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Ozone-initiated Terpene Reaction Products in Five European Offices: 1 Replacement of a Floor Cleaning Agent 2

3 A.W. Nørgaard,§ V. Kofoed-Sørensen,§ C. Mandin,# G. Ventura,¤ R. Mabilia,¶ E. Perreca,¶ A. 4 Cattaneo,‖ A. Spinazzè, V.G. Mihucz,† T. Szigeti,† Y. de Kluizenaar,∋ H.J.M. Cornelissen,∋ M. 5 Trantallidi,ψ P. Carrer,ψ I. Sakellaris,φ J. Bartzis,φ and P. Wolkoff,§,* 6 7 §National Research Centre for the Working Environment, 2100 Copenhagen Ø, Denmark 8 #Université Paris-Est, Centre scientifique et technique du bâtiment, 77447 Marne La Vallee Cedex 9 2, France 10 ¤IDMEC, University of Porto, 4200-465 Porto, Portugal 11 ¶CNR Institute for Atmospheric Pollution Research, Roma 1, Montelibretti, Italy 12 ‖‖Dept of Science and High Technology, University of Insubria, 22100 Como, Italy 13 †Cooperative Research Centre for Environmental Sciences, Eötvös Loránd University, H-1117 14 Budapest, Hungary 15 ∋The Netherlands Organization for Applied Scientific Research (TNO), 2600 AA Delft, The 16 Netherlands 17 ψ Dept of Biomedical and Clinical Sciences - Hospital L. Sacco, University of Milan, 20157 Milan, 18 Italy 19 φDept of Mechanical Engineering, University of West Macedonia, Kozani, West Macedonia, T. K. 20 50100, Greece 21 22 23 24 Keywords: 25 Acute symptoms 26 Floor cleaning agents 27 Indoor air quality 28 Intervention 29 Offices 30 Ozone-initiated reactions 31 Terpenes 32 33 34 35

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ABSTRACT: Cleaning agents often emit terpenes that react rapidly with ozone. These ozone-36 initiated reactions, which occur in the gas-phase and on surfaces, produce a host of gaseous and 37 particulate oxygenated compounds with possible adverse health effects in the eyes and airways. 38 Within the European Union (EU) project OFFICAIR, common ozone-initiated reaction products 39 were measured before and after the replacement of the regular floor cleaning agent with a 40 preselected low emitting floor cleaning agent in four offices located in four EU countries. One 41 reference office in a fifth country did not use any floor cleaning agent. Limonene, α-pinene, 3-42 carene, dihydromyrcenol, geraniol, linalool, and α-terpineol were targeted for measurement 43 together with the common terpene oxidation products formaldehyde, 4-acetyl-1-44 methylcyclohexene (4-AMCH), 3-isopropenyl-6-oxo-heptanal (IPOH), 6-methyl-5-heptene-2-one, 45 (6-MHO), 4-oxopentanal (4-OPA), and dihydrocarvone (DHC). Two-hour air samples on Tenax TA 46 and DNPH cartridges were taken in the morning, noon, and in the afternoon and analyzed by 47 thermal desorption combined with gas chromatography/mass spectrometry and HPLC/UV 48 analysis, respectively. Ozone was measured in all sites. All the regular cleaning agents emitted 49 terpenes, mainly limonene and linalool. After the replacement of the cleaning agent, substantially 50 lower concentrations of limonene and formaldehyde were observed. Some of the oxidation 51 product concentrations, in particular that of 4-OPA, were also reduced in line with limonene. 52 Maximum two-hour averaged concentrations of formaldehyde, 4-AMCH, 6-MHO, and IPOH would 53 not give rise to acute eye irritation-related symptoms in office workers; similarly, 6-AMCH, DHC 54 and 4-OPA would not result in airflow limitation to the airways. 55 56 57 58 59 60 FEATURES 61

• Ozone-initiated terpene oxidation products have been measured in offices. 62 • Change of regular to low terpene emitting floor cleaning agent showed lower limonene 63

and formaldehyde concentrations. 64 • Change of regular to low terpene emitting floor cleaning agent showed lower 4-65

oxopentanal concentration. 66 • Results indicated other sources of limonene and 4-oxopentanal. 67 • Measured oxidation products could not explain reported eye symptoms. 68

69 70 71 72

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INTRODUCTION 74 75 Cleaning agents may emit reactive compounds that affect the respiratory health among cleaning 76 personnel.1 Indoor exposure is also of health concern, due to in-situ ozone-initiated chemistry with 77 reactive volatile organic compounds (RVOCs).2 This is further exacerbated by the advent of stricter 78 energy efficiency measures, e.g., tighter building envelope and consequently possible lower air 79 exchange rate (AER) that may increase the concentration of RVOCs and time available for the 80 ozone-initiated reactions with terpenes (comprising terpenes and terpenoids). For instance, 81 limonene, an abundant and ubiquitous RVOC and a common fragrance component in numerous 82 products, such as air fresheners,3 readily undergoes ozonolysis to produce a complex mixture of 83 reaction products.4 Some reaction products are gaseous, e.g., formaldehyde5,6 and some have low 84 vapor pressure leading to self-nucleation and formation of secondary organic aerosols (SOA) as 85 multifunctional carbonyls and acids.7-9 86 87 The potential health significance of ozone-initiated terpene chemistry regarding airway effects 88 was recently reviewed.10 Generally, eye irritation-related symptoms and fatigue are among the 89 top-two reported symptoms in office environments, but nose and throat symptoms have also 90 been reported at lower prevalence.11 It is still unclear if and how ozone-initiated chemistry of 91 RVOCs may be associated with acute health outcomes.12 For instance, the BASE (Building 92 Assessment Survey and Evaluation) study including 100 public and commercial office buildings in 93 the US identified associations between late-afternoon outdoor ozone and respiratory and eye 94 irritation symptoms.13 The authors speculated whether the ozone-initiated chemistry of RVOCs 95 could be causative. 96 97 Concentrations of RVOCs and their most common oxidation products in offices have not been 98 reported on a regularly basis to our knowledge, with the exception of formaldehyde. RVOCs like 99 limonene and α-pinene from wood-based products have been measured in public buildings;14-16 100 however, data on other common RVOCs, like 3-carene, dihydromyrcenol, geraniol, linalool, and α-101 terpineol in buildings, are sparse. Concentrations of 4-oxopentanal (4-OPA) have been measured 102 ranging from 3 to 24 µg/m3 in a school, aircraft cabin and office.17-19 6-methyl- 5-heptene-2-one 103 (6-MHO) has been determined from 4 to 14 µg/m3, respectively, in offices20 and in a simulated 104 office (28.5 m3; AER = 1 h-1) with two subjects and an initial ozone concentration of 66 µg/m3;19 105 furthermore, 15-30 µg/m3 was measured in an occupied and simulated aircraft cabin with 120-140 106 µg/m3 ozone (AER = 4.4 - 8.8 h-1).18 Recently, 6-MHO was also found in commercial flights at a 107 mean concentration of 9 µg/m3.21 Measurements of the above oxidation products and three other 108 common ones from the ozonolysis of limonene, i.e. 4-acetyl-1-methyl-1-cyclohexene (4-AMCH), 3-109 isopropenyl-6-oxoheptanal (IPOH) and dihydrocarvone (DHC) have not been reported in public 110 buildings. However, simulated cleaning events in a test house and a climate chamber with the use 111 of terpene containing cleaning products have demonstrated formation of these oxidation 112 products.22,23 113 114 Within the European Union (EU) project OFFICAIR (On the reduction of health effects from 115 combined exposure to indoor air pollutants in modern offices - http://www.officair-project.eu/), 116 an intervention concerning the use of a floor cleaning agent for daily use was carried out in four 117 office buildings situated in France (FR), Greece (GR), Hungary (HU), and Italy (IT). For the 118

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intervention, a lower total VOC (TVOC) emitting cleaning agent was selected for replacement of 119 the regular floor cleaning agents in all aforementioned offices. A reference office in one building in 120 the Netherlands (NL) where cleaning was done without a floor cleaning agent also participated. 121 Thus, the objectives were: 1) To measure the concentration of common RVOCs together with 122 selected common ozone-initiated terpene oxidation products in the offices; 2) To see if the 123 replacement of the regular floor cleaning agent with a common lower TVOC emitting one would 124 change the levels of terpenes, formaldehyde, 4-AMCH, IPOH, 6-MHO, 4-OPA, and DHC; and, 3) To 125 assess whether the maximum measured concentrations could be causative of eye and airway 126 symptoms. 127 128 129 MATERIALS AND METHODS 130 131 Offices. The buildings participated on a voluntary basis and a list of criteria was used for the final 132 selection; one major criterion was “smooth flooring”. The major characteristics of the offices 133 investigated and time and date of the cleaning and the measurements are shown in Table 1. All 134 buildings were located in urban areas. They were all mechanically ventilated. The cleaning was 135 carried out by use of a terpene containing cleaning agent on a smooth flooring material, with the 136 exception of the building in NL. The cleaning schedule was maintained as usual in all buildings 137 during the entire period. The new cleaning agent (in FR, IT, GR, HU) or changes in the cleaning 138 procedure (NL) was applied for 4 weeks before and during the 2nd field campaign. In NL, however, 139 where the flooring material was a textile carpet in the offices, irregular global vacuum cleaning 140 was carried out together with a wet cloth (water) of desks. Further, a deep cleaning procedure 141 was done without the use of a cleaning agent; this included global vacuum cleaning, all surfaces 142 and objects lying on the desks had been meticulously cleaned with a wet cloth (water), all walls 143 had been dedusted. Thus, this building was considered a “reference” office, since no cleaning 144 agent was applied. 145 146 Chemicals. 4-acetyl-1-methylcyclohexene (93%), 6-methyl-5-heptene-2-one (99%), n-(+)-147 dihydrocarvone (77%) + iso (+)-dihydrocarvone (20%), dihydromyrcenol (99%), geraniol (98%), 148 limonene (99%), linalool (97%), methanol (99.8%), pentane (99.9%), α-pinene (98%), α-terpineol 149 (96%), and toluene (99.9%) were obtained from Sigma-Aldrich; acetonitrile was from ROMIL 150 (99.9%). 3-isopropenyl-6-oxoheptanal (97%) and 4-oxopentanal (97%) were synthesized according 151 to24 and25, respectively. For further details about 4-AMCH, IPOH, and 4-OPA, see.26 Tenax TA 152 (60/80) was from Supelco. 153 154 Air sampling and analysis. The field campaign was carried out following a specified protocol, once 155 one week before and once four weeks after the replacement of the regular cleaning agent. The 156 sampling was generally carried out in the center of the office at 0.9-1.2 m above floor level and at 157 least 0.5 m from other sampling stations. Office air (4.8 L) was sampled for two hours at an airflow 158 rate of 40 mL/min in duplicate on Tenax TA tubes (200 mg) in the morning (9-11h), at noon (12-159 14h), and in the afternoon (15-17h); furthermore, outdoor air was sampled once at noon. The high 160 sampling volume was necessary to achieve sufficient analytical sensitivity. A manganese dioxide or 161 KI scrubber was deliberately not applied, because of risk of VOC retention, cf.27 However, 162 degradation of the RVOCs and artefact formation of some of the oxidation products remains 163

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possible,28 see later under “Air sampling caveats”. DNPH cartridges (Waters WAT047205) were 164 sampled in duplicate at an airflow rate of 600 mL/min for two hours (72 L) without an ozone 165 scrubber for the analysis of formaldehyde. Calibrated personal pumps were used in all cases. Air 166 flow rate was checked before and after each sampling and discharged, if the difference was 167 greater than 10%. 168 169 Ozone was monitored by calibrated UV-based instruments with a time resolution of 10 sec or 1 170 min; O341M from Environnement SA (Poissy, France) in FR, Aeroqual S500 (Auckland, NZ) in GR 171 and HU, Teledyne API Model 400A (CA, USA) in NL. . All instruments had a limit of detection (LOD) 172 of 1 ppb (2 µg/m3). Data were averaged for two-hour periods, morning, noon, and afternoon, and 173 rounded to the nearest integer. Outdoor ozone was obtained from nearby monitoring stations and 174 averaged for 8 hours (08-17). Crude minimum AER values were determined on the basis of the air 175 flow rate measurements by anemometry of the fresh air intake and the dimension of the room. 176 177 Before shipment, the Tenax TA tubes were cleaned in a stream of pure nitrogen at 300 °C for 180 178 min and 340 °C for 30 min using a sample tube conditioning apparatus (TC-20, Markes 179 International, UK). Nine Tenax TA tubes in Rilsan bags were sent by courier service to the partner 180 just before the day of air sampling, then returned immediately after to NRCWE for immediate 181 thermal desorption and GC-MS analysis. Tubes were stored with Swagelok caps at ambient 182 temperature (to avoid leakage). DNPH cartridges were used as supplied and returned chilled with 183 cooling elements immediately to a designated central laboratory (CNR) and stored in the dark at 4 184 °C prior to analysis within two weeks according to LC ISO 16000-4. 185 186 The Tenax TA tubes were analyzed on a Perkin Elmer Turbo Matrix 350 thermal desorber (TD) 187 coupled to a Bruker SCION TQ GC-MS system (Bruker Daltonics, Bremen, DE). Tube desorption was 188 carried out at 275 °C for 20 min and the low and high temperatures of the cryo trap were -20 °C 189 and 280 °C, respectively. The GC column was a 30 m x 0.25 mm with 0.25 µm film thickness; VF-190 5MS (Agilent Technologies, Santa Clara, US). The oven program was as follows: 50 °C for 4 min, 191 ramp 1: 4 °C/min to 120 °C, ramp 2: 50 °C/min to 250 °C hold for 2 min. Helium (grade 6.0) was 192 used as carrier gas at an inlet pressure of 0.97 bar (1.5 mL/min). The mass spectrometer was 193 operated in SIM/Scan mode using electron ionization. Valves, transfer lines and ion source were 194 kept at 270 °C. Six-point calibration was applied (r2 > 0.99) using authentic standards in methanol 195 or pentane for 4-OPA. The quantifier ions for the calibration are shown in Table S1. The LODs, 196 based on 3xSD (Standard Deviation) (n=20) at the lowest calibration level, were in the order of 197 0.02 to 0.1 µg/m3 at 4.8 L sampling volume; exceptions were observed for 6-MHO and 4-OPA with 198 LODs of 0.3 and 3 µg/m3, respectively. Concentrations are reported as mean of duplicates and 199 rounded to the nearest integer. Comparison of concentration values from before and after the 200 intervention is based on the mean of the three measurements of the day; not detected 201 concentrations were set to ½ LOD. 202 203 Sampling recoveries for the target VOCs were determined in the laboratory as described in S1. The 204 mean recoveries were, respectively: 73% limonene; 86% α-pinene; 76% geraniol; 66% linalool; 205 93% dihydromyrcenol; 71% α-terpineol; 84% 4-AMCH; 76% IPOH; 88% 6-MHO; 88% DHC; and 86% 206 4-OPA. Geraniol and 4-OPA showed large Standard Deviations. 207 208

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The DNPH (WATERS Sep-Pak XPoSure Plus Short) cartridges were extracted with 2 mL of 209 acetonitrile for 30 min and the extract solutions were slowly filtered through a syringe filter 210 (Econofilter Agilent; d: 25 mm, pore size 0.45 µm). Solutions were analyzed by HPLC (Shimadzu 211 Corporation, Kyoto, JP) coupled with UV detection at 360 nm. The system consisted of two pumps, 212 a UV-Vis detector (SPD-M20A), an injection valve with a 20 µL loop where the solutions were 213 injected manually into an Ultra C-18 (150 mm x 4 mm, 5 µm; 100 A, Restek, IT) reversed-phase 214 column kept in an oven at 25°C. For the HPLC separation, a gradient elution program was used. 215 Initially, the gradient of the mobile phase of acetonitrile/water was set to 40/60 v/v with a linear 216 increase to 75/25 v/v within the first 15 min and hold constant up to 37.5 min, and then finally 217 decreased to 40/60 v/v. The flow rate of 1 mL/min was increased to 1.7 mL/min after 3.5 min. The 218 flow rate remained constant until 35 min, and then returned to 1 mL/min. A four-point calibration 219 (r2 = 0.999) was applied with a SD of 3.4% at the lowest calibration point, and a LOD of 0.4 µg/m3. 220 Formaldehyde concentrations are reported as the mean of duplicates and rounded to the nearest 221 integer, and after subtraction of field blank. 222 223 Air sampling caveats. The mean sampling recoveries showed degradation up to 38% for the 224 RVOCs in part in agreement with their kozone and kOH rate constants (Table S1) and previous 225 findings.28,29 The mean recoveries for the oxidation products were 76% or better. These 226 recoveries, however, should be considered as a result of a competitive ozone reactive RVOC 227 mixture, except for 4-OPA; thus, it is possible that the recovery of the RVOCs and the oxidation 228 products might be even lower, if tested as single compounds. Air sampling of formaldehyde in the 229 presence of ozone and nitrogen dioxide or low relative humidity may be problematic.30-32 Thus, 230 field sampling of formaldehyde might be underestimated.31,33 The ozone interference has typically 231 been solved by the use of an ozone scrubber; this, however, may also be associated with 232 caveats.34 Thus, a tentative sampling recovery of 85% was applied for the risk assessment of 233 formaldehyde concentration. The data for the risk assessment were corrected for the sampling 234 recoveries. 235 236 Emission test of cleaning agents. Emission test of regular and replacement cleaning agents were 237 carried out according to emission protocols for cleaning agents developed in the frame of the EU 238 EPHECT project (https://sites.vito.be/sites/ephect/). The climate chamber (0.255 m3) was made of 239 stainless steel and facilitated control of temperature (23°C ± 2°C), relative humidity (50 ± 5%), AER 240 (0.85 h-1), and air speed (0.1-0.2 m/s) according to ISO 16000-9. All products were tested, using 241 the same dilution factor recommended by the producer. The diluted products, about 1:100 242 according to the information provided, were applied (~40 mg) directly on 0.123 m2 stainless steel 243 plate and distributed with a cotton cloth. Product and cloth were weighed before and after 244 application. Air samples from the chamber were taken on Tenax TA tubes with a calibrated pump 245 and analyzed by TD-GC-MS (Agilent Technologies 5973) according to ISO 16000-2 and with an 246 average LOD of 1 µg/m3. Major RVOCs sampled after about 15 min were identified by mass 247 spectral library search and retention time. TVOC was calculated in toluene equivalents for all 248 compounds eluting after hexane and before hexadecane. 249 250 Health risk assessment. The potential exposure-effects of measured compounds were risk 251 assessed from their hazard quotient (HQ) (%). This was based on the two-hour averaged indoor air 252 concentration of the compound, corrected for its sampling recovery, divided by its air quality 253

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guideline or estimated threshold for sensory irritation or airflow limitation. Concentrations of the 254 RVOCs and target oxidation products in the participating countries were deliberately selected for 255 a simulated office with maximum levels for the assessment of acute eye and airway effects, as 256 measured either before or after the replacement. Reference values and guidelines refer to acute 257 exposure of the respective target compounds. The hazard index (HI) was calculated as the sum of 258 HQs (∑HQ) assuming normal addition of the individual HQs for sensory irritation;35 a similar mode 259 of action was assumed for airflow limitation in the airways. 260 261 262 RESULTS 263 264 The initial emission testing after 15 min of the regular cleaning agents showed limonene, except 265 IT; especially the French agent showed a concentration of 33 µg/m3. Other common VOCs and 266 RVOCs were also present (Table 2). For the selected “low TVOC emitting” cleaning agent, lower 267 concentrations of limonene, 3-carene and TVOC were observed, when compared with the other 268 cleaning products, and with exception of the Italian one. 269 270 Before the replacement of cleaning agents, the offices were characterized by limonene levels at a 271 maximum concentration up to 32 µg/m3 (5.7 ppb) in GR and 13 µg/m3 in FR; limonene levels were 272 negligible in HU and NL (Table 3). Other RVOCs were also present at lower levels; for instance, 273 dihydromyrcenol in FR, IT and HU of the order of 0.1-0.4 µg/m3; linalool concentrations were 0.1 – 274 0.6 µg/m3 in FR and HU. Furthermore, α-pinene (GR, HU) and α-terpineol (HU) were observed. The 275 behavior of limonene differed. It appeared at noon in FR and GR, but decreased later; in IT 276 limonene was present in the morning and noon, despite cleaning activities were being carried out 277 in the late afternoon. 4-OPA was present in the highest concentrations at 1, 10, and 18 µg/m3, 278 respectively, in FR, GR and IT. Notably, substantial concentrations of 4-OPA were also measured in 279 the outdoor air in FR and IT. The precursor of 4-OPA, 6-MHO was observed in all countries; the 280 highest concentrations were 7, 1, and 4 µg/m3 in GR, HU and IT, respectively. Indoor levels of 4-281 AMCH were observed in FR, IT, and NL in the range of 0.1-0.2 µg/m3; further, IPOH in GR, HU in 282 the order of 1 and 0.5 µg/m3, respectively, and trace amounts in FR. Substantial increase of 4-OPA 283 was observed in GR and IT from morning to noon (Table 3). DHC was only found in trace amounts 284 in FR. 285 286 Replacement of the regular cleaning agents with the selected low-emitting agent generally 287 resulted in lower terpene levels. Major differences are shown below for the four offices and for 288 the reference office (see Table 3). 289 290 FR: 291

• Average limonene level was about halved. 292 • Average and maximum levels of formaldehyde were more than halved. 293 • 4-AMCH, IPOH, and 4-OPA were below LOD, but some 6-MHO was seen both before and 294

after the replacement. 295 • Ozone was below LOD on both measurement days. 296

GR: 297 • Almost 10-fold lower average and maximum levels of limonene. 298

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• Average and max levels of formaldehyde were halved. 299 • α-Pinene and geraniol appeared. 300 • Substantially lower 4-OPA from average 6 µg/m3 to below LOD. 301 • IPOH and 6-MHO disappeared. 302 • Average ozone was about two-fold elevated. 303

HU: 304 • Average and maximum levels of formaldehyde were about halved. 305 • α-Pinene, dihydromyrcenol and α-terpineol disappeared. 306 • IPOH disappeared, while lower levels were observed for 6-MHO. 307 • Geraniol and 4-AMCH appeared, but also present outdoors. 308 • Average ozone level was about two-fold elevated. 309

IT: 310 • Substantially lower average level of limonene was observed together with the appearance 311

of low levels of α-pinene, geraniol and linalool. 312 • Average and maximum levels of formaldehyde were similar. 313 • Substantially lower average levels in IPOH. 314 • 6-MHO and 4-OPA were of the same order before and after, also outdoors. 315 • Average ozone was substantially higher. 316

NL (reference building): 317 • Low level of limonene appeared after the deep cleaning. 318 • No significant difference in formaldehyde. 319 • 4-AMCH and 6-MHO and some 4-OPA were observed before the deep cleaning, despite 320

the absence of limonene (and IPOH). 321 • Slightly higher level of 6-MHO. 322 • About one order of magnitude lower level of 4-OPA. 323

324 325 DISCUSSION 326 327 Despite potential underestimation of the RVOCs by the extended sampling time, the limonene and 328 formaldehyde concentrations were in line with previously reported mean values sampled over one 329 week in dwellings and public buildings.14,15 The indoor/outdoor ratios before the replacement for 330 limonene (FR, GR, IT), IPOH (GR, HU, IT), 6-MHO (GR and HU), 4-OPA (GR) were greater than 1, 331 thus indicating their indoor origin; further, linalool and α-terpineol had ratios greater than 1 in HU. 332 To our knowledge, other oxygenated RVOC concentrations have seldom been reported; however, 333 considerably higher concentrations of geraniol and linalool have been measured in Spanish homes 334 after the use of various consumer products.36 The measured values for 6-MHO are in agreement 335 with reported concentration from Tenax TA sampling in Finnish offices.20 336 337 Formaldehyde concentration was lower in line with the lower limonene levels after the 338 replacement. However, substantial concentrations of formaldehyde remained in IT, GR and HU, 339 thus indicating other sources, e.g., from ozonolysis of terpenes. For instance, personal care 340 products emitting terpenes,37 limonene emitting tea,38 the emission of formaldehyde from wood-341 based products,39 the ventilation system, even at low outdoor ozone,40,41 and from outdoor air.42 342

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A decrease of the ozone-initiated reaction products was generally achieved in all offices, except in 343 the reference office. However, for some offices other RVOCs were present of which some are 344 precursors of 4-OPA, e.g., geraniol, α-terpineol43 and linalool.44 The overall lower concentrations 345 are considered to be caused by the replacement of the cleaning agent, because the AER in the 346 offices was maintained during the two field campaigns and the daily activities were the same. 347 Furthermore, the average formaldehyde concentration in the reference office remained 348 unchanged after the deep cleaning. The overall effect of the replacement of the floor cleaning 349 agent, however, should be considered with some caution due to the possible degradation of the 350 RVOCs during the extended sampling duration, in particular for IT and GR, because of the elevated 351 ozone level and general elevated gas-phase ozonolysis of the terpenes. Despite a low limonene-352 emitting cleaning agent in IT was already in use before the replacement, substantial 353 concentrations of 6-MHO and 4-OPA were measured, thus further indicating other sources, as 354 mentioned above, in addition to infiltration from the outdoor air. Furthermore, outdoor 4-OPA 355 that is derived inter alia from ozonolysis of linalool via 6-MHO,45 was observed in IT. Generally, in 356 line with lower limonene levels, reductions of IPOH, 6-MHO and 4-OPA were observed, most 357 clearly where the limonene reduction had been substantial, e.g., in GR. 358 359 An additional major route, e.g., considerably higher reaction probability than gas-phase 360 ozonolysis, to both 6-MHO and 4-OPA, is surface oxidation reactions of deposited RVOCs46,47 and 361 reaction of skin debris, e.g. squalene48 and unsaturated fatty acids.49 For instance, Weschler and 362 Wisthaler19 concluded that more than 90% of gaseous 4-OPA was generated through surface 363 reactions. This may be in line with the substantial reduction of 4-OPA after the extensive deep 364 cleaning of all surfaces in the reference office. The deep cleaning may have removed skin debris 365 and soiled textile fibers from the carpet surfaces, e.g., hair50 and clothing.19,51 The surface reaction 366 probability depends on a number of factors, e.g., humidity, porosity and oily surface films.46,52 367 Another source of 4-OPA is ozone exposed ventilation filters; for instance, a downstream 4-OPA 368 concentration of 41 µg/m3 (10 ppb) has been reported.40 Furthermore, ozonolysis of sampled 6-369 MHO on Tenax TA to 4-OPA cannot be ruled out, since some loss of 6-MHO was observed in the 370 recovery study. 371 372 The presence of ozone in part governed the formation of the oxidation products. For instance, a 373 high content limonene cleaning agent before the replacement was used in FR, but the 374 concentration of the oxidation products was low in agreement with the absence of ozone, as 375 opposed to GR, where both 6-MHO and 4-OPA were present at relatively high levels in agreement 376 with the elevated level of ozone. 377 378 Mechanistic gas-phase model work mimicking a high ozone (50 ppb; 100 µg/m3) cleaning 379 simulation for 30 min with a maximum limonene concentration of 160 ppb (891 µg/m3) in a typical 380 residential environment (cf.53) resulted in total average concentrations of formaldehyde, 4-AMCH 381 and IPOH of 41, 23 and 13 µg/m3, respectively.54 These levels are slightly above those measured in 382 this study; the levels approach the modeled ones, if corrected for their sampling recoveries. 4-OPA 383 was negligible in contrast to our measurements, thus, indicating that this compound has other 384 sources as described above. The same four compounds were modeled in European offices during 385 extreme conditions at low/high AER and cleaning vs no cleaning in the morning or late afternoon 386 by use of a detailed indoor air chemistry model using limonene, only.55 Higher average 387

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concentrations of formaldehyde, 4-AMCH and IPOH were observed by late afternoon cleaning 388 (relative to morning cleaning) at 19, 17 and 39 µg/m3, respectively, at 1.5 AER and 27 ppb (54 389 µg/m3) indoor ozone. These levels are slightly above in comparison to those found in this study, 390 especially regarding 4-AMCH, which only appeared in HU. Again, 4-OPA was insignificant in the 391 model work as opposed to the measured levels in this study. However, cleaning in the morning at 392 4.7 ppb (9 µg/m3) ozone resulted in 8, 2.5 and 8 µg/m3 of formaldehyde, 4-AMCH, and IPOH, 393 respectively; modeled levels that are more in line with the measured concentrations. However, 394 inter alia, the time of cleaning, the overall reactive surface, and the AER are also critical factors to 395 be considered. Furthermore, the model did not incorporate other RVOCs and surface reactions. 396 397 The maximum measured and corrected concentrations are shown with their associated health 398 thresholds for acute airway effectsHQ for sensory irritation and airflow limitation in Table 4. The 399 HIs in a simulated office with all maximum concentrations (either before or after the replacement) 400 for sensory irritation by formaldehyde, IPOH and 6-MHO and airflow irritation by DHC, 4-AMCH 401 and 4-OPA were 25% and 21%, respectively. Thus, it is less likely that the contribution of these 402 target compounds can explain eye sensory irritation, which is among the most important 403 symptoms reported in office environments.11 Other occupational, environmental, and personal 404 risk factors should be considered and assessed for reported ocular symptoms,56,57 because office 405 VOCs generally have thresholds for sensory irritation that are two-three orders of magnitude 406 higher11,58 than their measured indoor concentrations.13,58,59 The exposure to outdoor pollutans 407 from traffic during commuting to work may also deteriorate the ocular surface stability;60 thus, the 408 eyes may be come susceptible prior to start of office work. Since the concentrations for this risk 409 assessment represent two-hour averages, temporary elevated levels, which are activity 410 dependent, may occur; however, these levels are not considered to be causative of sensory eye or 411 airway irritation, even by a two-fold increase.11 Furthermore, the threshold for formaldehyde 412 induced eye irritation is considered to be higher than 0.1 mg/m3 according to WHO (2010).61-62 413 Although, the impact of 4-OPA is limited on airflow limitation, caution, however, must be taken 414 due to its large SD and many potential sources. 415 416 To our knowledge, this is the first time common fragrance terpenes and their ozone-initiated 417 terpene reaction products have been measured in offices, and furthermore, risk assessed for 418 common acute symptoms in offices concurrent with the replacement of the regular cleaning 419 agents to one agent with lower TVOC emission. This replacement is believed to cause a reduction 420 in both limonene and formaldehyde, despite potential sampling caveats. Reduction in ozone-421 initiated terpene reaction products, such as 4-OPA, was observed, but not in all countries, thus 422 indicating other sources than limonene, e.g., the reaction of other RVOCs, including surface 423 oxidation reactions of RVOCs and skin debris. Thus, deep cleaning of all surfaces including the 424 textile floor reduced the 4-OPA concentration. The concentrations of formaldehyde, IPOH, 4-425 AMCH were within the same order of magnitude to those modeled in a simulated late-afternoon 426 cleaning event with limonene in offices; however, the gas-phase modeling does not encounter 427 surface reactions which may be the major source of 6-MHO and 4-OPA, and other RVOC sources. 428 The maximum concentrations in the simulated office appear not to be a direct cause of the high 429 prevalence of eye irritation-related symptoms often encountered in office buildings; however, in 430 view of the low number of offices investigated, a larger field campaign is warranted for 431

11

confirmation. 4-OPA may call for further improvement of air sampling and analysis for 432 optimization of ideal sampling conditions at elevated ozone levels for future field campaigns. 433 434 435 AUTHOR INFORMATION 436 Corresponding author 437 E-mail: pwo@nrcwe.dk; phone: +45 39165272; fax: +45 39165201: mail: Lersø Parkallé 105, DK-438 2100 Copenhagen Ø, Denmark 439 440 Author contributions 441 The manuscript was written through contribution from all authors. All authors have approved the 442 manuscript. 443 444 Notes 445 The authors declare no competing financial interest. 446 447 448 ACKNOWLEDGEMENTS 449 450 This work was supported by the project “OFFICAIR” (On the reduction of health effects from 451 combined exposure to indoor air pollutants in modern offices) funded by the European Union 7th 452 Framework (Agreement 265267) under the Theme: ENV.2010.1.2.2-1. We thank the respective 453 facility managements for their permission to carry out measurements in the offices. We are also 454 grateful to their assistance in the field campaigns: D. Campagnolo (Italy), S. Ritoux and G. Fiegel 455 (France), E. de Oliveira Fernandes (Portugal). Excellent technical assistance by B. Hansen (DK) is 456 gratefully acknowledged. 457 458 459 SUPPORTING INFORMATION AVAILABLE 460 Recovery study information, target ions, recoveries, ozone and OH radicals rate constants for 461 target compounds. This information is available free of charge via the Internet at 462 hhtp://pubs.acs.org/. 463 464 465 REFERENCES 466 (1) Zock J. P.; Vizcaya D.; Le Moual N. Update on asthma and cleaners. Curr. Opin. Allergy Clin. 467

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17

Table 1. Characteristics of the offices before and after replacement of cleaning agent. 684 France Greece Hungary Italy The Netherlands Cleaning schedule Time of day

Every day Late afternoon

Twice a week Late afternoon

Every day Mid-morning

Every day Late afternoon

Deep cleaning

Late afternoon City Paris Athens Budapest Florence Delft Date of air sampling: Before After

10/01/2014 12/02/2014

07/02/2013 10/04/2013

07/05/2013 11/06/2013

12/03/2013 16/04/2013

10/04/2013 15/05/2013

Type of building/floors Public agency/4 Commercial/2 University/8 Bank- back-office/3 Office building/7 Type of floor Synthetic smooth Synthetic (wood) Synthetic smooth Stone/ceramic Carpet (textile) Activity in room VDUa work/paperwork VDU work/paper work

VDU work/paper work VDU work/paper work Meeting room

Location of sampling 4th floor 2nd floor Ground floor 2nd floor 3rd floor Volume of office, m3 61 255 63 927 29 Mechanical ventilation (supply and exhaust) Air exchange rate, h-1

Yes

1.4

Yes

1.3 - 1.4

Yes

Min 3.2

Yes

1.1 - 0.9

Yes

4 Average number of people in office

2 15 4 10 2-3 twice per day for 1-2 hrs

Location, center/suburban Green area around

City center Few small areas around

Suburban No

Urban area 50 m from River Danube

Commercial//residential No

Suburban

Traffic density Heavy, 20 m to the ring highway around Paris.

Air sampling room was on the opposite

Light, but close to the national highway

Light (within 50 m) Light

Light

Humidity (average 9-17), % Before After

29.5 ± 0.5 27.3 ± 0.7

40.1 ± 2.1 36.8 ± 2.6

50.9 ± 0.8 53.3 ± 1.9

39.6 ± 5.2 37.5 ± 0.7

26.3 ± 2.4 26.4 ± 0.5

Temperature (average 9-17), °C Before After

23.2 ± 0.2 22.1 ± 0.3

26.6 ± 1.1 25.3 ± 0.7

26.7 ± 0.4 25.1 ± 0.1

24.8 ± 0.8 25.1 ± 1.1

25.7 ± 0.6 25.5 ± 0.5

Use of air freshener No No No No No Plants/flowers in office No No Yes (2) No No Photocopier or laser printer in the office

No No

One laser printer 6 laser printers

No

Window opening Before After

No No

Early in the morning Early in the morning

Semi-open all day Semi-open all day

Semi-closed (11-17) Semi-open (11-17)

No No

a) Visual display unit. 685 686

18

Table 2. Major reactive volatile organic compounds (RVOCs) and total organic compounds (TVOCs) emitted from regular cleaning agents 687 used before and the new one after intervention. Concentrations (µg/m3) in a 0.255 m3 climate chamber 15 min after the application of 688 the diluted cleaning agent (ca. 40 mg on a 0.123 m2 stainless steel plate). 689 Limonene α-

Pinene 3-

Carene Linalool Dihydro-

myrcenol Other RVOCs (µg/m3) Other compounds TVOCa

France 33 - - 14 5 10-undecenal (5) 4-(2,6,6-trimethyl-2-cyclohexen-1-

yl)-3-penten-2-one (38) 1-(2,6,6-trimethyl-2-cyclohexen-1-

yl)-1-penten-3-one (10)

Aldehydes, aromatic hydrocarbons, glycol ethers,

phenyl ethanol

395

Greece 6 1 - - 17 Styrene (2) Aromatic hydrocarbons, glycol ethers, benzaldehyde,

camphor, decanal

151

Hungary 4 1 - - - Propenoic acid, 3-(2-thienyl)-2,6-dichlorophenyl ester (3)

Aromatic hydrocarbons, esters

93

Italy - - - 3 - Aromatic hydrocarbons, aldehydes, esters

32

Replacement product

9 - 2 - - Aliphatic alcohols, aldehydes, 2-phenoxyethanol, 5-methyl-

2-(1-isopropyl)-1-hexanol

56

-) Below limit of detection; a) Toluene equivalents. 690 691

692

693

19

Table 3. 2-hour average concentrations (µg/m3) of terpenes, oxidation products, formaldehyde, 694 and ozone (8-hour) in offices, before and after replacement of cleaning agent or deep cleaning. 695

FR Limonene α-Pinene Geraniol Linalool Dihydro myrcenol

α-Terpineol

4-AMCH

Dihydro carvone IPOH 6-MHO 4-OPA CH2O O3

Before Morning 1.0

n.d.

n.d.

0.4 0.2

n.d.

n.d.

n.d.

n.d. n.d. n.d. 7.5

n.d.

Noon 13 0.2 0.1 n.d. n.d. n.d. 7

Afternoon 6 0.1 0.1 n.d. n.d. n.d. 7

Outdoor 1.4 n.d. n.d. 0.1 2 11 n.m. 26a

After Morning 1.2

n.d.

n.d.

0.2 0.2

n.d.

n.d.

n.d.

n.d.

0.5

n.d.

3.5

n.d.

Noon 1.4 0.1 n.d. 0.4 2

Afternoon 0.5 0.1 n.d. 0.5 1

Outdoor n.d. n.d. n.d. n.d. n.m. 39a

n.d. = below LOD; n.m. = not measured. a) Mean concentration from nearest monitoring station. 696 697 698

GR Limonene α-Pinene Geraniol Linalool Dihydro myrcenol

α-Terpineol 4-AMCH Dihydro

carvone IPOH 6-MHO 4-OPA CH2O O3

Before Morning n.d. 0.2

n.d. n.d. n.d. n.d. n.d. n.d.

0.1 n.d. 5 8.5 4

Noon 32 0.1 1.3 7 10 16 7

Afternoon n.d. 0.1 0.3 1.3 3 20 11

Outdoor n.d. n.d. n.d. n.d. n.d. 2.5 71a

After Morning 2 1.2 1.4

n.d. n.d.

n.d.

n.d. n.d. n.d. n.d. n.d.

2.5 5

Noon 1.0 0.6 0.6 0.1 10 19

Afternoon 0.6 0.7 n.d. n.d. 9.5 15

Outdoor n.d. 1.0 0.6 n.d. 2 70a

n.d. = below LOD; n.m. = not measured. a) Mean concentration from nearest monitoring station. 699 700

20

701

HU Limonene α-Pinene Geraniol Linalool Dihydro myrcenol

α-Terpineol 4-AMCH Dihydro

carvone IPOH 6-MHO 4-OPA CH2O O3

Before Morning n.d. 0.1

n.d.

0.4 0.4 0.3

n.d. n.d.

0.2 1

n.d.

11.5 3.5

Noon 0.1 0.3 0.6 0.4 0.3 0.5 1.1 16 4

Afternoon 0.1 0.2 0.2 0.3 0.1 0.4 1.2 10.5 4

Outdoor n.d. n.d. 0.1 0.2 n.d. 0.1 n.d. n.m. 31a

After Morning 0.1

n.d.

1.0 0.4

n.d.

n.d.

1.0

n.d. n.d.

0.7

n.d.

8 8

Noon 0.1 0.5 0.2 0.9 0.7 4.5 9

Afternoon n.d. 0.4 0.1 0.9 0.7 5 8

Outdoor n.d. 0.5 0.1 0.9 0.4 n.m. 56a

n.d. = below LOD; n.m. = not measured. a) Mean concentration from nearest monitoring station. 702 703 704 705

IT Limonene α-Pinene Geraniol Linalool Dihydro myrcenol

α-Terpineol 4-AMCH Dihydro

carvone IPOH 6-MHO 4-OPA CH2O O3

Before

Morning 2

n.d. n.d. n.d.

0.3

n.d.

0.1

n.d.

11 2 7 10 0

Noon 9 n.d. 0.1 10 4 18 13 1.5

Afternoon n.d. n.d. n.d. 4 3 16 11 0

Outdoor n.d. n.d. n.d. n.d. n.d. 8 n.m. 74a

After

Morning 1.5 0.2 1.2 0.2

n.d. n.d. n.d. n.d.

n.d. 2 5a 8 13

Noon 1.7 0.2 1.2 0.4 0.4 2 8a* 10 8

Afternoon 0.3 n.d. n.d. 0.3 0.1 n.d. n.d. 7 37

Outdoor 1.2 0.3 1.3 0.5 0.4 n.d. 12a n.m. 99a

n.d. = below LOD. n.m. = not measured. a) Large uncertainty, since one tube showed 4-OPA below LOD. b) Mean concentration from nearest monitoring station. 706 707 708

709 710 711 712 713 714 715 716 717

21

NLa Limonene α-Pinene Geraniol Linalool Dihydro myrcenol

α-Terpineol 4-AMCH Dihydro

carvone IPOH 6-MHO 4-OPA CH2O O3

Before

Morning

n.d. n.d. n.d. n.d. n.d. n.d.

0.2

n.d. n.d.

0.3 3 8 3.5

Noon 0.2 n.d. 4 10 9

Afternoon 0.2 n.d. 4 7 16.5

Outdoor 0.2 n.d. n.d. n.m. 40b

After

Morning 0.2

n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

1.5 n.d. 6 16

Noon 0.3 0.5 n.d. 8 19

Afternoon 0.4 n.d. n.d. 5 23.5

Outdoor 0.3 n.d. n.d. n.m. 66b

a) No use of floor cleaning agent, but with deep cleaning after. b) Mean concentration from nearest monitoring station. n.d. = below LOD; n.m. = not measured. 718 n.m. = not measured. 719 720 721

22

Table 4. Two-hour averaged maximum indoor concentrations of terpenes, 722 ozone-initiated terpene reaction products, and ozone measured in European 723 offices, comparison with reference or guideline values for eye and airway effects, 724 and hazard index as sum of hazard quotions (HQs). 725 Compound Reference Threshold

µg/m3

Max. conc.

µg/m3

Corrected max. conc.e

µg/m3

CountryF HQ

%

Formaldehyde (0.5 h)a

61 100 20 24 GR-B 24

Ozone (8 h)b 63 100 37 37 IT-A 37 Limonenea 11 8500 38 52 GR-A 0.6 α-Pinenea 11 14000 1 1 GR-A - Geraniola ~8500d 1.4 2 GR-A - Linaloola ~8500d 0.6 1 HU-B - Dihydromyrcenola ¨8500d 0.4 0.4 HU-B - α-Terpineola ~8500d 0.3 0.4 HU-B - 4-AMCHc 26 1130 1 1 HU-A 0.08 Dihydrocarvonec 26 4980 <0.1 < 0.1 FR-B - IPOHa 26 1100 11 14 IT-B 1 6-MHOa 26 1550 7 8 GR-B 0.5 4-OPAc 26 123 18 21 IT-B 21 Hazard index, ∑HQs %, SI 25 Hazard index, ∑HQs %, AFL 21 a) Sensory irritation (SI), acute effect. b) Pulmonary irritant. c) Airflow limitation (AFL), long-term effect. 726 d) Assumed to be in the same order of magnitude as limonene. e) Corrected for mean sampling recovery. 727 f) A= after intervention; B=before intervention. - = Negligible. 728 729

23

730 Supporting Information 731

732 733

Ozone-initiated Terpene Reaction Products in Five European Offices: 734 Replacement of a Floor Cleaning Agent 735

736 A.W. Nørgaard,§ V. Kofoed-Sørensen,§ C. Mandin,# G. Ventura,¤ R. Mabilia,¶ E. Perreca,¶ A. 737 Cattaneo,‖ A. Spinazzè, ‖ V.G. Mihucz, † T. Szigeti, † Y. de Kluizenaar,∋ H.J.M. Cornelissen,∋ M. 738 Trantallidi,ψ P. Carrer,ψ I. Sakellaris,φ J. Bartzis,φ and P. Wolkoff,§,* 739 740 §National Research Centre for the Working Environment, 2100 Copenhagen Ø, Denmark 741 #Université Paris-Est, Centre scientifique et technique du bâtiment, 77447 Marne La Vallee Cedex 742 2, France 743 ¤IDMEC, University of Porto, 4200-465 Porto, Portugal 744 ¶CNR Institute for Atmospheric Pollution Research, Roma 1, Montelibretti, Italy 745 ‖‖Dept of Science and High Technology, University of Insubria, 22100 Como, Italy 746 †Cooperative Research Centre for Environmental Sciences, Eötvös Loránd University, H-1117 747 Budapest, Hungary 748 ∋The Netherlands Organization for Applied Scientific Research (TNO), 2600 AA Delft, The 749 Netherlands 750 ψ Dept of Biomedical and Clinical Sciences - Hospital L. Sacco, University of Milan, 20157 Milan, 751 Italy 752 φDept of Mechanical Engineering, University of West Macedonia, Kozani, West Macedonia, T. K. 753 50100, Greece 754 755

756

24

Sampling recoveries: Sampling recoveries for the target VOCs were determined by spiking 10 757 Tenax TA tubes with a mixture in methanol of 30 ng of each RVOC standard, except for 4-OPA; five 758 tubes were desorbed immediately after purging with helium as for calibration and five tubes were 759 exposed simultaneously to 5.0 L ambient laboratory air for two hours by use of calibrated pumps 760 (Chematec, DK). Two conditions were tested, one at 20-40 µg/m3 ozone and one at 60-70 µg/m3 761 ozone (windows open), respectively, at 25-26°C. Back-up tubes were coupled downstream to the 762 spiked tubes for possible break-through; further, five unspiked tubes were sampled for 763 background correction of the laboratory air. 4-OPA (132 ng/m3) in pentane was spiked on 10 764 separate tubes. The sampling recoveries were determined as a percentage (%) of the non-exposed 765 spiked tubes by comparison of the peak areas of the corresponding quantifier ions of the 766 compounds. The concentration of ambient ozone was measured continuously by a Teledyne API 767 265A (CA, USA). 768

769

Table S1. Quantifier ions for calibration, recoveries (%) and standard deviations (n=5) of spiked 770 terpenes and terpene oxidation products on Tenax TA after 4.8 L ambient air sampling for two 771 hours, respectively, and their ozone and OH rate constants. 772

Sampled compounds Quan-tifier ion

m/z

Recovery ± SD

%

Mean recovery

%

kO3+terpene rate constant x10-18

cm3molecule-1s-1

kOH+terpene rate constant x10-10

cm3molecule-1s-1

Ref.

Ozone µg/m3 20-40 60-70

Linalool 93 62 ± 3 70 ± 2 66 430 1.6 1 6-methyl-5-heptene-2-one (6-MHO)

108 86 ± 6 89 ± 8 88 ≤414 - 2

α-Terpineol 59 68 ± 5 74 ± 7 71 300 1.9 3 Limonene 67 67 ± 3 79 ± 2 73 210 1.7 4

5 4-Acetyl-1-methylcyclohexene (4-AMCH)

95 79 ± 21 89 ± 3 84 150 1.3 6

α-Pinene 93 86 ± 2 85 ± 1 86 87 0.55 4 5

3-isopropenyl-6-oxoheptanal (IPOH)

107 60 ± 5 92 ± 9 76 8 1.1 7

Dihydromyrcenol 59 94 ± 6 92 ± 2 93 2 0.4 8 Geraniol 69 60 ± 14 92 ± 24 76 930 2.3 9 Dihydrocarvone 67 84 ± 3 92 ± 2 88 - - 4-Oxopentanal 72 86 ± 40 n.m. 86 Not relevant Not relevant n.m. = Not measured. - = Not found. 773

774

775

776

25

References 777

(1) Atkinson R.; Arey J.; Aschmann S. M.; Corchnoy S. B.; Shu Y. Rate constants for the gas-phase 778 reactions of cis-3-hexen-1-ol, cis-3-hexenylacetate, trans-2-hexenal, and linalool with OH and NO3 779 radicals at 296±2 K, and OH radical formation yields from the O3 reactions. Int J Chem Kinet 1995, 780 27, 941-955. 781

(2) Grosjean E.; Grosjean D.; Seinfeld J. H. Gas-phase reaction of ozone with trans-2-hexenal, trans-2-782 hexenyl acetate, ethylvinyl ketone, and 6-methyl-5-heptene-2-one. Int J Chem Kinet 1996, 28, 373-783 382. 784

(3) Wells J. R. Gas-phase chemistry of α-terpineol with ozone and OH radical: Rate constants and 785 products. Environmental Science & Technology 2005, 39, 6937-6943. 786

(4) Atkinson R.; Hasegawa D.; Aschmann S. M. Rate constants for the gas-phase reactions of O3 with a 787 series of monoterpenes and related compounds at 296 ± 2 K. International Journal of Chemical 788 Kinetics 1990, 22, 871-888. 789

(5) Atkinson R.; Aschmann S. M.; Pitts Jr J. N. Rate constants for the gas-phase reactions of the OH 790 radical with a series of monoterpenes at 294 ± 1 K. Int J Chem Kinet 1986, 18, 287-299. 791

(6) Atkinson R.; Aschmann S. M. Atmospheric chemistry of the monoterpene reaction products 792 nopinone,camphenilone, and 4-acetyl-1-methylcyclohexene. J Atmos Chem 1993, 16, 337-348. 793

(7) Calogirou A.; Jensen N. R.; Nielsen C. J.; Kotzias D.; Hjorth J. Gas-phase reactions of nopinone, 3-794 isopropenyl-6-oxo-heptanal, and 5-methyl-5-vinyltetrahydrofuran-2-ol with OH,NO3,and ozone. 795 Environ Sci Technol 1999, 33, 453-460. 796

(8) Forester C. D.; Ham J. E.; Wells J. R. Gas-phase chemistry of dihydromyrcenol with ozone and OH 797 radical: Rate constants and products. Int J Chem Kinet 2006, 38, 451-463. 798

(9) Forester C. D.; Ham J. E.; Wells J. R. Geraniol (2,6-dimethyl-2,6-2,6-diene-8-ol) reactions with ozone 799 and OH radical: Rate constants and gas-phase products. Atmos Environ 2007, 41, 1188-1199. 800

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