Scholarly article on topic 'Hygroscopic effects on the mobility and mass of cigarette smoke particles'

Hygroscopic effects on the mobility and mass of cigarette smoke particles Academic research paper on "Earth and related environmental sciences"

CC BY
0
0
Share paper
Academic journal
Journal of Aerosol Science
Keywords
{"Cigarette smoke" / Tobacco / Hygroscopic / Mobility / Mass}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — Tyler J. Johnson, Jason S. Olfert, Caner U. Yurteri, Ross Cabot, John McAughey

Abstract The hygroscopic growth of particles, produced from a University of Kentucky 3R4F reference cigarette smoked following Health Canada Intense (HCI) puffing parameters (55mL puff of 2s duration, every 30s), was measured in terms of the electrical mobility diameter and particle mass, using a Hygroscopic Tandem Differential Mobility Analyzer (HTDMA) and Centrifugal Particle Mass Analyzer (CPMA) system. Both the particle mobility diameter and mass growth factors were found to agree with previously determined values and hygroscopicity models. The mobility diameter growth factor of the particles produced from either a University of Kentucky 3R4F or 1R5F reference cigarette, following HCI puffing parameters, were found to be very similar. As the relative humidity (RH) approached saturation, the effects of the initial particle size on the mobility growth factor became more dominant, with larger particles growing proportionally larger than smaller particles. From the measured mobility diameter and mass growth factors, the density growth factor was calculated. This parameter showed that the particle density increased as the sample relative humidity increased. This case is only possible, given that the dried smoke particle density (1109±118kg/m3) was determined to be greater than the density of water, if the water condensation on the smoke particle dissolves at least a portion of it, resulting in a significant increase in mass with only a small increase volume.

Academic research paper on topic "Hygroscopic effects on the mobility and mass of cigarette smoke particles"

Author's Accepted Manuscript

Hygroscopic effects on the mobility and mass of cigarette smoke particles

Tyler J. Johnson, Jason S. Olfert, Caner U. Yurteri, Ross Cabot, John McAughey

www.elsevier.com/locate/jaerosci

PII: S0021-8502(15)00058-0

DOI: http://dx.doi.org/10.1016/jjaerosri2015.04.005

Reference: AS4878

To appear in: Journal of Aerosol Science

Received date: 21 January 2015 Revised date: 10 April 2015 Accepted date: 14 April 2015

Cite this article as: Tyler J. Johnson, Jason S. Olfert, Caner U. Yurteri, Ross Cabot, John McAughey, Hygroscopic effects on the mobility and mass of cigarette smoke particles, Journal of Aerosol Science, http://dx.doi.org/10.1016/j. jaerosci.2015.04.005

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Hygroscopic effects on the mobility and mass of cigarette smoke particles

Tyler J. Johnsona, Jason S. Olferta, Caner U. Yurterib, Ross Cabotb and John McAugheyb aDepartment of Mechanical Engineering, University of Alberta, Edmonton, Alberta, T6G 2G8, Canada bBritish American Tobacco, Group Research & Development, Southampton, SO15 8TL, U.K. Corresponding author: J.S. Olfert

Tel.: +1 780 492 2341; Fax: +1 780 492 2200; Email address: jolfert@ualberta.ca Shorten Running Title: Hygroscopicity of cigarette smoke particles

Abstract

The hygroscopic growth of particles, produced from a University of Kentucky 3R4F reference cigarette smoked following Health Canada Intense (HCI) puffing parameters (55 mL puff of 2 s duration, every 30 s), was measured in terms of the electrical mobility diameter and particle mass, using a Hygroscopic Tandem Differential Mobility Analyzer (HTDMA) and Centrifugal Particle Mass Analyzer (CPMA) system. Both the particle mobility diameter and mass growth factors were found to agree with previously determined values and hygroscopicity models. The mobility diameter growth factor of the particles produced from either a University of Kentucky 3R4F or 1R5F reference cigarette, following HCI puffing parameters, were found to be very similar. As the relative humidity (RH) approached saturation, the effects of the initial particle size on the mobility growth factor became more dominant, with larger particles growing proportionally larger than smaller particles. From the measured mobility diameter and mass growth factors, the density growth factor was calculated. This parameter showed that the particle density increased as the sample relative humidity increased. This case is only possible, given that the dried smoke particle density (1109 ± 118 kg/m3) was determined to be greater than the density of water, if the water condensation on the smoke particle dissolves at least a portion of it, resulting in a significant increase in mass with only a small increase volume.

1. Introduction

Tobacco smoking is a recognised dose-related health risk (Doll et al., 2004; International Agency for Research on Cancer, 2004; U.S. Department of Health and Human Services, 2010) resulting from the chronic exposure to tobacco smoke toxicants (Fowles & Dybing, 2003; U.S. Department of Health and Human Services, 2012). These substances affect the body via mechanisms of inflammation or oxidative stress, or more specific toxic mechanisms depending on the exposure (Stratton et al., 2001).

Smoke dosimetry is an important part of any toxicological assessment, and deposition and retention mechanisms will vary with the physical and chemical form of each compound, but also with the bulk aerosol properties of the particle phase (International Commission for Radiological Protection, 1994; Baker & Dixon, 2006; St. Charles et al., 2013). Tobacco smoke is a dynamic mixture of particulate and vapour phases consisting of more than six thousand individual substances (Rodgman & Perfetti, 2013). It contains both hydrophilic and hydrophobic species and therefore the potential hygroscopic growth of the smoke droplets may be a significant parameter in modelling particle behaviour on inhalation.

Many characteristics of cigarette smoke have been studied, such as its composition (Counts et al., 2005; Adam & Baker, 2007; Rodgman & Perfetti, 2013), mobility size distribution (Adam et al., 2009) and effective density (Lipowicz, 1988; Chen et al., 1990; Johnson et al., 2014). However, only a few studies have measured the hygroscopic mobility diameter growth of cigarette smoke particles. Ishizu et al. (1980) measured the hygroscopic diameter growth factor of poly-dispersed particles, produced from a 70 mm long, blended plain cigarette smoked with a 35 mL puff volume over 2 s, using a light scattering photometer. The study mixed the streams produced by a water bubbler and compressed air to control the humidity and measured growth factors of 1.00 to 1.05 over a 55% to 74% relative humidity (RH) range. Kousaka et al. (1982) however found no significant hygroscopic mobility diameter growth of poly-dispersed cigarette smoke particles, with diameters in the 2 to 8 ^m range, exposed to any relative humidity less than or equal to 100% RH, using an ultramicroscopic sedimentation size analyzer. The particles were produced from Wakaba brand cigarettes, diluted one hundred times to avoid coagulation and exposed to the humidity condition for 10 to 30 seconds. The relative humidity was controlled by varying the mixing ratio of humid and dried airstreams generated by a bubbler and silica bed respectively. Li & Hopke (1993), using a Tandem Differential Mobility Analyzer (TDMA) with a wetted wall reactor and bubbler, determined a mobility growth factor of 1.38 to 1.61 for diluted mono-dispersed mainstream smoke particles (with mobility diameters from 150 to 400 nm respectively) exposed to 99% RH or greater. A chilled mirror dew point hygrometer was used to measure the relative humidity within the system. Hicks et al. (1989) determined a growth factor of 1.7 for mainstream cigarette smoke using a quartz crystal microbalance cascade impactor to compare the size distribution after it was inhaled, humidified to supersaturation in the lung and exhaled by test subjects (MMAD = 0.47 ^m; GSD = 1.4) versus when the exhaled aerosol sample was dried (MMAD = 0.28 ^m; GSD = 1.72). However, all of these studies either considered a poly-dispersed aerosol or a limited relative humidity range (>99% RH).

To the authors' knowledge, only one study has measured the hygroscopic mass growth of cigarette smoke particles. Ishizu et al. (1980) used a microbalance with a silver membrane filter to measure the weight change of cigarette smoke particles (diluted a 1000 fold) when exposed to changing relative humidity. However, this study only considered poly-dispersed cigarette smoke particles.

This study determines the hygroscopic growth of cigarette smoke particles, in terms of both particle mobility diameter and mass, using the combination of Hygroscopic Tandem Differential Mobility Analyzer (HTDMA) and Centrifugal Particle Mass Analyzer (CPMA) system. These measurements will be compared against previous work in the field and used to draw conclusions regarding particle composition. The effect of initial particle size and cigarette type on hygroscopic cigarette particle mobility diameter growth will also be investigated. Hygroscopicity data is crucial to accurately model lung deposition, an active area of research (Hofmann et al., 2001; Robinson & Yu, 2001; Schroeter et al., 2001; Broday & Robinson, 2003; Longest & Xi, 2008; Kane et al., 2010; Longest & Hindle, 2010; Zhang et al., 2012; Kleinstreuer & Feng, 2013; Pichelstorfer et al., 2013; Xi et al., 2013).

2. Experimental apparatus

Cigarette smoke was generated by smoking University of Kentucky (2014) 3R4F or 1R5F reference cigarettes using a Borgwaldt KC RM20D smoking machine (Hamburg, Germany) following Health Canada Intense (HCI) puffing parameters; 55 mL puff of 2 s duration every 30 s, but without vent blocking (Canada, 2014). The smoke produced from 1 cigarette undergoing 12 puffs was collected in 25 L Tedlar® bags

prefilled with 24 L of HEPA filtered dilution air. These two reference cigarettes were chosen due to their contrasting tar and nicotine yields, as reported in Table 1.

The Tandem Differential Mobility Analyzer (TDMA; Stolzenburg, 1988) apparatus used to measure the mobility diameter growth factor of the cigarette smoke is shown in Figure 1. Similar to Biskos et al. (2006a), the humidity of each flow was controlled by varying the mixing ratios of dried and humidified air streams using mass flow controllers (FC). The humidified air streams were generated using Perma Pure MH-110-48S-4 Nafion humidifiers (Toms River, United States) filled with deionized water, while the dry air streams were generated by expanding HEPA filter compressed air. The Nafion humidifiers were temperature controlled in heated water baths to avoid freezing the deionized water as humidification is an endothermic process. The sample flow was drawn using the TSI 3375 Condensation Particle Counter (CPC; Minnesota, United States) internal vacuum pumps, while the TSI 3080 Differential Mobility Analyzer (DMA; Minnesota, United States) sheath flows were supplied to the column with compressed air and removed with a critical orifice (CO) regulating the flow drawn by a vacuum pump.

To establish the base state, the aerosol was first dried using a MD-110-48S-4 Nafion dryer (Dryer 1). The relative humidity of the aerosol at the dryer exit was controlled by varying the purge gas flow rate through the dryer using FC1 and measured with a Sensirion SHT75 RH Sensor (Zurich, Switzerland) placed directly in the aerosol flow (RH1). A Kr-85 radioactive neutralizer was used to apply a bipolar charge distribution to the dried aerosol before it was classified by DMA 1. The relative humidity of DMA 1's sheath flow was also measured using a SHT75 RH Sensor (RH2) and matched to RH1 (to maintain the sample's environment in the DMA) by varying the mixing ratio of the humidified and dried air streams using FC2 and FC3 respectively. A cooling coil (CC1) was used to ensure the two streams were thoroughly mixed and reached the sample temperature before the RH was measured. DMA 1 was then used to select particles with one electrical mobility diameter or the correct electrostatic to drag force ratio from the poly-dispersed aerosol (Knutson & Whitby, 1975). The mono-dispersed particles were then reconditioned to another relative humidity using Humidifier 2 (MH-110-48S-4) and/or Dryer 2 (MH-110-48S-4) depending on the orientation of the three-way valves (TW1 and TW2). Dryer 2 was able to dry or humidify the sample depending on the relative humidity of the purge gas, which was controlled by the mixing ratio of the humidified and dried air streams (by FC4 and FC5 respectively). After ensuring thorough mixing and a stable temperature with CC2, the sample's relative humidity was measured with another SHT75 RH Sensor (RH3) placed directly in the aerosol flow. The sample flow was then split equally between CPC 1 and DMA 2. CPC 1 measured the particle number concentration (N1) of the aerosol by condensing butanol onto the particles until they were large enough to be detected optically (Agarwal & Sem, 1980). DMA 2's sheath flow relative humidity was matched to RH3 (by controlling the mixing ratio of humidified and dried air streams with FC6 and FC7) and was measured with a Rotronic MBW973-CA optical dew-point hygrometer (West Sussex, UK). The hygrometer was used to measure RH4, in preference to a SHT75 RH Sensor, for its higher accuracy as this sheath flow dominates the conditioning of the aerosol while it is being measured in the TDMA. Unlike DMA 1 which was at a constant mobility setpoint, DMA 2 was used to scan across the mobility size range of the reconditioned particles. This was accomplished by measuring the particle number concentration of the classified particles (N2) with CPC 2 and recording these values as a function of DMA's 2 stepping mobility setpoint.

The effects of reconditioning the aerosol between DMA 1 and DMA 2 on the particle mobility diameter were quantified by applying the TDMA inversion theory developed by Stolzenburg and McMurry (2008). The

inversion assumed that each particle growth/shrinkage mode had a log-normal distribution and involved calculating the theoretical DMA transfer functions of both DMAs from the measured operating parameters and fitting the resulting theoretical model to the measured data. This fit was applied by minimizing the weight, factor and distribution of each particle growth mode using chi-squared constrained minimization in Matlab.

Similar to Vlasenko and Mikhailov (2013), the particle mass growth factor due to hygroscopic effect was determined using a Cambustion CPMA (Cambridge, UK) as shown in Figure 2. A CPMA selects particles of a set mass-to-charge ratio by balancing opposing electrostatic and centrifugal forces (Olfert & Collings, 2005). The CPMA apparatus was very similar to the TDMA apparatus described previously. The sample was still conditioned, mobility selected by DMA 1 and reconditioned. However, the reconditioning effects on the particles were measured by scanning the mass of the reconditioned particles with the CPMA, rather than the mobility with DMA 2. By recording the number concentration measured by CPC 2 as a function of the different mass setpoints and applying a log-normal fit through chi-squared minimization to this data (Johnson et al., 2013), the effects of reconditioning on the particle mass were determined.

The sample in the CPMA is heated slightly due to the friction generated by the cylinders rotating and the heat produced from the electric motor. This heating becomes detrimental when measuring at any high relative humidity (>85% RH) as a small increase in sample temperature significantly drops the sample relative humidity and thus changes the hygroscopic particle mass growth being measured. This effect was quantified by placing an additional SHT75 RH Sensor on the outlet of the CPMA (RH5), thus measuring the change in the sample relative humidity across the CPMA (RH3 vs. RH5). This change in RH was limited to a few percent by running the CPMA intermittently (allowing it to cool), operating the CPMA at a lower resolution (resulting in a lower cylinder speed, thus generating less heat) and increasing the sample flow rate through the CPMA to 1.5 LPM (decreasing the particle residence time and thus the exposure time to the temperature gradient in the CPMA). Unless otherwise stated, the reported CPMA RH for each test is the average RH recorded by RH3 and RH5.

Measurements were only taken when the system was stable. The system was considered stable when twice the standard deviation of the relative humidity measurements at each location over the system scan time (a 95% confidence interval assuming a normal distribution) was within the manufacturer stated uncertainty of that sensor. For the TDMA system this was a combination of three SHT75s with a 1.8% RH uncertainty and a MBW-973 hygrometer with a 0.5% RH uncertainty. The DMA-CPMA system used four SHT75s, each with a 1.8% RH uncertainty. All of the SHT75s were calibrated at the beginning and end of the campaign with the hygrometer to verify their accuracy and drift over the time period data were collected.

3. Theory

TDMA setups have been used extensively to determine the hygroscopic mobility diameter growth of nonvolatile aerosol particles, such as NaCl (Li et al., 1992; Biskos et al., 2006a, 2006b; Park et al., 2009), (NH4)2SO4 (Li et al., 1992; Park et al., 2009), (NH4)HSO4 (Li et al., 1992) and combustion aerosols (Li & Hopke, 1993). However, cigarette smoke is semi-volatile (Tang et al., 2012) and as a result particle evaporation, approximately 5% in mobility diameter (independent of size in the range tested), was observed as the particles were maintained at a dry state between DMA 1 and DMA 2. This evaporation

could be attributed to the other volatile components evaporating, such as nicotine (Counts et al., 2005) and semi-volatile organics (Tang et al., 2012), as the DMA sheath flows and Nafion conditioners only balanced the water content of the aerosol sample. Since the objective of this work is to determine the growth factor due to humidification, the mobility-diameter growth factor (GFd) is defined as

GFd (1)

d2 DRY

where o2,wet is the geometric mean particle mobility diameter when conditioned in a humidified environment and d2DRY is the geometric mean particle mobility diameter when conditioned in a dry environment, so particle evaporation does not bias the measurement. Similarly, the mass growth factor (GFm) is defined as

GFm = mvEL (2)

where mWET is the geometric mean particle mass when conditioned in a humidified environment and mDRY is the geometric mean particle mass when conditioned in a dry environment.

4. Results and discussion

The mobility diameter growth factors (GFd), determined for 236.3 ± 8.8 nm particles produced from a University of Kentucky 3R4F reference cigarette following HCI puffing parameters, are shown in Figure 3. The horizontal errors bars represent the bias uncertainty of the MBW973 hygrometer determined by the manufacturer.

Figure 3 shows no appreciable mobility diameter growth (>5%) was measured until the relative humidity was 85% or higher. The maximum mobility diameter growth factor measured was 1.27 at 96% RH. These results do not agree with Kousaka et al. (1982), who only measured considerable mobility diameter growth for supersaturated conditions. On the other hand, Figure 4 shows these results agree within error and/or follow the same trends as other hygroscopic cigarette smoke data collected (Ishizu et al., 1980; Li & Hopke, 1993) and previously generated hygroscopicity models of cigarette smoke (Ishizu et al., 1980; Robinson & Yu, 1998; Longest & Xi, 2008).

Figure 5 appears to show that the initial particle size had no discernible effect on the hygroscopic mobility diameter growth factor. However the average mobility growth factor and precision uncertainty at 97% RH was 1.15±0.05, 1.18±0.04 and 1.20±0.01 for a 95.2, 236 and 371 nm particle respectively. Furthermore, the difference between the average mobility growth factor with an initial particle size of 371 nm versus 95.2 nm was found to be 0.0017, 0.0212 and 0.0482 at 48%, 91% and 97% RH respectively. Therefore, the effect of larger particles growing proportionally larger than smaller particles was found to increase as the relative humidity approached saturation. This theory is supported by the modelled cigarette smoke results by Robinson and Yu (1998). At 99.5% RH, Robinson and Yu (1998) determined a growth factor of 1.37 for a 170 nm smoke particle and 1.50 for a 440 nm smoke particle or a 13% difference in growth due to the initial particle size. At 100% RH, they determined a growth factor of 1.75 for a 170 nm smoke particle and

2.62 for a 440 nm smoke particle or an 87% difference in growth due to the initial particle size. Therefore, a 0.5% relative humidity increase near saturation caused the initial particle size to shift the growth factor an additional 0.74.

Figure 6 shows that the mobility diameter growth factor measured from the particles produced from 3R4F and 1R5F University of Kentucky reference cigarettes follow similar trends. This agrees with Tang et al. (2012), who determined that the 3R4F and 1R5F cigarettes smoked following ISO puffing parameters (35 cm3 per puff over a 2 second duration with once a minute frequency) using a Walton Smoking Machine produced particles with similar hygroscopicity.

As described in Equation (2), the hygroscopic mass growth factor was determined by dividing the particle mass measured at higher RHs by the particle mass measured at the dry state (<25% RH). The average dry particle mass, with DMA 1 selecting a mobility diameter of 257.3 ± 7.7 nm, was 7.7 ± 0.4 fg. Assuming the same particle evaporation occurred between the outlet of DMA 1 and the CPMA inlet as between the outlet of DMA 1 and DMA 2 inlet (i.e. the CPMA classified a 236.3 ± 8.8 nm particle), a dry effective particle density of 1109 ± 118 kg/m3 was determined. This value agrees within error with the previously determined values, such as an effective density of 1180±113 kg/m3 (Johnson et al., 2013) and mass-weighted average effective density of 1120±40 kg/m3 (Lipowicz, 1988).

The mass growth factors (GFm), determined for particles produced from a University of Kentucky 3R4F reference cigarette following HCI puffing parameters are shown in Figure 7. The horizontal error bars represent the possible RH range that the sample was exposed to within the CPMA. These limits were determined by calculating the uncertainty in the relative humidity measured at its inlet (RH3) and outlet (RH5) using root-mean-squared to combine each source of uncertainty, including the precision uncertainty of RH3 and RH5 (determined from their calibration against the hygrometer), the drift of each sensor measured over the duration of the campaign, the difference between the two sensors during each measurement and the accuracy of the hygrometer as stated by the manufacturer.

Figure 7 shows appreciable mass growth (>5%) started at a lower relative humidity (74% RH) compared with when the mobility diameter growth became significant (85% RH). This difference could be due the sensitivity of the systems, as a 1% growth in the particle mobility diameter results in a 3% increase in particle mass if the volume is conserved. Another possibility is the initial water that condenses onto the particle, dissolves a portion of the particle, resulting in a significant increase in mass, but only a small increase in volume. It is likely that this difference in appreciable mass versus mobility diameter growth is a combination of the two effects as discussed further below.

The maximum mass growth factor measured was 1.53 at 93.7% RH. These results agree within error with the mass growth factors measured by Ishizu et al. (1980) using silver membrane filters and a microbalance. While a majority of the data do not agree within error with the mass hygroscopicity model developed by Ishizu et al. (1980), the data follow a similar trend.

Since cigarette smoke particles have a spherical morphology (Johnson et al., 2014), the particle volume (V) can be determined from,

V=n d3

and the particle mass (m) from,

m=6 pdm (4)

where p is the effective density of the particle and dm is the particle mobility diameter. Similar to the definitions of mobility diameter and mass growth factors (Equations (1) and (2)), the volume growth factor (GFV) can be defined as

GFy = VWl (5)

Substituting Equation (1) and Equation (3) into Equation (5) gives,

~ 2,DRY 6

Furthermore, by combining Equation (4), then Equation (6) into Equation (2), the result can become

nn d 3

« P2,WETd2,WET p _ 6 _p2,WET

6 P2,DRYd

GFd3 =

Finally, by rearranging Equation (7) the result becomes

P?lWEL=Gt=GFp (8)

P2,DRY GFV

which is equivalent to the particle density growth factor. This parameter was calculated from the measured mass and volume growth factors and is shown in Figure 8. Since the mass and volume growth factors were determined independently, the values were measured over the same range, but at slightly different RH values. Therefore to calculate the particle density growth factor, the mass and volume values were fitted with simple exponential growth equations through constrained chi-squared minimization as shown in Figure 8.

The particle density growth factor can be used as an indicator of the particle composition and solubility characteristics. If the particle density growth factor is greater than one or the density is increasing, the particle mass is increasing at a faster rate than the particle volume. Since mass is conserved, this

difference in mass versus volume growth for spherical particles (with no voids) can be due to two different mechanisms:

1.) One or multiple components of the particle dissolving in the water, resulting in a significant increase in particle mass, but only a small increase in particle volume.

2.) A significant difference between the density of the particle components and water, resulting in the overall density tending towards the density of the more prevalent constituent.

It is unlikely mechanism 2 dominated the density growth factor as the density of the dry particles (~1109 kg/m3 previously determined) is greater than the density of the water (1000 kg/m3). If this effect was occurring, the density growth factor would have decreased as the relative humidity increased. Therefore since the density growth factor depicted in Figure 8 is greater than one (accounting for the range of possible sample RHs within the CPMA), it is likely that at least portions of the dry particle dissolved in the water. This is consistent with the knowledge that the smoke droplet contains many hydrophilic components (Rodgman & Perfetti, 2013).

5. Conclusions and summary

A HTDMA and CPMA system was used to measure the mobility diameter and particle mass growth of cigarette smoke particles due to hygroscopic effects. The particles were produced from a University of Kentucky 3R4F reference cigarette smoked following HCI puffing parameters. These results agreed with the values and hygroscopicity models determined in previous studies. The mobility diameter growth factor of the particles produced from a 1R5F reference cigarette following HCI puffing parameters, were similar to the values measured from the 3R4F reference cigarette. At a common relative humidity, the mobility growth factor was found to increase as the initial particle size increased. This effect became more apparent as the relative humidity approached saturation. The calculated density growth factor showed that the particle density increased as the relative humidity increased. Given that the dried smoke particle density (1109 ± 118 kg/m3) was greater than the density of the water, this could only occur if the water condensing on the smoke particle dissolves at least a portion of it, resulting in a significant increase in mass with only a small increase volume.

Acknowledgements

This research was funded by British American Tobacco (Investments) Ltd. Bibliography

Adam, T., & Baker, R. R. (2007). Characterization of Puff-by-Puff Resolved Cigarette Mainstream Smoke by Single

Photon lonization-Time-of-Flight Mass Spectrometry and Principal Component Analysis. Journal of Agricultural and Food Chemistry, 55(6), 2055-2061. doi:10.1021/jf062360x

Adam, T., McAughey, J., McGrath, C., Mocker, C., & Zimmermann, R. (2009). Simultaneous on-line size and chemical analysis of gas phase and particulate phase of cigarette mainstream smoke. Analytical and Bioanalytical Chemistry, 394(4), 1193-1203. Retrieved from http://dx.doi.org/10.1007/s00216-009-2784-y

Agarwal, J. K., & Sem, G. J. (1980). Continuous flow, single-particle-counting condensation nucleus counter. Journal of Aerosol Science, 11(4), 343-357. doi:http://dx.doi.org/10.1016/0021-8502(80)90042-7

Baker, R. R., & Dixon, M. (2006). The Retention of Tobacco Smoke Constituents in the Human Respiratory Tract. Inhalation Toxicology, 18(4), 255-294. doi:10.1080/08958370500444163

Biskos, G., Malinowski, A., Russell, L. M., Buseck, P. R., & Martin, S. T. (2006a). Nanosize Effect on the Deliquescence and the Efflorescence of Sodium Chloride Particles. Aerosol Science and Technology, 40(2), 97-106. doi:10.1080/02786820500484396

Biskos, G., Russell, L. M., Buseck, P. R., & Martin, S. T. (2006b). Nanosize effect on the hygroscopic growth factor of aerosol particles. Geophysical Research Letters, 33(7). doi:10.1029/2005GL025199

Broday, D. M., & Robinson, R. (2003). Application of Cloud Dynamics to Dosimetry of Cigarette Smoke Particles in the Lungs. Aerosol Science and Technology, 37(6), 510-527. doi:10.1080/02786820300969

Canada. (2014). Canada Government Tobacco Act: Tobacco Reporting Regulations, SOR/2000-273, Part3: Emissions from designated tobacco products. Health Canada.

Chen, B. T., Namenyi, J., Yeh, H. C., Mauderly, J. L., & Cuddihy, R. G. (1990). Physical Characterization of Cigarette Smoke Aerosol Generated from a Walton Smoke Machine. Aerosol Science and Technology, 12(2), 364-375. doi:10.1080/02786829008959352

Counts, M. E., Morton, M. J., Laffoon, S. W., Cox, R. H., & Lipowicz, P. J. (2005). Smoke composition and predicting relationships for international commercial cigarettes smoked with three machine-smoking conditions. Regulatory Toxicology and Pharmacology, 41(3), 185-227. doi:http://dx.doi.org/10.1016/j.yrtph.2004.12.002

Doll, R., Peto, R., Boreham, J., & Sutherland, I. (2004). Mortality in relation to smoking: 50 years observations on male British doctors. BMJ, 328(7455), 1519. doi:10.1136/bmj.38142.554479.AE

Fowles, J., & Dybing, E. (2003). Application of toxicological risk assessment principles to the chemical constituents of cigarette smoke. Tobacco Control, 12(4), 424-430. doi:10.1136/tc.12.4.424

Hicks, J. F., Pritchard, J. N., Black, A., & Megaw, W. J. (1989). Measurements of growth due to condensation for some common aerosols. Journal of Aerosol Science, 20(3), 289-292. doi:http://dx.doi.org/10.1016/0021-8502(89)90004-9

Hofmann, W., Morawska, L., & Bergmann, R. (2001). Environmental tobacco smoke deposition in the human

respiratory tract: Differences between experimental and theoretical approaches. Journal of Aerosol Medicine, 14(3), 317-326. doi:10.1089/089426801316970277

International Agency for Research on Cancer. (2004). Volume 83: Tobacco Smoke and Involuntary Smoking. Lyon.

International Commission for Radiological Protection. (1994). ICRP Publication 66. Human Respiratory Tract Model for Radiological Protection. Annals of the ICRP, 24(1-3).

Ishizu, Y., Ohta, K., & Okada, T. (1980). The Effect of Moisture on the Growth of Cigarette Smokes Particles. Beitrage Zur Tabakforschung International, 10(3), 161-168.

lS03308:2012. (2012). Routine analytical cigarette-smoking machine -- Definitions and standard. Geneva: International Standard Organization.

Johnson, T. J., Olfert, J. S., Cabot, R., Treacy, C., Yurteri, C. U., Dickens, C.,... Symonds, J. P. R. (2014). Steady-state measurement of the effective particle density of cigarette smoke. Journal of Aerosol Science, 75(0), 9-16. doi:http://dx.doi.org/10.1016/j.jaerosci.2014.04.006

Johnson, T. J., Symonds, J. P. R., & Olfert, J. S. (2013). Mass-Mobility Measurements Using a Centrifugal Particle Mass Analyzer and Differential Mobility Spectrometer. Aerosol Science and Technology, 47(11), 1215-1225. doi:10.1080/02786826.2013.830692

Kane, D. B., Asgharian, B., Price, 0. T., Rostami, A., & Oldham, M. J. (2010). Effect of smoking parameters on the particle size distribution and predicted airway deposition of mainstream cigarette smoke. Inhalation Toxicology, 22(3), 199-209. Retrieved from

http://login.ezproxy.library.ualberta.ca/login?url=http://search.ebscohost.com/login.aspx?direct=true&db=afh &AN=48027034&site=ehost-live&scope=site

Kleinstreuer, C., & Feng, Y. (2013). Lung Deposition Analyses of Inhaled Toxic Aerosols in Conventional and Less

Harmful Cigarette Smoke: A Review. International Journal of Environmental Research and Public Health, 10(9), 4454-4485. doi:10.3390/ijerph10094454

Knutson, E. O., & Whitby, K. T. (1975). Aerosol classification by electric mobility: apparatus, theory, and applications. Journal of Aerosol Science, 6(6), 443-451. doi:http://dx.doi.org/10.1016/0021-8502(75)90060-9

Kousaka, Y., Okuyama, K., & Wang, C.-S. (1982). Response of Cigarette Smoke Particles to Change in Humidity. Journal of Chemical Engineering of Japan, 15(1), 75-76. doi:10.1252/jcej.15.75

Li, W., & Hopke, P. K. (1993). Initial Size Distributions and Hygroscopicity of Indoor Combustion Aerosol Particles. Aerosol Science and Technology, 19(3), 305-316. doi:10.1080/02786829308959638

Li, W., Montassier, N., & Hopke, P. K. (1992). A System to Measure the Hygroscopicity of Aerosol Particles. Aerosol Science and Technology, 17(1), 25-35. doi:10.1080/02786829208959557

Lipowicz, P. J. (1988). Determination of cigarette smoke particle density from mass and mobility measurements in a millikan cell. Journal of Aerosol Science, 19(5), 587-589. doi:http://dx.doi.org/10.1016/0021-8502(88)90210-8

Longest, P. W., & Hindle, M. (2010). CFD simulations of enhanced condensational growth (ECG) applied to respiratory drug delivery with comparisons to in vitro data. Journal of Aerosol Science, 41(8), 805-820. doi:http://dx.doi.org/10.1016/j.jaerosci.2010.04.006

Longest, P. W., & Xi, J. (2008). Condensational Growth May Contribute to the Enhanced Deposition of Cigarette Smoke Particles in the Upper Respiratory Tract. Aerosol Science and Technology, 42(8), 579-602. doi:10.1080/02786820802232964

Olfert, J. S., & Collings, N. (2005). New method for particle mass classification - the Couette centrifugal particle mass analyzer. Journal of Aerosol Science, 36(11), 1338-1352. doi:10.1016/j.jaerosci.2005.03.006

Park, K., Kim, J.-S., & Miller, A. L. (2009). A study on effects of size and structure on hygroscopicity of nanoparticles using a tandem differential mobility analyzer and TEM. Journal of Nanoparticle Research, 11(1), 175-183. Retrieved from http://dx.doi.org/10.1007/s11051-008-9462-4

Pichelstorfer, L., Winkler-Heil, R., & Hofmann, W. (2013). Lagrangian/Eulerian model of coagulation and deposition of inhaled particles in the human lung. Journal of Aerosol Science, 64(0), 125-142. doi:http://dx.doi.org/10.1016/j.jaerosci.2013.05.007

Robinson, R. J., & Yu, C. P. (1998). Theoretical Analysis of Hygroscopic Growth Rate of Mainstream and Sidestream Cigarette Smoke Particles in the Human Respiratory Tract. Aerosol Science and Technology, 28(1), 21-32. doi:10.1080/02786829808965509

Robinson, R. J., & Yu, C. P. (2001). Deposition of Cigarette Smoke Particles in the Human Respiratory Tract. Aerosol Science and Technology, 34(2), 202-215. doi:10.1080/027868201300034844

Rodgman, A., & Perfetti, T. A. (2013). The Chemical Components of Tobacco and Tobacco Smoke (Second.). Boca Raton: CRC Press.

Schroeter, J. D., Musante, C. J., Hwang, D., Burton, R., Guilmette, R., & Martonen, T. B. (2001). Hygroscopic Growth and Deposition of Inhaled Secondary Cigarette Smoke in Human Nasal Pathways. Aerosol Science and Technology, 34(1), 137-143. doi:10.1080/02786820117094

St. Charles, F. K., McAughey, J., & Shepperd, C. J. (2013). Methodologies for the quantitative estimation of toxicant dose to cigarette smokers using physical, chemical and bioanalytical data. Inhalation Toxicology, 25(7), 383397. doi:10.3109/08958378.2013.794177

Stolzenburg, M. (1988). An ultrafine aerosol size distribution measuring system. ProQuest Dissertations and Theses. University of Minnesota, Ann Arbor. Retrieved from

http://login.ezproxy.library.ualberta.ca/login?url=http://search.proquest.com/docview/303683946?accountid =14474

Stolzenburg, M. R., & McMurry, P. H. (2008). Equations Governing Single and Tandem DMA Configurations and a New Lognormal Approximation to the Transfer Function. Aerosol Science and Technology, 42(6), 421-432. doi:10.1080/02786820802157823

Stratton, K., Shetty, P., Wallace, R., & Bondurant, S. (Eds.). (2001). Clearing the Smoke: Assessing the Science Base for Tobacco Harm Reductiono Title. Washington, D.C.: National Academies Press.

Tang, X., Zheng, Z., Jung, H. S., & Asa-Awuku, A. (2012). The Effects of Mainstream and Sidestream Environmental Tobacco Smoke Composition for Enhanced Condensational Droplet Growth by Water Vapor. Aerosol Science and Technology, 46(7), 760-766. doi:10.1080/02786826.2012.663949

U.S. Department of Health and Human Services. (2010). How Tobacco Smoke Causes Disease: The Biology and Behavioral Basis for Smoking-Attributable Disease: A Report of the Surgeon General.

U.S. Department of Health and Human Services. (2012). [Docket No. FDA-2012-N-0143] Harmful and Potentially Harmful Constituents in Tobacco Products and Tobacco Smoke; Established List.

University of Kentucky. (2014). Reference Cigarette Program. Retrieved December 8, 2014, from http://www2.ca.uky.edu/refcig/

Vlasenko, S. S., & Mikhailov, E. F. (2013). Tandem of Differential Mobility Analyzer and Centrifugal Particle Mass

Analyzer: application to hygroscopic growth of aerosol particles. Prague, Czech Republic, September 1-6, 2013: European Aerosol Conference (EAC).

Xi, J., Kim, J., Si, X. A., & Zhou, Y. (2013). Hygroscopic aerosol deposition in the human upper respiratory tract under various thermo-humidity conditions. Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering, 48(14), 1790-1805. doi:10.1080/10934529.2013.823333

Zhang, Z., Kleinstreuer, C., & Hyun, S. (2012). Size-change and deposition of conventional and composite cigarette smoke particles during inhalation in a subject-specific airway model. Journal of Aerosol Science, 46(0), 34-52. doi:http://dx.doi.org/10.1016/j.jaerosci.2011.12.002

Figure Captions:

Figure 1: TDMA experimental setup used to measure the electrical mobility diameter growth of the particles, where PG is the gauge pressure, FC is a flow controller, TC is a temperature controller and HT is a heating tape. TW is a three way valve, CO is a critical orifice, VP is a vacuum pump and CC is a cooling coil. RH1, RH2 and RH3 were SHT75 RH sensors, while RH4 was a MBW-973 hygrometer.

Figure 2: DMA-CPMA experimental setup used to measure the mass growth of the particles, where PG is the gauge pressure, FC is a flow controller, TC is a temperature controller, and HT is a heating tape. TW is a three way valve, CO is a critical orifice, VP is a vacuum pump, and CC is a cooling coil. RH1 to RH3 and RH5 were SHT75 RH sensors.

Figure 3: Hygroscopic mobility diameter growth from a dry state (<25% RH) of d2,DRY=236.3 ± 8.8 nm particles produced by a University of Kentucky 3R4F cigarette smoked following HCI puffing parameters.

Figure 4: Hygroscopic mobility diameter growth of (A) ~100 nm and (B) ~240 nm mainstream smoke particles.

Figure 5: Hygroscopic mobility diameter growth from a dry state (<25% RH) of three different particle sizes produced by a University of Kentucky 3R4F cigarette smoked following HCI puffing parameters.

Figure 6: Hygroscopic mobility diameter growth from a dry state (<25% RH) of particles produced by a University of Kentucky 3R4F (d2,DRY= 236.3 ± 8.8 nm) or 1R5F (d2, dry=233.7 ± 11.1 nm) cigarette smoked following HCI puffing parameters.

Figure 7: Hygroscopic mass growth from a dry state (<25% RH) of d1 ,dry=258.2 ± 7.8 nm particles produced by a University of Kentucky 3R4F cigarette smoked following HCI puffing parameters.

Figure 8: Hygroscopic mass growth (dt dry=258.2 ± 7.8 nm) compared against volume growth (d1)DRY=255.3 ± 7.7 nm) of particles produced by a University of Kentucky 3R4F cigarette smoked following HCI puffing parameters, where the dotted line is the density growth factor calculated from

the shown mass and volume fits and the shaded region represents its uncertainty due to the range of possible sample RHs within the CPMA.

Table Captions:

Table 1: Characteristics of the tested reference cigarettes. Reported 'Tar' (or NFDPM - Nicotine Free Dry Particulate Matter) and Nicotine yields determined under ISO smoking conditions (ISO3308:2012, 2012; University of Kentucky, 2014).

Cigarette Circumference (mm) Length (mm) 'Tar' (NFDPM) (mg/cig) Nicotine (mg/cig) Water (mg/cig) % Tip ventilation

3R4F 24.8 84 9.4 0.73 0.9 30

1R5F 24.7 83.9 1.7 0.16 0.3 69

• The maximum mobility growth factor measured was 1.27 at 96% RH

• The maximum mass growth factor measured was 1.53 at 93.7% RH

• Particle size had a small effect on growth, that increased as RH increased

• As RH increased, particle mass grew at a faster rate than particle volume

• At least a portion of the particle composition was water soluble

EC4]--

H T4; ""=l (54)

Hu m midif ier 4

H i T3i n®

Hu ÈËÈÈN f midifier 3

0.6 LPM

Exhaust

Legend

Sample Line Control Feedback

3 LPM DMA 2

0.3 LPM

►CPC 2—^Exhaust

HEPA__i

Filter 3 ^

Dryer 2

Exhaust

CC2 RH

C02 I VP2

Exhaust 0.3 LPM

0.3 LPM

Exhaust

'—^Exhaust

(Pg=0.5 bar)

HEPA Filter 1

Tedlar® yBag y

[M]---,

Humidifier 1

FCI^O-

Dryer 1

1.5 LPM

(RH)—

Exhaust

H 1 T3 ©

Hu ÈÈÈÈN f midifier 3

1.5 LPM

Humidifier 2

Dryer 2

HEPA Filter 2

¡1—^VP1—^Exhaust C01

Exhaust

Legend

Sample Line Control Feedback

CC2 RH

1.5 LPM

CPC 1 t

Exhaust

o 1.20

1.15 1.10 1.05 1.00 0.95

90 100

Relative Humidity in DMA 2,RH4 (%)

o 1.25

a LL 1.20

Ô 1.10

i 1.05

o M 1.00

This Study

Ishizu et al. (1980) Data

-Ishizu et al. (l98o) Model

.........Longest and Xi (2008)

90 100

Relative Humidity in DMA 2,RH4 (%)

2.05 1.95 1.85

1.75 1.65 1.55 1.45 1.35 1.25 1.15 1.05

This Study

Li and Hopke (1993)

Robinson and Yu (1998)

Relative Humidity in DMA 2,RH4 (%)

< d2,DRY= =95.2 ± 3.0 nm □ .

o d2,DRY= =236.3 ± 8.8 nm O -

□ C2,DRY= =371.1 ± 11.7 nm o "

90 100

Relative Humidity in DMA 2,RH4 (%)

o 1.05

Relative Humidity in DMA 2,RH4 (%)

o 1.45

a Ll_ 1.35

si 1.25

O 1.15

a M 1.05

O This Study Ishizu et al. (1980) Data _ Ishizu et al. (1980) Model

60 65 70 75 80 85 90 95 100

Relative Humidity in CPMA,RHcpma (%)

70 75 80 85 90 95

Relative Humidity, RH (%)