Oligomer and Highly Oxygenated Organic Molecule Formation from Oxidation of Oxygenated Monoterpenes Emitted by California Sage Plants

Home , Eucalyptol

Atmos. Chem. Phys., 20, 10953–10965, 2020 https://doi.org/10.5194/acp-20-10953-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.

Oligomer and highly oxygenated organic molecule formation from oxidation of oxygenated monoterpenes emitted by California sage plants

Archit Mehra1, Jordan E. Krechmer2, Andrew Lambe2, Chinmoy Sarkar3, Leah Williams2, Farzaneh Khalaj4, Alex Guenther3, John Jayne2, Hugh Coe1, Douglas Worsnop2, Celia Faiola4,5, and Manjula Canagaratna2 1Centre for Atmospheric Science, School of Earth and Environmental Sciences, The University of Manchester, Manchester, UK 2Center for Aerosol and Cloud Chemistry, Aerodyne Research Inc., Billerica, Massachusetts, USA 3Department of Earth System Science, University of California Irvine, Irvine, California, USA 4Department of Ecology and Evolutionary Biology, University of California, Irvine, Irvine, California, USA 5Department of Chemistry, University of California, Irvine, Irvine, California, USA

Correspondence: Manjula Canagaratna ([email protected]) and Hugh Coe ([email protected])

Received: 21 March 2020 – Discussion started: 14 April 2020 Revised: 21 July 2020 – Accepted: 7 August 2020 – Published: 24 September 2020

Abstract. Plants emit a diverse range of biogenic volatile or- SOA from oxygenated monoterpenes showed a higher- ganic compounds (BVOCs) whose oxidation leads to sec- order oligomer content and a greater presence of highly ondary organic aerosol (SOA) formation. The majority of oxygenated organic molecules (HOMs) than non-oxygenated studies of biogenic SOA have focused on single or simple monoterpenes, with HOM contributing 27 %–47 % and multicomponent BVOC mixtures thought to be representa- 12 %–14 % of SOA product signal from oxygenated and non- tive of Northern hemispheric deciduous or mixed forest con- oxygenated monoterpenes respectively. This study highlights ditions. Gaps remain in our understanding of SOA formation the potential importance of oxygenated monoterpene emis- from complex mixtures of real plant emissions in other envi- sions for SOA formation in woody shrub ecosystems. ronments. Towards the goal of understanding SOA in other regions, we conducted the first comprehensive study of SOA from 1 Introduction oxygenated monoterpenes. These are the dominant emissions from the most common plant species in southern Califor- Secondary organic aerosol (SOA) formed from the oxidation nia’s coastal sage ecosystem: black sage (Salvia mellifera) of volatile organic compounds (VOCs) contributes 50 %– and California sagebrush (Artemisia californica). 85 % of organic aerosol in the atmosphere (Jimenez et al., Emissions from sage plants, as well as single com- 2009). VOCs from biogenic emission sources (BVOCs) are pounds representing their major emissions (camphor, cam- estimated to contribute 75 %–90 % of the total VOCs (Guen- phene and eucalyptol), were oxidised in an Aerodyne po- ther et al., 1995; Lamarque et al., 2010, Carlton et al., 2009; tential aerosol mass oxidation flow reactor (PAM-OFR). Claeys et al., 2004). BVOC oxidation by reaction with ozone, The chemical composition of SOA was characterised us- hydroxyl radical or nitrate radical has been estimated to con- ing a high-resolution time-of-flight iodide-anion chemical- tribute up to 50 % of SOA worldwide (Chung and Seinfeld, ionisation mass spectrometer equipped with a Filter Inlet for 2002; Hoffmann et al., 1997) with implications for air qual- Gases and AEROsols (FIGAERO-I-HR-ToF-CIMS) under ity, climate and human health (Chung and Seinfeld, 2002; low- and medium-NOx conditions. Fiore et al., 2012; Forster et al., 2007; Lohmann and Feichter, 2005).

Published by Copernicus Publications on behalf of the European Geosciences Union. 10954 A. Mehra et al.: Oligomer and HOM formation from oxidation of oxygenated monoterpenes

The formation of highly oxygenated organic molecules The impact of mixing BVOCs on SOA has been recently (HOMs) has been identified as a pathway for new particle studied using mixtures of α-pinene and isoprene, and results formation (NPF) and growth of SOA (Bianchi et al., 2019; have shown that isoprene can suppress the mass yield derived Ehn et al., 2014). Recent work has shown that alongside from monoterpenes through oxidant scavenging (McFiggans HOM formation from ozonolysis (Quéléver et al., 2019), hy- et al., 2019). Utilisation of detailed chemical composition en- droxyl radical oxidation of monoterpenes is a large source of abled attribution of this effect to a reduction in the yield of HOMs (Berndt et al., 2016). Oligomerisation is another key low-volatility HOM products which form SOA, relative to pathway to formation of SOA and has been identified as im- their yields during single-VOC oxidation (McFiggans et al., portant for monoterpenes including α-pinene and limonene 2019). This study demonstrates the utility of a detailed chem- (Hall and Johnston, 2011; Kourtchev et al., 2016; Kundu et ical composition for the deconvolution of SOA from complex al., 2012; Putman et al., 2011; Tolocka et al., 2004). Un- mixtures. Despite these findings, studies to date have lacked certainties remain in the relative importance and sensitivity an adequate characterisation of differences in the chemical to anthropogenic conditions of the different SOA formation composition between SOA from plants and single precursors. pathways alongside their relevance in other BVOC systems. Relative proportions of different BVOCs in the atmo- Isoprene and α-pinene are globally the most abundant sphere are a function of both the plant species and envi- aerosol-forming BVOCs emitted from vegetation and forests ronmental factors. Thus, VOC mixtures vary regionally and and, thus, have been the focus of many studies on SOA for- globally, making the need to understand SOA formation from mation and composition (Carlton et al., 2009; Després et al., different precursors and mixtures vital for application in re- 2012; Guenther et al., 2012; Kroll, 2006; Zhang et al., 2015). gions with different BVOC source profiles (Guenther, 2013). However, these are only a subset of over 1700 BVOCs that For example, oxygenated monoterpene emissions and am- have been identified from plant emissions (Dudareva et al., bient concentrations were higher than anthropogenic and 2006). Although most of these are thought to have a negli- monoterpene VOCs in some agricultural locations in Cali- gible contribution on the global scale, they could be a major fornia (Gentner et al., 2014), suggesting that they may be contributor in specific ecosystems and, therefore, important important for SOA formation in this region. on local scales. Despite this diversity, the chemical composi- In this study we investigate the VOC emission profile of tion of SOA from the majority of these BVOCs remains un- two species of plant native to California – black sage (Salvia known. Real plant emissions are mixtures of many BVOCs, mellifera, referred to as “Sage” hereinafter) and California yet it remains unclear if the compounds currently used as sagebrush (Artemisia californica, referred to as “Artemisia” proxies for BVOCs are adequate to describe the SOA chem- hereinafter) – and subsequent SOA formation from hydroxyl istry of plants globally (Faiola et al., 2018). radical oxidation of these VOCs in an oxidation flow reactor Real plant emissions have been used as atmospherically (OFR) under low- and medium-NOx conditions. On the basis relevant VOC mixtures in various studies (Faiola et al., 2015, of the measured emission profiles of these species, we also 2019; Hao et al., 2009, 2011; Joutsensaari et al., 2005, 2015; studied SOA formed from individual VOCs that were major Mentel et al., 2009; VanReken et al., 2006; Yli-Pirilä et al., contributors, including camphene, camphor and eucalyptol 2016; Ylisirniö et al., 2020; Zhao et al., 2017); however, (Table 1). most of these studies used conifers or broad-leaved trees. Although terpenoid emissions of sage plants into the at- Comparison of pine species has shown that thresholds of mosphere were reported in the mid-1970s (Tyson et al., 1974) NPF from plant emissions are lower than that for α-pinene and have been considered by plant scientists for their ecologi- alone, and plants with a larger proportion of oxygenated cal function (Karban et al., 2014), this study provides the first VOCs (OVOCs) have the lowest thresholds (Mentel et al., detailed SOA composition measurements from these plants 2009). For mainly isoprene-emitting plants, SOA yields from and is the first study of woody shrubs, which are the dom- co-emitted VOCs were lower than expected from single- inant vegetation type in many landscapes including coastal VOC data, suggesting that isoprene inhibits SOA formation sage scrub, shrub lands and chaparral. Atmospherically rel- (Wyche et al., 2014). Furthermore, the recent incorporation evant studies of the VOC precursors alone have focused on of terpene complexity into a box model has demonstrated gas-phase reaction rates and chemistry but have not looked enhancements of 1.5–2.3 in SOA mass yields from Scots into the SOA (Ceacero-Vega et al., 2012; Gaona-Colmán et pine, relative to the commonly used model monoterpene α- al., 2017). Our results show high HOM and oligomer for- pinene (Faiola et al., 2018). Although studies of SOA from mation from oxygenated monoterpenes, which dominate the real plant emissions are limited, all results show pronounced emission profile of California sage plants. differences between plants and single components. This sug- gests that the simplification of BVOC complexity may be re- sponsible for model underestimates of organic aerosol mass loadings in dry shrubland areas of the western United States (Carlton et al., 2018).

Atmos. Chem. Phys., 20, 10953–10965, 2020 https://doi.org/10.5194/acp-20-10953-2020 A. Mehra et al.: Oligomer and HOM formation from oxidation of oxygenated monoterpenes 10955

Table 1. Volatile organic compounds investigated in this study.

Precursor Formula Structure kOH (cm3 molec.−1 s−1) −11 Camphene C10H16 5.95 × 10 (Gaona-Colmán et al., 2017)

−12 Camphor C10H16O 3.8 × 10 (Ceacero-Vega et al., 2012)

−11 Eucalyptol C10H18O 1.11 × 10 (1,8-cineole) (Corchnoy and Atkinson, 1990)

2 Experimental methods background concentrations (< 0.5 µg m−3), as measured by a scanning mobility particle sizer (SMPS) and an aerosol mass 2.1 Oxidation of VOCs and SOA production spectrometer (AMS). Instrument and OFR backgrounds were determined using N2+O2 injection with lights off and on and SOA particles were generated by the OH oxidation of VOCs with and without precursor injection. The results presented in an Aerodyne potential aerosol mass (PAM) oxidation here are for low-NOx ([NO] < 0.1 ppb) and medium-NOx flow reactor (OFR) (Lambe et al., 2011), affording short ex- ([NO] > 1 ppb, [NO] : [HO2] = 0.5) conditions. perimental timescales and the ability to generate consistent and reproducible oxidation conditions. Plant emissions were 2.2 FIGAERO-I-HR-ToF-CIMS Measurements sampled from an external plant chamber into the OFR using an eductor. The plant enclosure was constructed from Teflon A time-of-flight chemical ionisation mass spectrometer (Lee sheets and was approximately 114 cm × 35 cm × 35 cm. Eu- et al., 2014) using an iodide-anion ionisation system was calyptol was injected into the OFR through a length of Teflon coupled with a Filter Inlet for Gases and AEROsols (FI- tubing using a syringe pump, prior to evaporation into N2 GAERO) (Lopez-Hilfiker et al., 2014) for detection of both carrier gas. Camphene or camphor vapour was introduced gas- and particle-phase composition (referred to as I-CIMS by flowing N2 over solid camphene or camphor placed in hereinafter). The gas-phase inlet consisted of a piece of 0.5 m a Teflon tube. In the OFR, OH, HO2 and NO were generated long 1/400 o.d. (outer diameter) PFA (perfluoroalkoxy) tub- via the following reactions: ing from which the I-CIMS subsampled 2 slpm. The aerosol- phase inlet consisted of 0.5 m stainless-steel tube through O + hv → O(1D) + O (R1) 3 254 2 which 2 slpm was pulled over a Teflon filter. The sample 1 O( D) + H2O → 2OH (R2) flow (gas or aerosol) entered an ion molecule reaction re- 1 gion (IMR) which was maintained at a pressure of 100 mbar O( D) + N2O → 2NO (R3) using a pump fitted with a pressure controller. I− reagent All experiments were carried out at room temperature (ap- ion was made by flowing N2 over a permeation tube con- ◦ proximately 26 C), a relative humidity of 35 % and a containing methyl iodide (CH3I), mixing that flow with a hu- stant gas flow of 10 slpm (standard litres per minute) through midified N2 flow from a bubbler and then ionising with a the OFR, including the injection of ∼ 3 % N2O at the inlet Po-210 (polonium-210) source. Particle mass concentrations to generate NO in a subset of experiments (Lambe et al., were monitored using a TSI scanning mobility particle sizer 2017; Peng et al., 2018). The OFR was run in OFR254 mode (SMPS, TSI, Model 3080), and the collection time on the FI- which uses 254 nm photons to generate radicals by the reac- GAERO filter was varied to ensure hundreds of nanograms tions outlined above, and the estimated OH exposures under of aerosol in each sample for the different precursors. The these conditions are outlined in 2.5. In experiments where FIGAERO thermal desorption cycle consisted of a 15 min ◦ N2O was added to the OFR, the NO/HO2 ratio was approx- temperature ramp to 200 C, a hold at that temperature for imately 0.5, as calculated using an adapted version of the 10 min and then cooling down over 15 min. OFR photochemical box model described in Li et al. (2015) Data analysis is performed using the Tofware package and Peng et al. (2015). Between experiments, the flow reactor (version 3.1.0) running in the Igor Pro (WaveMetrics, OR, was flushed with humidified synthetic air at full lamp power USA) environment. Time-of-flight values were converted to for 12–36 h until the particle mass generated was reduced to mass-to-charge ratios in the I-CIMS data using a calibration https://doi.org/10.5194/acp-20-10953-2020 Atmos. Chem. Phys., 20, 10953–10965, 2020 10956 A. Mehra et al.: Oligomer and HOM formation from oxidation of oxygenated monoterpenes

− − − curve based on the times for I ,I.H2O and I3 . The in- no. C2-AXXX-5149). Sampling lines were conditioned for strument was operated at a ∼ 4000 ThTh−1 resolving power. a minimum of 10 min to minimise VOC line losses before Further analysis was carried out in custom Python 3 proce- attaching adsorbent cartridges. Air was pulled through dupli- dures using the pandas, Matplotlib and NumPy packages. cate cartridges with a sampling pump at 300 cm3 min−1 for While the FIGAERO is capable of providing information 20 min. On days when experiments were run using real plant about both gas and particle phases, the gas-phase I-CIMS emissions, duplicate cartridges were collected at the PAM in- spectra obtained during the medium-NOx experiments were let at least twice per day. Cartridges were shipped overnight complicated by the presence of high nitric acid formed in the to University of California, Irvine on ice for offline analysis OFR from the N2O precursor (Lambe et al., 2017; Peng et al., on a thermal-desorption gas chromatograph interfaced with 2018). High nitric acid depletes the I− reagent ion to form a flame ionisation detector and a time-of-flight mass spec- − NO3 , which subsequently acts as an additional reagent ion trometer (TD-GC-ToF-MS: TD-Series 2 UNITY + ULTRA, and complicates interpretation of the observed CIMS spectra. Markes International; 7890B Agilent GC-FID; BenchTOF- Thus, the gas-phase measurements are deemed unsuitable for Select MS, Markes International). Compounds were identi- the comparison of medium- and low-NOx conditions, and the fied using the 70 eV MS spectra by comparing them with high-resolution analysis of the I-CIMS spectra was only car- compounds in the National Institute of Standards and Tech- ried out for the particle-phase FIGAERO data. These data nology (NIST) library. Terpene mixing ratios at the PAM provide thermal desorption profiles that have been previously inlet were quantified with the FID signal as described else- used to draw conclusions about the volatility distribution of where using the effective carbon-number concept (Faiola et ions. However, we do not make use of this in this study owing al., 2012). to the additional complexity associated with the calibration of the volatility and uncertainties with thermal decomposi- 2.4 AMS measurements tion (Bannan et al., 2019; Schobesberger et al., 2018; Stark et al., 2017); instead, we integrate these desorption profiles SOA composition was continuously measured at the PAM in order to compare the overall composition of the different outlet with a high-resolution long-time-of-flight aerosol mass precursors. For all plant and VOC experiments, > 70 % of spectrometer (HR-LToF-AMS; Aerodyne Research, Inc.), observed product signal was assigned with molecular formu- which is described in detail elsewhere (Canagaratna et al., lae, and these ions are used for analysis in the following. 2007; DeCarlo et al., 2006). Briefly, the HR-LToF-AMS col- Quantification of highly oxidised species measured by I- limates submicron particles into a narrow beam with an aero- CIMS is challenging due to the lack of available standards for dynamic lens. The particle beam is directed onto a vapor- many of the observed products. Previous attempts at quan- iser plate at 600 ◦C to vaporise non-refractory components. tification have used functional group dependencies, collision Volatilised fragments are ionised with 70 eV electron im- limit sensitivities or sensitivities derived from ion-adduct pact ionisation and detected with a long-ToF mass spectrom- declustering scans (Lopez-Hilfiker et al., 2016). Experimen- eter (Tofwerk, resolving power 4000 ThTh−1) where the tal limitations exist in the use of these techniques, meaning ionised fragments are separated by mass. The detection effi- that quantification remains a challenge (Riva et al., 2019); ciency was calibrated with monodisperse ammonium nitrate thus, in this study, we utilise observed ion signal intensities particles generated with a constant output atomiser (TSI, without accounting for species-dependent differences in in- Model 3076) and a differential mobility analyser (DMA, TSI, strument sensitivity. Iodide is more sensitive to oxidised or- Model 3080). AMS data were analysed using the Squirrel ganic species and, thus, is likely to overestimate the relative (v1.60P) and Pika (v1.20P) ToF-AMS toolkits in Igor Pro contribution of the more oxidised compounds and underesti- (v6.37; WaveMetrics, Inc.). Medium-NOx experiments had mate the relative contribution of the less oxidised compounds a large N2O interference with CO2; thus, O/C values are not to SOA. However, given that the comparison here is between presented. VOC and oxidant systems that yield similar products, we expect that these sensitivity differences will not influence 2.5 Summary of experiments the relative contributions of different compounds classes, although estimates of absolute contributions may be an upper During this study, the VOC mixing ratios were measured for bound. the plant mixture experiments by TD-GC-FID–ToF-MS and ranged from 27 to 34 ppb (as shown in Table 2), with approx- 2.3 TD-GC-FID–ToF-MS VOC measurements imately 80 % by mass from oxygenated monoterpenes. Of the single-component experiments, VOC mixing ratios were Gas-phase VOC profiles observed during the SOA experi- estimated to be 115 ppb for eucalyptol via its injection rate ments using real plants were characterised at the inlet of the through the syringe pump, whereas camphor and camphene PAM flow reactor. Samples were collected by trapping VOCs could not be estimated using this approach due to their intro- onto multi-bed adsorbent cartridges containing Carbograph duction via sublimation. Thus, VOC mixing ratios for cam- 5TD and Tenax TA adsorbents (Markes International, part phor were estimated to be 61 ppb on the basis of the SOA

Atmos. Chem. Phys., 20, 10953–10965, 2020 https://doi.org/10.5194/acp-20-10953-2020 A. Mehra et al.: Oligomer and HOM formation from oxidation of oxygenated monoterpenes 10957 mass yield from the plants, which under low-NO, no-seed Sage and Artemisia plant emissions under low- and medium- conditions was approximately 8 % for mass loadings rang- NOx conditions. ing from 4 to 19 µg m−3, similar to that for other monoterpenes such as α-pinene (Donahue et al., 2012; Shilling et 3.2 Overview of SOA composition al., 2008). An 8 % yield from eucalyptol would correspond to an estimated 130 ppb at the inlet, which is similar to the Here, we utilise the ions identified in each experiment to 115 ppb calculated based on the syringe pump injection rate carry out a qualitative comparison of the SOA composition and dilution. For camphene, the VOC mixing ratios are esti- between the different VOC precursors and plants. Figure 2a mated to be 30 ppb, based on a reported yield from β-pinene shows a Venn diagram of the number of distinct molecular from PAM-OFR experiments (Friedman and Farmer, 2018). formulas used in the high-resolution ion peak lists for cam- Calculations of remaining VOC for the single-component ex- phene, camphor and eucalyptol spectra. A majority of the as- periments show that all VOCs are reacted under the OH ex- signed ions are unique to each of the precursors, and a small posures employed in this study, thereby validating the use of number of ions are non-unique (i.e. are present in the mass the aerosol yield itself to estimate VOC concentrations. spectra of all three of the precursors). The relatively small A summary of the measured and estimated VOC con- number of non-unique ions (39) formed from all of the pre- centrations are included in Table 2 as well as aerosol mass cursors contributes to > 70 % of the product signal observed (Fig. 2b). The unique ion signal is minor and is distributed concentrations, OH exposures, modelled NOx conditions, across many more ions (80–437; Fig. 2a). Due to the rela- VOC/OH and VOC/NOx ratios. The “OH exposure with VOCs” accounts for reductions in OH exposure following tively low signal intensity of these individual unique ions, it additions of VOCs (Li et al., 2015). The intervals presented is not deemed suitable to use them as markers, particularly as in Table 2 represents aerosol that was collected over a period there is ambiguity in their assignment under the limited res- of 20–30 min after aerosol mass concentrations stabilised; olution of the mass spectrometer and potential artefacts due thus, each setting represents an integrated average that was to thermal decomposition caused by the FIGAERO. The per- analysed as a single mass spectrum. One averaging interval centage of signal from the 20 highest intensity ions (Fig. 3) was used to characterise the aerosol composition for each shows that the complexity of SOA from plants is greater than that of single components, as up to 40 %–60 % of the prod- VOC system under low- and medium-NOx conditions. uct signal can be attributed to the top 20 ions. The top 20 ions observed under low- and medium-NOx conditions are listed in Tables S1 and S2 in the Supplement respectively. 3 Results and discussion 3.3 HOM and oligomer formation 3.1 VOC emissions from plants Figure 4 plots the ions observed during all experiments ac- Figure 1 shows a single snapshot of the VOC composi- cording to their carbon and oxygen numbers. This figure tion from these plants, measured by TD-GC-FID–ToF-MS, highlights some of the differences in the SOA spectra be- to note the main features relevant for the SOA composi- tween the single precursors and the plant emissions. Oxida- tion measured with I-CIMS. Both Sage and Artemisia plant tion of camphene yields mainly small, low mass (Fig. S1), emission profiles are dominated by oxygenated monoter- molecular fragmentation products (< C10) as compared with penes (72 % and 79 % respectively), which is the least stud- camphor and eucalyptol which have many more products at ied BVOC type (Goldstein and Galbally, 2007), while other higher carbon numbers. The bulk of the signal for camphene monoterpenes have a small contribution (20 % and 13 % re- SOA is spread amongst fragmentation products, whereas for spectively). For Artemisia, eucalyptol contributes a larger camphor it is a mixture between fragmentation and those re- proportion of the signal than camphor (25 % and 5 % re- taining the carbon backbone of the precursor (Fig. 2, vertical spectively), whereas camphor alone dominates the emission black line). The presence of oxidised fragmentation products profile of Sage (57 %). Artemisia has a large contribution in the case of camphene potentially shows that there is an (49 %) from other oxygenated monoterpene species. The spe- increased prevalence of fragmentation pathways during the ciation of VOC emissions varies between the two plants, and oxidation of camphene, whereas the oxidation of camphor the detailed VOC profiles and SOA yields will be presented and eucalyptol proceed via pathways that retain their carbon in a separate paper. Of the monoterpenes, the composition backbone more readily. In eucalyptol SOA, for example, a of SOA from camphene is least well characterised due to large proportion of the signal can be attributed to oxidised its low reactivity with ozone; however, it is highly reactive C10 products which form with no fragmentation of the carbon with hydroxyl radical (Gaona-Colmán et al., 2017) and is, backbone, and there is a larger contribution from oligomers therefore, studied in detail in this paper. The following sec- (≥ C11). tion focuses on the characterisation and comparison of SOA from the photooxidation of camphor, camphene and eucalyptol alongside SOA produced from the photooxidation of the https://doi.org/10.5194/acp-20-10953-2020 Atmos. Chem. Phys., 20, 10953–10965, 2020 10958 A. Mehra et al.: Oligomer and HOM formation from oxidation of oxygenated monoterpenes

Table 2. Summary of experimental conditions, where the VOC mixing ratios denoted by a are measured by TD-GC-FID–ToF-MS, those denoted by b are estimated from syringe pump injection, those denoted by c are estimated from SOA yields of β-pinene and those denoted by d are estimated from SOA yields of plant experiments.

Precursor NOx VOC mixing AMS aerosol mass OH exposure NO NO2 VOC/OH VOC/NOx condition ratios (ppb) concentrations with VOCs without VOCs (ppb) (ppb) (µg m−3)(×1011 molec. cm−3) Artemisia Low 27a 9.35 10.02 – 0 0 48.7 Med 28a – 5.29 – 2.1 51.8 97.7 0.52 Sage Low 28a 18 7.32 – 0 0 70.6 Med 34a – 4.09 – 1.7 48.5 154 0.68 Camphene Low 30c 20 10.14 10.1 0 0 48.7 Med – 4.57 4.16 2.2 58.4 121 0.49 Camphor Low 61d 30 9.33 8.58 0 0 121 Med – 4.67 3.77 2.2 57.0 241 1.03 Eucalyptol Low 115b 66 7.16 5.51 0 0 296 Med – 3.54 2.11 1.9 57.9 600 1.93

Figure 1. Volatile organic compound emission proﬁles of (a) Sage and (b) Artemisia where OxMTs are oxygenated monoterpenes, MTs are monoterpenes and SQT are sesquiterpenes.

Despite different species contributing to the emissions pro- determined from AMS for the low-NOx conditions. The av- ﬁles for the two plants, the bulk composition and average erage molecular formulas for each condition, obtained by molecular formulas are similar (Table 3). A potential expla- averaging over the distributions for each element, are also nation for this is the similar contributions from oxygenated shown. Table 3 indicates that increasing NOx results in a monoterpenes (Fig. 1), which may have similar SOA charac- slight increase in O/C across most of the systems. The aver- teristics despite different speciation. The monomer region of age molecular formulas indicate that this increase is caused plant SOA (≤ C10) can be attributed to fragmentation prod- by both a slight decrease in the average C number and an in- ucts from all VOCs. However, the presence of oligomers crease in the average O number. Fewer high-carbon-number (≥ C11) in the plant SOA is likely to be from products associ- products are observed under medium-NOx conditions for all ated with the oxygenated monoterpenes, as camphene shows precursors; however, this effect is more notable in the single- few oligomer products (Fig. 4). component experiments than in the plant SOA, where low- Table 3 shows the average O/C of I-CIMS calculated by and medium-NOx conditions look largely similar (Fig. 4). averaging across molecular formulas as well as the bulk O/C Under medium-NOx conditions, nitrogen-containing prod-

Atmos. Chem. Phys., 20, 10953–10965, 2020 https://doi.org/10.5194/acp-20-10953-2020 A. Mehra et al.: Oligomer and HOM formation from oxidation of oxygenated monoterpenes 10959

Figure 2. (a) Comparison of ions from peak lists of individual volatile organic compound precursors (number of ions shown in Venn diagram). (b) The contribution of unique and non-unique products to the total signal derived from the Venn diagram under low-NOx conditions.

Figure 3. Contribution of the top 20 ions to observed product signal. ucts are observed, with the largest contributions to the sig- study aims to compare the relative contributions of different nal in camphor (35 %), followed by Sage (30 %), camphene SOA components across the different single-precursor and (28 %), Artemisia (19 %) and eucalyptol (7 %). plant experiments rather than quantifying the absolute con- Two key pathways of SOA formation from BVOCs have tributions of any of the components. Owing to the similarity been identified: the formation of highly oxygenated organic in composition across these systems, we expect that the ratios molecules (HOM) (Bianchi et al., 2019; Ehn et al., 2014; described here are not significantly affected by uncertainties Jokinen et al., 2014; Tu et al., 2016) and oligomerisation in quantification. (Hall and Johnston, 2011; Kourtchev et al., 2016; Kundu et Our results show the large contributions of HOMs to the al., 2012; Putman et al., 2011; Tolocka et al., 2004). HOMs total product signal from the oxygenated monoterpenes of are defined here as ions that contain six or more oxygen up to 40 %, whereas the contributions of HOMs to cam- atoms (Bianchi et al., 2019). Figure 5 shows the relative con- phene SOA are as low as 12 %–14 % (Fig. 5). HOMs show tributions of HOM and oligomer products to the observed minimal differences in their contribution to the signal be- signal for the different precursors and plants, aiding in the tween low- and medium-NOx conditions, whereas oligomers evaluation of the relative importance of different SOA for- show a decrease in all cases with NOx addition. This sug- mation pathways under low- and medium-NOx conditions. gests that HOM formation itself, a rapid intramolecular pro- The products detected by I-CIMS are typically multifunc- cess, is not hindered by NOx under these conditions, whereas tional oxidised species, which do not fully represent the SOA NO hinders oligomerisation. Figure 5 also indicates that the formed from a given system. Thus, the I-CIMS signal repre- oligomer content in SOA is highest for oxygenated monoter- sents only a portion of the SOA, and the reported contribu- penes. Previous studies of mixtures have shown the oligomer tions of this portion are likely to be an upper bound of the content to be similar to that of α-pinene alone (Kourtchev et contribution of oligomers and HOM to the total SOA. This al., 2016). However, our results suggest that in plant species https://doi.org/10.5194/acp-20-10953-2020 Atmos. Chem. Phys., 20, 10953–10965, 2020 10960 A. Mehra et al.: Oligomer and HOM formation from oxidation of oxygenated monoterpenes

Figure 4. Carbon vs. oxygen plot for aerosol-phase composition under low- and medium-NOx conditions for volatile organic compound precursors and plants. (The vertical black line separates monomers and oligomers in carbon-number space, and the symbols are proportional to the ion intensity.)

Table 3. Bulk composition of secondary organic aerosol from single-component standards and plants.

Precursor Condition O/C I-CIMS O/C AMS CXHY OZ

Camphene Low NOx 0.69 0.70 C7.26H9.85O4.03 Medium NOx 0.74 – C6.63H9.7N0.12O4.21

Camphor Low NOx 0.66 0.64 C8.97H12.34O4.8 Medium NOx 0.66 – C8.34H11.98N0.07O4.71

Eucalyptol Low NOx 0.58 0.52 C9.45H13.09O4.85 Medium NOx 0.65 – C8.47H12.37N0.01O5.06

Sage Low NOx 0.74 0.78 C9.54H13.30O4.52 Medium NOx 0.66 – C8.42H12.34N0.09O4.66

Artemisia Low NOx 0.67 0.74 C8.51H11.79O4.58 Medium NOx 0.71 – C7.62H11.07 N0.06O4.65 which emit low amounts of α-pinene, such as Sage and ies, and this could inﬂuence the extent to which oligomers Artemisia, other VOCs such as camphor and eucalyptol may contribute to SOA (Kourtchev et al., 2016). However, the es- become important for oligomer formation. It should be noted timated VOC mixing ratios for the other single-component that VOC concentrations were higher in the case of eucalyp- and plant experiments were more similar to one another. Fur- tol compared with the other single-component and plant stud- thermore, the oligomer content observed in the plant exper-

Atmos. Chem. Phys., 20, 10953–10965, 2020 https://doi.org/10.5194/acp-20-10953-2020 A. Mehra et al.: Oligomer and HOM formation from oxidation of oxygenated monoterpenes 10961

Figure 5. Comparison of the proportion of the signal attributable to oligomeric species (a) and highly oxygenated organic molecules (b). iments, which had lower VOC mixing ratios than that of tory studies should encompass a broader range of VOC/OH the single-component experiments, are comparable to that of and VOC/NOx ratios, due to the potential influence this has camphor. on the proportion of oligomers formed (Kourtchev et al., 2016), alongside seed acidity and humidity dependence. In addition, there are uncertainties pertaining to the absolute 4 Conclusions and implications contributions of HOM and oligomer products to the SOA from these plant and precursor systems owing to challenges Emissions of VOCs from Sage and Artemisia plants, which calibrating for these oxidised products for which no stan- are widespread in California and much of the western United dards exist. These uncertainties may influence the absolute States, are different from those of other commonly stud- magnitude of the contributions of these compound classes ied plants such as conifers and broad-leaved trees, as emis- to SOA. This study provides insights into the SOA forma- sions of oxygenated monoterpenes are the largest fraction. tion from VOC systems not previously studied with respect Here, we have presented a detailed chemical characterisa- to their SOA formation potential, and these results should be tion of SOA from Sage and Artemisia plants, from two oxy- taken as a basis upon which to study their potential impor- genated monoterpene precursors emitted by these species tance for ambient SOA formation in more detail. (camphor and eucalyptol) and from a monoterpene (cam- Sage plants emit a mixture of BVOCs, and SOA formed phene). Results show that up to 40 % of the product signal from their emissions shows greater complexity than sin- was from HOMs for the oxygenated monoterpene precur- gle components, although the majority of ions observed are sors and that clear oligomerisation was observed. Under el- generic monoterpene oxidation products emitted from all of evated NO conditions, HOM formation did not change sig- x the investigated VOCs. Thus, constraining VOC contribu- nificantly. However, oligomerisation was reduced for all pre- tions to SOA in complex mixtures remains a challenge. Our cursors and plants. results clearly show that HOMs can contribute up to 33 % This study shows that HOM and oligomer formation is of the signal in the plant emission mixtures and oligomerisa- potentially important for SOA formed from the oxidation of tion continues to be a significant fraction of the SOA. This oxygenated monoterpenes. These compounds are commonly indicates that oxygenated monoterpenes may be key to un- emitted by woody shrubs, but they have not been the sub- derstanding SOA in regions with many Sage plants or other ject of previous SOA studies. Owing to the potential of these high oxygenated monoterpene-emitting plant species. VOCs to form HOM and oligomer products, future labora- https://doi.org/10.5194/acp-20-10953-2020 Atmos. Chem. Phys., 20, 10953–10965, 2020 10962 A. Mehra et al.: Oligomer and HOM formation from oxidation of oxygenated monoterpenes

This is the first detailed study of oxygenated monoterpene References SOA chemistry using both single-component standards and real plant emissions. Eucalypts, which are dominant emit- ters of eucalyptol, are present globally, comprise many dif- Bannan, T. J., Le Breton, M., Priestley, M., Worrall, S. D., Bacak, ferent species and are likely globally important for SOA for- A., Marsden, N. A., Mehra, A., Hammes, J., Hallquist, M., Al- farra, M. R., Krieger, U. K., Reid, J. P., Jayne, J., Robinson, mation. Previously reported low thresholds of new particle W., McFiggans, G., Coe, H., Percival, C. J., and Topping, D.: A formation from species containing high proportions of oxy- method for extracting calibrated volatility information from the genated monoterpenes (Mentel et al., 2009) could be ex- FIGAERO-HR-ToF-CIMS and its experimental application, At- plained by the high oligomer content of the SOA we observed mos. Meas. Tech., 12, 1429–1439, https://doi.org/10.5194/amt- for these VOCs and in the mixtures. High oligomer con- 12-1429-2019, 2019. tent has been shown to influence particle viscosity by intra- Berndt, T., Richters, S., Jokinen, T., Hyttinen, N., Kurtén, T., and inter-molecular hydrogen bonding between oligomers Otkjaer, R. V, Kjaergaard, H. G., Stratmann, F., Herrmann, (Huang et al., 2018); thus, our results could indicate very dif- H., Sipilä, M., Kulmala, M., Ehn, M., Otkjær, R. V., Kjaer- ferent physicochemical properties for SOA generated from gaard, H. G., Stratmann, F., Herrmann, H., Sipilä, M., Kul- plants that contain high proportions of oxygenated monoter- mala, M., and Ehn, M.: Hydroxyl radical-induced formation of penes. highly oxidized organic compounds, Nat. Commun., 7, 13677, https://doi.org/10.1038/ncomms13677, 2016. Bianchi, F., Kurtén, T., Riva, M., Mohr, C., Rissanen, M. P., Roldin, P., Berndt, T., Crounse, J. D., Wennberg, P. O., Mentel, T. F., Data availability. Data are available upon request from the corre- Wildt, J., Junninen, H., Jokinen, T., Kulmala, M., Worsnop, D. sponding authors. R., Thornton, J. A., Donahue, N., Kjaergaard, H. G., and Ehn, M.: Highly Oxygenated Organic Molecules (HOM) from Gas- Phase Autoxidation Involving Peroxy Radicals: A Key Con- Supplement. The supplement related to this article is available on- tributor to Atmospheric Aerosol, Chem. Rev., 119, 3472–3509, line at: https://doi.org/10.5194/acp-20-10953-2020-supplement. https://doi.org/10.1021/acs.chemrev.8b00395, 2019. Carlton, A. G., Wiedinmyer, C., and Kroll, J. H.: A review of Sec- ondary Organic Aerosol (SOA) formation from isoprene, Atmos. Author contributions. CF designed the experiments. Instrument de- Chem. Phys., 9, 4987–5005, https://doi.org/10.5194/acp-9-4987- ployment and operation were carried out by CF, AM, JEK, CS, LW 2009, 2009. and FK. Aerosol mass spectrometer analysis was carried out by CF. Carlton, A. G., Pye, H. O. T., Baker, K. R., and Hen- AM carried out the analysis using the time-of-flight chemical ioni- nigan, C. J.: Additional Benefits of Federal Air-Quality sation mass spectrometer and wrote the paper. AG and CS ran the Rules: Model Estimates of Controllable Biogenic Secondary volatile sample analysis. All co-authors discussed the results and Organic Aerosol, Environ. Sci. Technol., 52, 9254–9265, commented on the paper. https://doi.org/10.1021/acs.est.8b01869, 2018. Ceacero-Vega, A. A., Ballesteros, B., Bejan, I., Barnes, I., Jimeìnez, E., and Albaladejo, J.: Kinetics and Mechanisms Competing interests. The authors declare that they have no conflict of the Tropospheric Reactions of Menthol, Borneol, Fenchol, of interest. Camphor, and Fenchone with Hydroxyl Radicals (OH) and Chlorine Atoms (Cl), J. Phys. Chem. A, 116, 4097–4107, https://doi.org/10.1021/jp212076g, 2012. Acknowledgements. Archit Mehra is fully funded by the Natural Chung, S. H. and Seinfeld, J. H.: Global distribution and climate Environment Research Council (NERC) and acknowledges funding forcing of carbonaceous aerosols, J. Geophys. Res, 107, 4407, from a NERC EAO doctoral training partnership and an Aerodyne https://doi.org/10.1029/2001JD001397, 2002. Research Inc. CASE partnership. Claeys, M., Wang, W., Ion, A. C., Kourtchev, I., Gelencse, A., and Maenhaut, W.: Formation of secondary organic aerosols from isoprene and its gas-phase oxidation products through reaction with hydrogen peroxide, Atmos. Environ., 38, 4093–4098, Financial support. This research has been supported by the Natural https://doi.org/10.1016/j.atmosenv.2004.06.001, 2004. Environment Research Council (grant no. NE/L002469/1). Corchnoy, S. B. and Atkinson, R.: Kinetics of the gas-phase reactions of hydroxyl and nitrogen oxide (NO3) radicals with 2- carene, 1,8-cineole, p-cymene, and terpinolene, Environ. Sci. Review statement. This paper was edited by Alex Lee and reviewed Technol., 24, 1497–1502, https://doi.org/10.1021/es00080a007, by two anonymous referees. 1990. DeCarlo, P. F., Kimmel, J. R., Trimborn, A., Northway, M. J., Jayne, J. T., Aiken, A. C., Gonin, M., Fuhrer, K., Horvath, T., Docherty, K. S., Worsnop, D. R., and Jimenez, J. L.: Field-deployable, high-resolution, time-of-flight aerosol mass spectrometer, Anal. Chem., 78, 8281–8289, https://doi.org/10.1021/ac061249n, 2006.

Atmos. Chem. Phys., 20, 10953–10965, 2020 https://doi.org/10.5194/acp-20-10953-2020 A. Mehra et al.: Oligomer and HOM formation from oxidation of oxygenated monoterpenes 10963

Després, V. R., Huffman, A. J., Burrows, S. M., Hoose, C., Safa- Friedman, B. and Farmer, D. K.: SOA and gas phase or- tov, A. S., Buryak, G., Fröhlich-Nowoisky, J., Elbert, W., An- ganic acid yields from the sequential photooxidation dreae, M. O., Pöschl, U., and Jaenicke, R.: Primary biologi- of seven monoterpenes, Atmos. Environ., 187, 335–345, cal aerosol particles in the atmosphere: A review, Tellus B, 64, https://doi.org/10.1016/j.atmosenv.2018.06.003, 2018. 15598, https://doi.org/10.3402/tellusb.v64i0.15598, 2012. Gaona-Colmán, E., Blanco, M. B., Barnes, I., Weisen, P., and Donahue, N. M., Kroll, J. H., Pandis, S. N., and Robinson, A. L.: Teruel, M. A.: OH- and O3-initiated atmospheric degrada- A two-dimensional volatility basis set – Part 2: Diagnostics of tion of camphene: temperature dependent rate coefficients, organic-aerosol evolution, Atmos. Chem. Phys., 12, 615–634, product yields and mechanisms, RSC Adv., 7, 2733–2744, https://doi.org/10.5194/acp-12-615-2012, 2012. https://doi.org/10.1039/c6ra26656h, 2017. Dudareva, N., Negre, F., Nagegowda, D. A., and Orlova, Gentner, D. R., Ormeño, E., Fares, S., Ford, T. B., Weber, R., Park, I.: Plant volatiles: Recent advances and future per- J.-H., Brioude, J., Angevine, W. M., Karlik, J. F., and Goldstein, spectives, CRC. Crit. Rev. Plant Sci., 25, 417–440, A. H.: Emissions of terpenoids, benzenoids, and other biogenic https://doi.org/10.1080/07352680600899973, 2006. gas-phase organic compounds from agricultural crops and their Ehn, M., Thornton, J. A., Kleist, E., Sipilä, M., Junninen, H., potential implications for air quality, Atmos. Chem. Phys., 14, Pullinen, I., Springer, M., Rubach, F., Tillmann, R., Lee, B., 5393–5413, https://doi.org/10.5194/acp-14-5393-2014, 2014. Lopez-Hilfiker, F., Andres, S., Acir, I. H., Rissanen, M., Joki- Goldstein, A. H. and Galbally, I. E.: Known and unexplored organic nen, T., Schobesberger, S., Kangasluoma, J., Kontkanen, J., constituents in the earth’s atmosphere, Environ. Sci. Technol., 41, Nieminen, T., Kurtén, T., Nielsen, L. B., Jørgensen, S., Kjaer- 1514–1521, https://doi.org/10.1021/es072476p, 2007. gaard, H. G., Canagaratna, M., Dal Maso, M., Berndt, T., Guenther, A.: Biological and Chemical Diversity of Biogenic Petäjä, T., Wahner, A., Kerminen, V. M., Kulmala, M., Worsnop, Volatile Organic Emissions into the Atmosphere, ISRN Atmos. D. R., Wildt, J., and Mentel, T. F.: A large source of low- Sci., 2013, 786290, https://doi.org/10.1155/2013/786290, 2013. volatility secondary organic aerosol, Nature, 506, 476–479, Guenther, A., Hewitt, C. N., Erickson, D., Guenther, A., He- https://doi.org/10.1038/Nature13032, 2014. witt, N. C., Erickson, D., Fall, R., Geron, C., Graedel, T., Faiola, C. L., Erickson, M. H., Fricaud, V. L., Jobson, B. T., and Harley, P., Klinger, L., Lerdau, M., Mckay, W. A., Pierce, VanReken, T. M.: Quantification of biogenic volatile organic T., Scholes, B., Steinbrecher, R., Tallamraju, R., Taylor, J., compounds with a flame ionization detector using the effec- and Zimmerman, P.: A global model of natural volatile or- tive carbon number concept, Atmos. Meas. Tech., 5, 1911–1923, ganic compound emissions, J. Geophys. Res., 100, 8873–8892, https://doi.org/10.5194/amt-5-1911-2012, 2012. https://doi.org/10.1029/94JD02950, 1995. Faiola, C. L., Wen, M., and VanReken, T. M.: Chemical char- Guenther, A. B., Jiang, X., Heald, C. L., Sakulyanontvittaya, acterization of biogenic secondary organic aerosol generated T., Duhl, T., Emmons, L. K., and Wang, X.: The Model of from plant emissions under baseline and stressed conditions: Emissions of Gases and Aerosols from Nature version 2.1 inter- and intra-species variability for six coniferous species, At- (MEGAN2.1): an extended and updated framework for mod- mos. Chem. Phys., 15, 3629–3646, https://doi.org/10.5194/acp- eling biogenic emissions, Geosci. Model Dev., 5, 1471–1492, 15-3629-2015, 2015. https://doi.org/10.5194/gmd-5-1471-2012, 2012. Faiola, C. L., Buchholz, A., Kari, E., Yli-Pirilä, P., Holopainen, J. Hall, W. A. and Johnston, M. V.: Oligomer Content of α-Pinene K., Kivimäenpää, M., Miettinen, P., Worsnop, D. R., Lehtinen, Secondary Organic Aerosol, Aerosol Sci. Technol., 45, 37–45, K. E. J., Guenther, A. B., and Virtanen, A.: Terpene Compo- https://doi.org/10.1080/02786826.2010.517580, 2011. sition Complexity Controls Secondary Organic Aerosol Yields Hao, L. Q., Yli-Pirilä, P., Tiitta, P., Romakkaniemi, S., Vaatto- from Scots Pine Volatile Emissions, Nat. Sci. Rep., 8, 3053, vaara, P., Kajos, M. K., Rinne, J., Heijari, J., Kortelainen, A., https://doi.org/10.1038/s41598-018-21045-1, 2018. Miettinen, P., Kroll, J. H., Holopainen, J. K., Smith, J. N., Faiola, C. L., Pullinen, I., Buchholz, A., Khalaj, F., Ylisirniö, A., Joutsensaari, J., Kulmala, M., Worsnop, D. R., and Laaksonen, Kari, E., Miettinen, P., Holopainen, J. K., Kivimäenpää, M., A.: New particle formation from the oxidation of direct emis- Schobesberger, S., Yli-Juuti, T., and Virtanen, A.: Secondary sions of pine seedlings, Atmos. Chem. Phys., 9, 8121–8137, Organic Aerosol Formation from Healthy and Aphid-Stressed https://doi.org/10.5194/acp-9-8121-2009, 2009. Scots Pine Emissions, ACS Earth Space Chem., 3, 1756–1772, Hao, L. Q., Romakkaniemi, S., Yli-Pirilä, P., Joutsensaari, J., Ko- https://doi.org/10.1021/acsearthspacechem.9b00118, 2019. rtelainen, A., Kroll, J. H., Miettinen, P., Vaattovaara, P., Tiitta, P., Fiore, A. M., Naik, V., Spracklen, D. V, Steiner, A., Unger, N., Jaatinen, A., Kajos, M. K., Holopainen, J. K., Heijari, J., Rinne, Prather, M., Bergmann, D., Cameron-Smith, P. J., Cionni, I., J., Kulmala, M., Worsnop, D. R., Smith, J. N., and Laaksonen, Collins, W. J., Dalsøren, S., Eyring, V., Folberth, G. A., Ginoux, A.: Mass yields of secondary organic aerosols from the oxidation P., Horowitz, L. W., Josse, B., Lamarque, J.-F., Mackenzie, I. of α-pinene and real plant emissions, Atmos. Chem. Phys., 11, A., Nagashima, T., O ’connor, F. M., Righi, M., Rumbold, S. T., 1367–1378, https://doi.org/10.5194/acp-11-1367-2011, 2011. Shindell, D. T., Skeie, R. B., Sudo, K., Szopa, S., Takemura, T., Hoffmann, T., Odum, J. R., Bowman, F., Collins, D., Klockow, D., and Zeng, G.: Global air quality and climate, Chem. Soc. Rev., Flagan, R. C., and Seinfeld, J. H.: Formation of Organic Aerosols 41, 6663–6683, https://doi.org/10.1039/c2cs35095e, 2012. from the Oxidation of Biogenic Hydrocarbons, J. Atmos. Chem., Forster, P., Ramaswamy, V., Artaxo, P., Berntsen, T., Betts, R., Fa- 26, 189–222, 1997. hey, D. W., Haywood, J., Lean, J., Lowe, D. C., Myhre, G., Huang, W., Saathoff, H., Pajunoja, A., Shen, X., Naumann, K.- Nganga, J., Prinn, R., Raga, G., Schulz, M., and Van, R.: Changes H., Wagner, R., Virtanen, A., Leisner, T., and Mohr, C.: α- in Atmospheric Constituents and in Radiative Forcing, in: Cli- Pinene secondary organic aerosol at low temperature: chem- mate Change, IPCC, Geneva, Switzerland, 2007. ical composition and implications for particle viscosity, At-

https://doi.org/10.5194/acp-20-10953-2020 Atmos. Chem. Phys., 20, 10953–10965, 2020 10964 A. Mehra et al.: Oligomer and HOM formation from oxidation of oxygenated monoterpenes

mos. Chem. Phys., 18, 2883–2898, https://doi.org/10.5194/acp- Lamarque, J.-F., Bond, T. C., Eyring, V., Granier, C., Heil, A., 18-2883-2018, 2018. Klimont, Z., Lee, D., Liousse, C., Mieville, A., Owen, B., Jimenez, J. L., Canagaratna, M. R., Donahue, N. M., Prevot, A. S. Schultz, M. G., Shindell, D., Smith, S. J., Stehfest, E., Van H., Zhang, Q., Kroll, J. H., DeCarlo, P. F., Allan, J. D., Coe, Aardenne, J., Cooper, O. R., Kainuma, M., Mahowald, N., H., Ng, N. L., Aiken, A. C., Docherty, K. S., Ulbrich, I. M., McConnell, J. R., Naik, V., Riahi, K., and van Vuuren, D. Grieshop, A. P., Robinson, A. L., Duplissy, J., Smith, J. D., Wil- P.: Historical (1850–2000) gridded anthropogenic and biomass son, K. R., Lanz, V. A., Hueglin, C., Sun, Y. L., Tian, J., Laak- burning emissions of reactive gases and aerosols: methodol- sonen, A., Raatikainen, T., Rautiainen, J., Vaattovaara, P., Ehn, ogy and application, Atmos. Chem. Phys., 10, 7017–7039, M., Kulmala, M., Tomlinson, J. M., Collins, D. R., Cubison, M. https://doi.org/10.5194/acp-10-7017-2010, 2010. J., Dunlea, J., Huffman, J. A., Onasch, T. B., Alfarra, M. R., Lambe, A. T., Ahern, A. T., Williams, L. R., Slowik, J. G., Wong, Williams, P. I., Bower, K., Kondo, Y., Schneider, J., Drewnick, J. P. S., Abbatt, J. P. D., Brune, W. H., Ng, N. L., Wright, J. P., F., Borrmann, S., Weimer, S., Demerjian, K., Salcedo, D., Cot- Croasdale, D. R., Worsnop, D. R., Davidovits, P., and Onasch, trell, L., Griffin, R., Takami, A., Miyoshi, T., Hatakeyama, S., T. B.: Characterization of aerosol photooxidation flow reac- Shimono, A., Sun, J. Y., Zhang, Y. M., Dzepina, K., Kimmel, tors: heterogeneous oxidation, secondary organic aerosol for- J. R., Sueper, D., Jayne, J. T., Herndon, S. C., Trimborn, A. mation and cloud condensation nuclei activity measurements, M., Williams, L. R., Wood, E. C., Middlebrook, A. M., Kolb, Atmos. Meas. Tech., 4, 445–461, https://doi.org/10.5194/amt-4- C. E., Baltensperger, U., and Worsnop, D. R.: Evolution of Or- 445-2011, 2011. ganic Aerosols in the Atmosphere, Science, 326, 1525–1529, Lambe, A., Massoli, P., Zhang, X., Canagaratna, M., Nowak, J., https://doi.org/10.1126/science.1180353, 2009. Daube, C., Yan, C., Nie, W., Onasch, T., Jayne, J., Kolb, C., Jokinen, T., Sipilä, M., Richters, S., Kerminen, V. M., Paasonen, P., Davidovits, P., Worsnop, D., and Brune, W.: Controlled nitric 1 Stratmann, F., Worsnop, D., Kulmala, M., Ehn, M., Herrmann, oxide production via O( D) + N2O reactions for use in oxida- H., and Berndt, T.: Rapid autoxidation forms highly oxidized tion flow reactor studies, Atmos. Meas. Tech., 10, 2283–2298, RO2 radicals in the atmosphere, Angew. Chem. Int. Ed., 53, https://doi.org/10.5194/amt-10-2283-2017, 2017. 14596–14600, https://doi.org/10.1002/anie.201408566, 2014. Lee, B. H., Lopez-Hilfiker, F. D., Mohr, C., Kurtén, T., Worsnop, Joutsensaari, J., Loivamäki, M., Vuorinen, T., Miettinen, P., Nerg, D. R., Thornton, J. A., Kurte, T., Worsnop, D. R., Thornton, A.-M., Holopainen, J. K., and Laaksonen, A.: Nanoparticle for- J. A., Kurtén, T., Worsnop, D. R., and Thornton, J. A.: An mation by ozonolysis of inducible plant volatiles, Atmos. Chem. iodide-adduct high-resolution time-of-flight chemical-ionization Phys., 5, 1489–1495, https://doi.org/10.5194/acp-5-1489-2005, mass spectrometer: Application to atmospheric inorganic and 2005. organic compounds, Environ. Sci. Technol., 48, 6309–6317, Joutsensaari, J., Yli-Pirilä, P., Korhonen, H., Arola, A., Blande, J. https://doi.org/10.1021/es500362a, 2014. D., Heijari, J., Kivimäenpää, M., Mikkonen, S., Hao, L., Mi- Li, R., Palm, B. B., Ortega, A. M., Hlywiak, J., Hu, W., Peng, ettinen, P., Lyytikäinen-Saarenmaa, P., Faiola, C. L., Laakso- Z., Day, D. A., Knote, C., Brune, W. H., De Gouw, J. A., and nen, A., and Holopainen, J. K.: Biotic stress accelerates forma- Jimenez, J. L.: Modeling the Radical Chemistry in an Oxidation tion of climate-relevant aerosols in boreal forests, Atmos. Chem. Flow Reactor: Radical Formation and Recycling, Sensitivities, Phys., 15, 12139–12157, https://doi.org/10.5194/acp-15-12139- and the OH Exposure Estimation Equation, J. Phys. Chem. A, 2015, 2015. 119, 4418–4432, https://doi.org/10.1021/jp509534k, 2015. Karban, R., Wetzel, W. C., Shiojiri, K., Ishizaki, S., Ramirez, S. R., Lohmann, U. and Feichter, J.: Global indirect aerosol ef- and Blande, J. D.: Deciphering the language of plant commu- fects: a review, Atmos. Chem. Phys., 5, 715–737, nication: Volatile chemotypes of sagebrush, New Phytol., 204, https://doi.org/10.5194/acp-5-715-2005, 2005. 380–385, https://doi.org/10.1111/nph.12887, 2014. Lopez-Hilfiker, F. D., Mohr, C., Ehn, M., Rubach, F., Kleist, E., Kourtchev, I., Giorio, C., Manninen, A., Wilson, E., Mahon, B., Wildt, J., Mentel, Th. F., Lutz, A., Hallquist, M., Worsnop, D., Aalto, J., Kajos, M., Venables, D., Ruuskanen, T., Levula, J., and Thornton, J. A.: A novel method for online analysis of gas Loponen, M., Connors, S., Harris, N., Zhao, D., Kiendler- and particle composition: description and evaluation of a Filter Scharr, A., Mentel, T., Rudich, Y., Hallquist, M., Doussin, J.- Inlet for Gases and AEROsols (FIGAERO), Atmos. Meas. Tech., F., Maenhaut, W., Bäck, J., Petäjä, T., Wenger, J., Kulmala, 7, 983–1001, https://doi.org/10.5194/amt-7-983-2014, 2014. M., and Kalberer, M.: Enhanced Volatile Organic Compounds Lopez-Hilfiker, F. D., Iyer, S., Mohr, C., Lee, B. H., D’Ambro, E. emissions and organic aerosol mass increase the oligomer L., Kurtén, T., and Thornton, J. A.: Constraining the sensitivity content of atmospheric aerosols, Nat. Publ. Gr., 6, 35038, of iodide adduct chemical ionization mass spectrometry to mul- https://doi.org/10.1038/srep35038, 2016. tifunctional organic molecules using the collision limit and ther- Kroll, J. H., Ng, N. L., Murphy, S. M., Flagan, R. C., and Se- modynamic stability of iodide ion adducts, Atmos. Meas. Tech., infeld, J. H.: Secondary Organic Aerosol Formation from Iso- 9, 1505–1512, https://doi.org/10.5194/amt-9-1505-2016, 2016. prene Photooxidation, Environ. Sci. Technol., 40, 1869–1877, McFiggans, G., Mentel, T. F., Wildt, J., Pullinen, I., Kang, S., Kleist, https://doi.org/10.1021/es0524301, 2006. E., Schmitt, S., Springer, M., Tillmann, R., Wu, C., Zhao, D., Kundu, S., Fisseha, R., Putman, A. L., Rahn, T. A., and Maz- Hallquist, M., Faxon, C., Le Breton, M., Hallquist, Å. M., Simp- zoleni, L. R.: High molecular weight SOA formation during son, D., Bergström, R., Jenkin, M. E., Ehn, M., Thornton, J. A., limonene ozonolysis: insights from ultrahigh-resolution FT-ICR Alfarra, M. R., Bannan, T. J., Percival, C. J., Priestley, M., Top- mass spectrometry characterization, Atmos. Chem. Phys., 12, ping, D., and Kiendler-Scharr, A.: Secondary organic aerosol re- 5523–5536, https://doi.org/10.5194/acp-12-5523-2012, 2012. duced by mixture of atmospheric vapours, Nature, 565, 587–593, https://doi.org/10.1038/s41586-018-0871-y, 2019.

Atmos. Chem. Phys., 20, 10953–10965, 2020 https://doi.org/10.5194/acp-20-10953-2020 A. Mehra et al.: Oligomer and HOM formation from oxidation of oxygenated monoterpenes 10965

Mentel, Th. F., Wildt, J., Kiendler-Scharr, A., Kleist, E., Till- Tolocka, M. P., Jang, M., Ginter, J. M., Cox, F. J., Kamens, mann, R., Dal Maso, M., Fisseha, R., Hohaus, Th., Spahn, H., R. M., and Johnston, M. V.: Formation of Oligomers in Sec- Uerlings, R., Wegener, R., Griffiths, P. T., Dinar, E., Rudich, ondary Organic Aerosol, Environ. Sci. Technol., 38, 1428–1434, Y., and Wahner, A.: Photochemical production of aerosols https://doi.org/10.1021/es035030r, 2004. from real plant emissions, Atmos. Chem. Phys., 9, 4387–4406, Tu, P., Hall, W. A., and Johnston, M. V.: Characterization https://doi.org/10.5194/acp-9-4387-2009, 2009. of Highly Oxidized Molecules in Fresh and Aged Biogenic Peng, Z., Day, D. A., Stark, H., Li, R., Lee-Taylor, J., Palm, B. B., Secondary Organic Aerosol, Anal. Chem., 88, 4495–4501, Brune, W. H., and Jimenez, J. L.: HOx radical chemistry in oxi- https://doi.org/10.1021/acs.analchem.6b00378, 2016. dation flow reactors with low-pressure mercury lamps systemati- Tyson, B. J., Dement, W. A., and Mooney, H. A.: Volatilisa- cally examined by modeling, Atmos. Meas. Tech., 8, 4863–4890, tion of terpenes from Salvia mellifera, Nature, 252, 119–121, https://doi.org/10.5194/amt-8-4863-2015, 2015. https://doi.org/10.1038/252119a0, 1974. Peng, Z., Palm, B. B., Day, D. A., Talukdar, R. K., Hu, W., VanReken, T. M., Greenberg, J. P., Harley, P. C., Guenther, A. B., Lambe, A. T., Brune, W. H., and Jimenez, J. L.: Model Eval- and Smith, J. N.: Direct measurement of particle formation and uation of New Techniques for Maintaining High-NO Con- growth from the oxidation of biogenic emissions, Atmos. Chem. ditions in Oxidation Flow Reactors for the Study of OH- Phys., 6, 4403–4413, https://doi.org/10.5194/acp-6-4403-2006, Initiated Atmospheric Chemistry, ACS Earth Sp. Chem., 2, 72– 2006. 86, https://doi.org/10.1021/acsearthspacechem.7b00070, 2018. Wyche, K. P., Ryan, A. C., Hewitt, C. N., Alfarra, M. R., McFig- Putman, A. L., Offenberg, J. H., Kundu, S., Rahn, T., Fis- gans, G., Carr, T., Monks, P. S., Smallbone, K. L., Capes, G., seha, R., Rahn, T. A., and Mazzoleni, L. R.: Ultrahigh- Hamilton, J. F., Pugh, T. A. M., and MacKenzie, A. R.: Emissions resolution FT-ICR mass spectrometry characterization of of biogenic volatile organic compounds and subsequent photo- a-pinene ozonolysis SOA, Atmos. Enviro., 46, 164–172, chemical production of secondary organic aerosol in mesocosm https://doi.org/10.1016/j.atmosenv.2011.10.003, 2011. studies of temperate and tropical plant species, Atmos. Chem. Quéléver, L. L. J., Kristensen, K., Normann Jensen, L., Rosati, Phys., 14, 12781–12801, https://doi.org/10.5194/acp-14-12781- B., Teiwes, R., Daellenbach, K. R., Peräkylä, O., Roldin, P., 2014, 2014. Bossi, R., Pedersen, H. B., Glasius, M., Bilde, M., and Ehn, Yli-Pirilä, P., Copolovici, L., Kännaste, A., Noe, S., Blande, J. D., M.: Effect of temperature on the formation of highly oxygenated Mikkonen, S., Klemola, T., Pulkkinen, J., Virtanen, A., Laak- organic molecules (HOMs) from alpha-pinene ozonolysis, At- sonen, A., Joutsensaari, J., Niinemets, Ü., and Holopainen, J. mos. Chem. Phys., 19, 7609–7625, https://doi.org/10.5194/acp- K.: Herbivory by an Outbreaking Moth Increases Emissions of 19-7609-2019, 2019. Biogenic Volatiles and Leads to Enhanced Secondary Organic Riva, M., Rantala, P., Krechmer, J. E., Peräkylä, O., Zhang, Y., Aerosol Formation Capacity, Environ. Sci. Technol., 50, 11501– Heikkinen, L., Garmash, O., Yan, C., Kulmala, M., Worsnop, 11510, https://doi.org/10.1021/acs.est.6b02800, 2016. D., and Ehn, M.: Evaluating the performance of five differ- Ylisirniö, A., Buchholz, A., Mohr, C., Li, Z., Barreira, L., Lambe, ent chemical ionization techniques for detecting gaseous oxy- A., Faiola, C., Kari, E., Yli-Juuti, T., Nizkorodov, S. A., genated organic species, Atmos. Meas. Tech., 12, 2403–2421, Worsnop, D. R., Virtanen, A., and Schobesberger, S.: Com- https://doi.org/10.5194/amt-12-2403-2019, 2019. position and volatility of secondary organic aerosol (SOA) Schobesberger, S., D’Ambro, E. L., Lopez-Hilfiker, F. D., Mohr, formed from oxidation of real tree emissions compared to C., and Thornton, J. A.: A model framework to retrieve ther- simplified volatile organic compound (VOC) systems, Atmos. modynamic and kinetic properties of organic aerosol from Chem. Phys., 20, 5629–5644, https://doi.org/10.5194/acp-20- composition-resolved thermal desorption measurements, Atmos. 5629-2020, 2020. Chem. Phys., 18, 14757–14785, https://doi.org/10.5194/acp-18- Zhang, X., Mcvay, R. C., Huang, D. D., Dalleska, N. F., Au- 14757-2018, 2018. mont, B., Flagan, R. C., and Seinfeld, J. H.: Formation and Shilling, J. E., Chen, Q., King, S. M., Rosenoern, T., Kroll, J. H., evolution of molecular products in α-pinene secondary or- Worsnop, D. R., McKinney, K. A., and Martin, S. T.: Particle ganic aerosol, P. Natl. Acad. Sci. USA, 112, 14168–14173, mass yield in secondary organic aerosol formed by the dark https://doi.org/10.1073/pnas.1517742112, 2015. ozonolysis of α-pinene, Atmos. Chem. Phys., 8, 2073–2088, Zhao, D. F., Buchholz, A., Tillmann, R., Kleist, E., Wu, C., https://doi.org/10.5194/acp-8-2073-2008, 2008. Rubach, F., Kiendler-Scharr, A., Rudich, Y., Wildt, J., and Stark, H., Yatavelli, R. L. N., Thompson, S. L., Kang, H., Krech- Mentel, T. F.: Environmental conditions regulate the im- mer, J. E., Kimmel, J. R., Palm, B. B., Hu, W., Hayes, P. L., pact of plants on cloud formation, Nat. Commun., 8, 1–8, Day, D. A., Campuzano-Jost, P., Canagaratna, M. R., Jayne, https://doi.org/10.1038/ncomms14067, 2017. J. T., Worsnop, D. R., and Jimenez, J. L.: Impact of Thermal Decomposition on Thermal Desorption Instruments: Advantage of Thermogram Analysis for Quantifying Volatility Distribu- tions of Organic Species, Environ. Sci. Technol., 51, 8491–8500, https://doi.org/10.1021/acs.est.7b00160, 2017.

https://doi.org/10.5194/acp-20-10953-2020 Atmos. Chem. Phys., 20, 10953–10965, 2020