos. Environ. 26, 2647e2659.

Zhang, X., Chen, Z.M., Zhao, Y., 2010. Laboratory simulation for the aqueous OH-oxidation of methyl vinyl ketone and methacrolein: significance to the in-cloud SOA production. Atmos. Chem. Phys. 10, 9551e9561.

Zhou, Y., Zhang, H., Parikh, H.M., Chen, E.H., Rattanavaraha, W., Rosen, E.P.,Wang, W., Kamens, R.M., 2011. Secondary organic aerosol formation from xy-lenes and mixtures of toluene and xylenes in an atmospheric urban hydro-carbon mixture: water and particle seed effects (II). Atmos. Environ. 45,3882e3890.

Ziajka, J., Rudzinski, K.J., 2007. Autoxidation of SIV inhibited by chlorophenolsreacting with sulfate radicals. Environ. Chem. 4, 355e363.