Environ. Eng. Res. Vol. 12, No. 2, pp. 72～80, 2007 Korean Society of Environmental Engineers

ULTRA-FINE PARTICLES AND GASEOUS VOLATILE ORGANIC COMPOUND EXPOSURES FROM THE REACTION OF AND CAR-AIR FRESHENER DURING METROPOLIS TRAVEL

Rheo B. Lamorena1, Su-Mi Park2, Gwi-Nam Bae2, and Woojin Lee1,† 1Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, 373-1 Daejon, Korea 2Environment and Process Technology, Korea Institute of Science and Technology, 130-650 Seoul, Korea (received June 2007, accepted May 2007)

Abstract：Experiments were conducted to identify the emissions from the car air freshener and to identify the formation of ultra-fine particles and secondary gaseous compounds during the ozone-initiated oxidations with emitted VOCs. The identified primary constituents emitted from the car air freshener in this study were -pinene,  -pinene, -cymene and . Formation of ultra-fine particles (4.4 - 160 nm) was observed when ozone was injected into the chamber containing emitted monoterpenes from the air freshener. Particle number concentrations, particle mass concentrations, and surface concentrations were measured in time dependent experiments to describe the particle formation and growth within the chamber. The irritating secondary gaseous products formed during the ozone-initiated reactions include , , acrolein, , and propionaldehyde. Ozone concentration (50 and 100 ppb) and temperature (30 and 40 °C) significantly affect the formation of particles and gaseous products during the ozone-initiated reactions. The results obtained in this study provided an insight on the potential exposure of particles and irritating secondary products formed during the ozone-initiated reaction to passengers in confined spaces.

Key Words：Ozone, Volatile organic compounds, Monoterpenes, Particles, Air freshener

INTRODUCTION1 ozone can be easily introduced into indoor environments and confined spaces by opening 1) The atmospheric oxidants (e.g., O3, ․OH, windows and operating ventilation systems.

NO3)–initiated reactions with volatile organic Regulations for the restriction of toxic VOCs compounds (VOCs) emitted from biogenic sou- emission in indoor environments and confined rces (e.g., vegetation, trees, etc.) significantly spaces have recommended manufacturers to uti- affect outdoor air environments. Ozone, one of lize environment-friendly natural products for the significant atmospheric oxidants, frequently their raw materials as alternatives to the toxic exceeds the maximum threshold ambient level anthropogenic chemicals such as xylene and all the year round in many countries. Ambient . As an example, car air freshener con- tains the natural products such as extracts from

† essential oil and plant oil commonly found in Corresponding author 2,3) E-mail: [email protected] scenting agents and , which could be Tel: +82-42-869-3624, Fax: +82-42-869-3610 Ultra-Fine Particles and Gaseous Volatile Organic Compound Exposures from the Reaction of Ozone and Car-Air Freshener During Metropolis Travel 73 a potential source of biogenic VOCs in a con- cularly significant during hot and sunny days. fined space (i.e., inside of the car). It is well The health of passengers inside the vehicles known that biogenic VOCs such as monoter- could be affected by these organic secondary penes have an exceptional capacity to generate products formed during the ozone-initiated oxida- condensable products as a result of oxidation tion with biogenic VOCs emitted from car air with ozone in early stage. The ozone-initiated freshener. We have investigated the effects of oxidation subsequently forms ultra-fine particles temperature as well as the ozone concentration and potentially irritating gaseous organic products on the formation of secondary organic products such as formaldehyde, , hydro- inside the vehicle during hot summer season in xyl radicals, and other low volatile oxygenated this research. Target biogenic VOCs emitted compounds.4-7) It has been reported that ultra- from the car air freshener and all gaseous pro- fine (less than 100 nm) and fine (less than 1000 ducts and particles have been monitored and nm) particles can be produced during the oxida- identified during the ozone-initiated reactions. tion of with ozone. They are mostly in the range of 67 - 397 nm, which is very appro- MATERIALS AND METHODS priate for the deposition in respiratory tracts. Therefore, they can easily cause harmful effects Chemicals 8,9) (e.g., irritations) on human and animals. The The car air freshener was purchased from an ultra-fine particles have a high alveolar deposi- internet-based store in Seoul, Korea. It was an tion fraction and larger surface area, which could oil-based and a citrus scented air freshener. The increase the possibility to react with a living air freshener was received in a glass container body and/or to play a role as the carrier of toxic and the amount of emission could be controlled 10,11) gas. The ambient ozone concentration could by adjusting the cover. It was chosen to best be high enough to initiate chemical oxidations represent the source and ozone was used with monoterpenes emitted from car air fresh- as a representative atmospheric oxidant in con- ener so that the use of car air freshener under fined environments. The air freshener does not the condition can lead to the exposure and/or necessarily represent all different types of car air inhalation of toxic ultra-fine particles and secon- fresheners. dary gaseous organic products. However, no sig- The chemicals used for the analyses of target nificant study has been conducted to characterize compounds and products were ACS grade or the ozone-initiated oxidation with biogenic VOCs higher: -pinene (98%, Sigma-Aldrich), -pinene emitted from car air freshener during driving a (99%, Sigma-Aldrich), limonene (97%, Sigma- car. Aldrich), p-cymene (99%, Sigma-Aldrich); the Smog chamber studies have shown that tem- carbonyl standard mixture (formaldehyde: 215 perature significantly affects the distribution of µg/mL, acetaldehyde: 190 µg/mL, acetone/acrolein: secondary gaseous products and particles. The 122 µg/mL, and propionaldehyde: 122 µg/mL, reaction kinetic rate increased as the temperature Supelco). The solvents used as eluents and increased producing volatile or high condensable extractants in this research were HPLC or higher gases. The vapor pressures of organic compounds grade: acetonitrile (99.8%, J.T. Baker) and pure increases as well yielding a lower fraction of water (J.T. Baker). condensable gases.12,13) It has been shown that the increase of temperature considerably affects Experimental Procedures the gas-particle equilibrium and favors the for- A Teflon® film batch bag (~5 L) was used to mations of high concentrations of gas-phase identify the biogenic VOCs emitted from the car products and low concentrations of particle-phase air freshener. A Teflon® film chamber (1 m3) products.14) Outdoor ground-level ozone is parti- was used to investigate and monitor the effects

VOL. 12, NO. 2, 2007 / ENVIRONMENTAL ENGINEERING RESEARCH 74 Rheo B. Lamorena, Su-Mi Park, Gwi-Nam Bae, and Woojin Lee of ozone concentrations and temperature on the experimental run. formation of secondary products such as alde- Identification and quantification of the mono- hydes and ketones and ultra-fine particles. The terpenes were determined using Fourier transform schematic diagram of experimental setup used infrared spectrometer (FT/IR, Model 1400-1F, for the chamber experiments is shown in Figure 1. MIDAC) and a gas chromatograph with mass Ozone was produced in-situ using an ozone spectrometer (GC-MS, Varian Model Saturn 2000) generator equipped with an ultraviolet lamp equipped with a DB-1 column (60 m × 0.32 mm (Advanced Pollution Instrumentation) and a flow i.d. × 1.8 µm film thickness, J&W Scientific). meter. The concentration of ozone was monitored The carbonyl samples in the chamber were col- during the reactions with monoterpenes using a lected before ozone addition and during the ozone- photometric ozone analyzer (Thermo Environmental initiated reactions using 2,4-dinitrophenylhydrazine Instruments Inc.) at a wavelength of 254 nm. coated cartridges (Supelco) for 10 min under the An aliquot amount of liquid air freshener (0.5 flow rate of 0.6 L/min. Carbonyl compounds in mL) was placed in the bottom of 50 mL beaker. the atmosphere were adsorbed in the cartridge It was allowed to emit the biogenic VOCs for 1 during the sampling and then eluted by adding 5 hour inside the chamber bag. The temperature mL of acetonitrile. An aliquot of extractant (20 was controlled at 30°C and 40°C. Ozone was μL) was introduced into the injection port of a injected at two different concentrations (50 and high performance liquid chromatograph (HPLC, 100 ppb) with a flow rate of 2.0 L/min at each Waters 600S, Waters) equipped with an ultravio- temperature. The total reaction time was appro- let (UV) detector and Nova-Pak C18 column (3.9 ximately 4 hours, which is slightly more than mm × 300 mm, Waters). the average travel time in a metropolitan area. Particle number concentrations were monitored The chamber was flushed with ozone and puri- by a scanning mobility particle sizer (SMPS, TSI fied air for several hours before and after each 3085) and an ultra-fine condensation particle cou-

Figure 1. Schematic diagram of Teflon® film chamber.

ENVIRONMENTAL ENGINEERING RESEARCH / VOL. 12, NO. 2, 2007 Ultra-Fine Particles and Gaseous Volatile Organic Compound Exposures from the Reaction of Ozone and Car-Air Freshener During Metropolis Travel 75 nter (UCPC, TSI 3025). The total particle num- produced during the ozone-initiated oxidations ber concentrations for diameters larger than 3 nm with monoterpenes.15) The particles have been were measured with the UCPC, while the parti- known to form from a self-nucleation process cle number size distributions from 4.4 nm to 160 with the subsequent condensation of new parti- nm were measured with the SMPS. The particles cles and/or from a thermodynamic equilibrium are assumed to have a sphere shape with a par- distribution between the gas and particle phases ticle density of 1.0 g/cm3. The human lung-depo- leading to the gas-particle partitioning of semi- sited surface area of particle was measured by a volatile organic compounds (SVOCs).16) The for- nano-particle surface monitor (Model 3550, TSI). mation and growth of particles from the reactions The measured surface area corresponds to trache- of ozone with the emitted terpenes from the car obronchial and alveolar regions of the human lung. air freshener have been observed. In the ozone- initiated oxidations with air freshener, rapid par- RESULTS AND DISCUSSION ticle production was observed in 15 min. Figure 3 shows the change of particle number concent- Identification of Biogenic VOCs Emitted ration at 30°C under 50 and 100 ppb of ozone fro m Car A ir Freshener measured by UCPC. Nucleation started earlier at The biogenic VOCs identified from the emis- high concentration of ozone (100 ppb) suggesting sion of liquid car air freshener were monoter- that ozone concentration significantly affects the penes including -pinene (0.046 ppm), -pinene nucleation rate of particle formation. This is very (0.023 ppm), -cymene (0.001 ppm), and limo- similar to the result observed from the ozone- nene (0.005 ppm). Air (carbon dioxide and initiated oxidation with biogenic VOCs emitted 17) nitrogen) was identified, which are mainly due from natural paint. The observed time delay to the contamination by impurities during the for the nucleation at low concentration indicates analysis. The chromatogram in Figure 2 confirmed the time needed to reach the supersaturation that the biogenic VOCs emitted from the air points. After reaching the supersaturation point, freshener were mainly composed of the four mono- the concentrations of semi-volatile products star- terpenes identified above. ted to increase to sufficient levels to form par- ticles or to condense on the pre-existing smaller particles. The peak number particle concentra- tions at two ozone concentrations were almost similar: 1.7 × 104 cm-3 at 50 ppb and 1.67 × 104 cm-3 at 100 ppb ozone.

Figure 2. GC/MS chromatogram of biogenic VOCs emitted from car air freshener.

Effect of Ozone Concentration on the Par- Figure 3. Particle number concentrations observed ticle Formation at 30°C with ozone concentrations at 50 It has been reported that particles can be ppb and 100 ppb measured by UCPC.

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After the particle number concentrations have 20 nm diameter is very appropriate for alveolar reached the maximum peak, it gradually decreased deposition in the human lung. It has been further as the particles undergo condensation mechanisms investigated that deposited ultra-fine particles are and are deposited on chamber walls. The parti- rendered less available during phagocytosis by cle number concentration at the high ozone con- alveolar macrophages. Thus, they are not phago- centration decreased slowly, suggesting that more cytosized efficiently and may be easily transpor- particles are being formed during the condensation ted to other organs of the body.10,11) Figure 5 stage. Figure 4 shows the change of the particle shows the human lung-deposited surface area by number concentration as well as particle mass particles which corresponds to the lung deposi- concentration with respect to reaction time under tion of particles to a certain individual. This different ozone concentration which were mea- demonstrates the personal exposure to ultra-fine sured by UCPC connected with SMPS. The mass particles based on the measurement of particle concentration reached its peak value higher and surface area. Based on this measurements, pass- earlier at high ozone concentration (100 ppb) at engers can have a maximum deposition of nano- 30°C and the particle number concentration shows particles in their lungs around 40 min. the same trend under the same experimental con- Figure 6 shows the size distribution and growth ditions. The peak mass concentration under 50 of particles in the chamber at 30°C after 10 ppb ozone and 30°C was 19.1 μg/m3 at 90 min, while that under 100 ppb and 30°C was 24.1 μ g/m3 at 35 min. This suggests that more semi- volatile products are formed at high initial ozone concentration and have significant influence on the growth of the particles. Ozone was continu- ously introduced into the chamber but the parti- cle number concentration continuously decreased. This indicates that the emitted monoterpenes from the air freshener was consumed by ozone after approximately 50 min. Particles less than 10 nm were detected in all Figure 5. Measurement of particle surface concen- experimental conditions. The particles having ~ tration and its correlation with the depo- sited surface area in human lung.

Figure 4. The variations of particle number con- centration and mass concentrations at Figure 6. The variation of particle size distri- 30°C with low ozone (50 ppb) and with bution at 30°C with low ozone (50 high ozone (100 ppb) measured by ppb), and with high ozone (100 ppb) UCPC connected with SMPS. after 10 min, 30 min, and 90 min.

ENVIRONMENTAL ENGINEERING RESEARCH / VOL. 12, NO. 2, 2007 Ultra-Fine Particles and Gaseous Volatile Organic Compound Exposures from the Reaction of Ozone and Car-Air Freshener During Metropolis Travel 77 min, 30 min and 90 min. The particle diameters increased as reactions proceeded but the particle number concentrations consequently decreased. This implies that the particle growth mechanisms were carried out via condensation and then subsequent gas-to-particle partitioning of the reaction products. At high ozone concentration (100 ppb), the growth of particles was accelerated and the number of large particles increased as the reactions proceeded. Particle growth was observed to proceed even until 90 Figure 8. The variations of particle number con- min. centration and mass concentrations at Figure 7 shows particle properties to support 40°C with high ozone (100 ppb). the growth of particles in the chamber. The ini- tial mean particle diameter was in the range of rature decreases a chemical reaction rate. Figures 10 to 30 nm and increased to 120 nm at 30oC. 8 - 10 show the effect of temperature on the par- Particle diameter grew faster at high ozone con- ticle growth and its property. Figure 8 shows centration as shown in Figure 7. The high parti- that the mass concentration reached its peak value cle surface concentration at 30°C and high ozone earlier (30 min) under 100 ppb ozone and 40°C, concentration (100 ppb) in Figure 7 explains the which is 4 - 6 times lower than those under the observed rapid particle growth in 10 min at experimental conditions above. The particle num- Figure 6. This result further supports the fact ber concentration seems to increase continuously. that semi-volatile products form rapidly at initial The temperature change from 30 to 40°C pro- high ozone concentration, continue to condense, duced a lower particle mass concentration. The and grow through adsorbing onto existing particles. mass concentration maximum at 40°C and 100 ppb is 3.80 μg/m3 at 30 min (Figure 8). This is due mainly to the volatilization of semi-volatile species and subsequent formation of gas-phase products by the increase of temperature.18) The particle number concentrations at each particle size under high temperature (40°C) were low compared to those under low temperature (30°C) (Figure 6). The increase of particle number concentration at 40°C was slow and there was a long delay for 120 min (Figure 8). The delay period may Figure 7. The variations of surface concentration be caused by volatilization of semi-volatile pro- and mean particle diameter at 30°C ducts by high temperature. Therefore, it took with low ozone (50 ppb) and with high ozone (100 ppb). time for the semi-volatile products to reach to their satisfactory concentrations for the particle Temperature Effects on Particle Formation nucleation. Although some particle formation has According to an indoor chemistry and exposure been observed, it does not seem to significantly model, indoor secondary organic concen- affect the growth to larger particles (Figures 9 trations are expected to increase by a factor of and 10). These results imply that daytime temp- two for every 10°C decrease in indoor tempera- eratures (or high summer temperatures) tend to tures.14) This is anticipated because lower tempe decrease particle concentrations, while cooler night-

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during the ozone-initiated reactions with emitted monoterpenes (Table 1). The increase of tempe- rature could allow the chemical species to leave the particle phase and re-establish the gas-particle equilibrium. Formaldehyde was detected in all experimental conditions, while acetone was detec- ted only at 40°C at 100 ppb ozone. Formaldehyde was easily detected in all experimental condi- tions since it formed as a primary carbonyl com- pound during the ozonation of biogenic VOCs.4) The concentration of acrolein was high compared Figure 9. The variation of particle size distri- to other compounds. Higher concentrations of bution at 40°C with high ozone (100 acetaldehyde were detected at the higher temper- ppb) after 10 min, 30 min, and 90 min. ature which supports the fact that semi-volatile compounds remain in the gaseous phase. How- ever, a curious deviation from the trend was observed with propionaldehyde which showed a lower concentration at 40°C. Other chemicals (such as formaldehyde at 30°C and 120 min and acetone at 40°C and 120 min) also deviated substantially. Sampling artifacts might contribute to these results. Further investigations may be undertaken to confirm the irregularity with propio- naldehyde, formaldehyde at 30°C and 120 min and acetone at 120 min and 40°C. The observed increase of concentrations of formaldehyde in Figure 10. The variations of surface concentration other cases, acetaldehyde and acrolein shows and mean particle diameter at 40°C that they are secondary products of the oxidation with high ozone (100 ppb). process and accumulates in the chamber. time temperatures lead to significantly increased CONCLUSIONS yields. We demonstrated the formation and growth of Gaseous Products particles as well as the gaseous products during Low molecular carbonyls, i.e., acetone, formal- the ozone-initiated reactions with biogenic VOCs dehyde, and acetaldehyde were also observed emitted from a car air freshener. The effects of

Table 1. Gaseous products ( and ketone) during the ozone-initiated oxidation. Concentrations are in ppm Time (min) Condition Form Ace Acro Acn Prop 60 0.003 0.015 0.153 ND ND 120 30°C - 100 ppb 0.084 ND 0.211 ND ND 300 0.005 ND 0.264 ND 0.056 60 0.004 0.675 ND ND ND 120 40°C - 100 ppb 0.024 0.742 ND 0.183 ND 300 0.055 ND 0.336 ND 0.008 Form - formaldehyde Acn - acetone Ace - acetaldehyde Prop - propionaldehyde Acro - acrolein ND - not detected

ENVIRONMENTAL ENGINEERING RESEARCH / VOL. 12, NO. 2, 2007 Ultra-Fine Particles and Gaseous Volatile Organic Compound Exposures from the Reaction of Ozone and Car-Air Freshener During Metropolis Travel 79 temperature and ozone concentration on the forma- concentrations of glycol ethers and terpe- tion of the reaction products were investigated in noids, Indoor Air, 16, 179-191 (2006). this study. 4. Calogirou, A., and Larsen, B. R., Gas-phase Over the course of a typical metropolis travel, terpene oxidation products: a review, Atmos. ozone concentrations may vary depending on the Environ., 33, 1423-1439 (1999). dynamic ambient conditions. Based on the experi- 5. Weschler, C. J., and Shields, H. C., Potential mental results obtained here, the formation of reactions among indoor pollutants, Atmos. particles and gaseous products can be expected Environ., 31, 3487-3495 (1997). to occur during the ozone-initiated oxidations 6. Weschler, C. J., and Shields, H. C., Indoor with monoterpenes from the car air freshener ozone/terpene reactions as a source of indoor inside the vehicle. This can significantly affects particles, Atmos. Environ., 33, 2301-2312 the health of passengers in the vehicle. Relative (1999). humidity and air exchange rate were not consi- 7. Li, T. H., Turpin, B. J., Shields, H. C., and dered in the study. Therefore, the results might Weschler, C. J., Indoor hydrogen peroxide be overestimated. The results are not intended as derived from ozone/d-limonene reactions, direct representations of specific ambient condi- Environ. Sci. Tech., 36, 3295-3302 (2002). tions. Nevertheless, it will serve as useful back- 8. Rohr, A. C., Weschler, C. J., Koutrakis, P., ground information to assess the importance of and Spengler, J. D., Generation and quantifi- temperature and ozone concentration fluctuations. cation of ultrafine particles through terpene/ The results can be used to better understand the dzone reaction in a chamber setting, Aeros. potential exposures of irritating or toxic reaction Sci. Tech., 37, 65-78 (2003). products to passengers that could be easily found 9. Oberdorster, G., Pulmonary effects of inhaled in confined spaces with high ozone content and ultrafine particles, Int. Arch. Occup. Environ. high temperature during hot summer seasons. Health, 74, 1-8 (2001). 10. Oberdorster, G., Oberdorster, E., and Ober- ACKNOWLEDGEMENT dorster, J., Nanotoxicology: an emerging dis- cipline evolving from studies ultrafine parti- This research was partially funded by Ministry cles, Environ. Health Perspect., 1113, 823-839 of Science and Technology project (Basic Science (2005). Research Program). We also thankfully acknow- 11. Moller, W., Brown, D. M., Kreyling, W. G., ledged the Korea Institute of Science and Tech- and Stone, V., Ultrafine particles cause cys- nology for the partial financial support of the toskeletal dysfunctions in macrophages: role research. of intracellular calcium, Particle and Fibre Toxic., 2, 7 (2005). REFERENCES 12. Sarwar, G., Corse, R., Allen, D., and Wes- chler, C. J., The significance of secondary 1. Weschler, C. J., Ozone in indoor environ- organic aerosol formation and growth in ments: Concentration and chemistry, Indoor buildings: experimental and computational Air, 10, 269-288 (2000). evidence, Atmos. Environ., 37, 1365-1381 (2003). 2. Nazaroff, W. W., and Weschler, C. J., Clea- 13. Takekawa, H., Minoura, H., and Yamazaki, ning products and air fresheners: Exposure S., Temperature dependence of secondary to primary and secondary air pollutants, Atmos. organic aerosol formation by photo-oxidation Environ., 38, 2841-2865 (2004). of hydrocarbons, Atmos. Environ., 37, 3413- 3. Singer, B. C., Destaillats, H., Hodgson, A. 3424 (2003). T., and Nazaroff, W. W., Cleaning products 14. Sheenan, P. E., and Bowman, F. M., Estimated and air fresheners:emissions and resulting effects of temperature on secondary organic

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