Particle Size Distribution of E-Cigarette Aerosols and the Relationship to Cambridge Filter Pad Collection Efficiency

Transcription

1 Particle Size Distribution of E-Cigarette Aerosols and the Relationship to Cambridge Filter Pad Collection Efficiency S.L Alderman, C. Song, S. Moldoveanu, S.K. Cole R.J. Reynolds Tobacco Company, Winston-Salem, NC CORESTA SSPT Meeting, Seville, Spain September 29-October 03, 2013

2 Outline Particle size distribution measurements challenges common for tobacco burning and e-cigarette aerosol characterization Model predictions of filter efficiency 44 mm Cambridge filter Experimental results on Cambridge pad collection efficiency/vapor-particle partitioning PG, GLY, NIC, WAT Conclusions

3 Challenges associated with cigarette smoke aerosol characterization MSS is a dynamic aerosol and particle size changes rapidly due to coagulation particles/cm 3 results in rapid coagulation measured number concentration will be lower than and average particle size will be larger than filter exit size due to aging/coagulation prior to measurement dilution of aerosol can greatly minimize effects of coagulation Coagulation the process where particles collide with one another due to relative motion between them and adhere to form larger particles.

4 Challenges associated with cigarette smoke aerosol characterization MSS particulate matter contains components over a range of volatilities some saturated in the vapor phase Dilution of the aerosol is common not only to minimize coagulation, but to lower particle number concentration below operational limits of many types of instruments will shift particle-vapor equilibrium and result in evaporation of some particulate matter components, results in under reporting of true filter exit particle size

5 Aerosol Mass/Gravimetric Mass Aerosol property mass vs. Cambridge filter mass Reliability of aerosol measurements can be assessed by comparing particulate mass based on measured properties to gravimetric filter collected TPM mass particle size, number, spread of distribution and density r² = 0.91 Eclipse Water Fraction of TPM Mass originally present in particulate phase (and captured by filter pad) evaporates under high dilution leading to erroneously small particle size measurements, thus mass calculated from size parameters is biased low Alderman S.L. and Ingebrethsen, B.J. (2011) Characterization of Mainstream Cigarette Smoke Particle Size Distributions from Commercial Cigarettes using a DMS500 Fast Particulate Spectrometer and Smoking Cycle Simulator. Aerosol Sci. Technol., 44:

6 E-cigarette Terminology Vapor is often used to describe the effluent from e-cigarettes this terminology appears commonplace among e-cigarette users (vapers) can be found in numerous scientific documents This is a technical inaccuracy the output from an e-cigarette is accurately described as an aerosol, which is composed of a particulate phase dispersed in a gaseous medium. some components of the e-liquid are expected to exist at some level in a true, non-condensed vapor phase This distinction will need to be made clear to avoid confusion when discussing issues such as particle/vapor partitioning of e-cigarette aerosols.

7 Particle Size Distribution of E-cigarette Aerosol Measurements made in undiluted state by spectral transmission and after high dilution with DMS500 electric mobility analysis measures wavelength dependence of transmitted light through aerosol (Mie scattering) Ingebrethsen, B.J., Cole, S.K. and Alderman, S.L. (2012) Electronic Cigarette Aerosol Particle Size Distribution Measurements. Inhalation Toxicology 24: Main findings were: E-cigarette aerosols undergo nearly complete evaporation under high dilution more so than burn-down aerosols Spectral transmission procedure showed e-cig particle sizes and number densities very similar to tobacco burning aerosols

8 Particle Size Distribution of E-cigarette Aerosol representative results 55 ml puff volume, 2 sec puff duration, square wave shape, puff 5 for 3R4F Count Median Diameter (nm) Spec. Ext. (no dilution) DMS500 (high dilution) 3R4F 228 ± ± 8* E-Cig A 296 ± ± 0.68 E-Cig B 238 ± ± 3.1 *207 nm after evaporation correction

9 Particle Size Distribution of E-cigarette Aerosol representative results 55 ml puff volume, 2 sec puff duration, square wave shape, puff 5 for 3R4F Particle Number Concentration (per cm 3 x10 9 ) Spec. Ext. (no dilution) DMS500 (high dilution) 3R4F 2.75 ± ± 0.32 E-Cig A 1.8 ± ± 1.26 E-Cig B 1.56 ± ± 1.98

10 Particle Size Distribution of E-cigarette Aerosol representative results 55 ml puff volume, 2 sec puff duration, square wave shape, puff 5 for 3R4F Aerosol and Cambridge Pad Mass (mg/puff) Spec. Ext. (no dilution) Cambridge Pad DMS500 (high dilution) 3R4F 1.52 ± ± ± 0.20 E-Cig A 2.4 ± ± ± E-Cig B 0.95 ± ± ± 0.005

11 Cambridge Pad Collection of E-cig Aerosols Some likely inaccurate reports of e-cig particle size distributions combined with a common misunderstanding of particle capture by fibrous filters has raised some questions on the suitability of Cambridge pads for sampling these aerosols A theoretical filtration model is presented with filter properties taken from a 44 mm Cambridge pad filter diameter, thickness, fiber diameter and length, fiber volume fraction, flow rate (face velocity), and particle size all have an influence

12 Filtration Efficiency (%) Cambridge Filter Single Fiber Collection Efficiencies at 27.5 cm 3 /s Impaction Interception Diffusion + Interception Diffusion Total of all Mechanisms Particle Size (nm) Diffusion and Interception dominate Overall efficiency near 100% for all sizes

13 Filtration Efficiency (%) Filtration Dependence on Flow Rate Particle Size (nm) Most penetrating particle size shifts to lower sizes as flow rate increase (~550 to 350 nm), but is still >99% captured at 50 cm 3 /s 10 cc/s 17.5 cc/s 27.5 cc/s 35 cc/s 50 cc/s Illustrates that fibrous filters do not act as microscopic sieves Predictions only for particles, some components of interest may exist in vapor phase and pass through Cambridge filter

14 Efficiency of Cambridge Filters for Collection of Primary E-cig Aerosol Former Components Experimental Two commercially available e-cigarettes E-cig A ~ 12% PG, 70% GLY, 4.5% NIC, 14% water E-cig B ~ 50% PG, 48% GLY, 1.6% NIC, 1.8% water Both rechargeable cartomizer types A Cerulean SM 450 smoking machine was used to generate square wave puffs of varying volume 55 or 75 ml volume, square wave shape, 3 s duration, 30 s interval 20 or 80 puffs collected per sample E-cig aerosol was subjected to standard Cambridge filter (44 mm) collection A trap intended to capture any material passing through the filter was placed immediately downstream of the filter. ORBO -32 Small trap containing charcoal in two sections (A and B) An XAD-4 trap was used under the 75 ml puff volume/80 puffs collected test variant (porous highly cross-linked polystyrene/divinylbenzene copolymer) 60% R.H. and 24 ºC conditions.

15 Filter and Trap Analysis Following extraction, Cambridge filter and vapor adsorbent trap samples were analyzed by GC FID for PG, GLY & NIC The same extraction solutions were used for quantitation of water by GC TCD (water corrected for solvent, pad, and trap background content) Quantitative analysis of pad and vapor trap allows determination of Cambridge pad filter efficiency provided that each component was completely captured on either the filter pad or downstream vapor trap all material was effectively extracted from each sample matrix and accounted for by GC analysis. Analysis of a secondary vapor trap (Section B) revealed no presence of GLY or NIC, and only relative traces of PG and water

16 Cambridge Filter Efficiency - Results Flow Rate cm 3 /s Puffs Analyte 25 ORBO 80 Ecig A Ecig A Ecig B % on Pad % on Trap % on Pad GLY NIC PG WAT Ecig B % on Trap GLY, PG, and NIC captured with good efficiency on Cambridge filter partitioning between the Cambridge filter and adsorbent trap and aligned with each component s partial vapor pressure consistent trends for E-cig A and E-Cig B Water fraction captured on Cambridge filter is highly variable

17 Cambridge Filter Efficiency - Results Flow Rate cm 3 /s Puffs Analyte Ecig A % on Pad Ecig A % on Trap Ecig B % on Pad Ecig B % on Trap GLY NIC PG WAT GLY NIC PG WAT GLY NIC PG WAT GLY NIC PG WAT GLY * *0.001 NIC * *0.574 PG * *1.229 WAT * *2.200 * Indicates XAD-4 trap. All other trap values correspond to ORBO

18 Cambridge Filter Efficiency - Results % cartridge mass loss captured as TPM % TPM (pad) mass accounted for by GC analysis Flow Rate cm 3 /s Puffs E-cig A 97 ± B 105 ± A 95 ± B 103 ± A 98 ± B 107 ± A 99 ± B 105 ± A 96 ± (XAD) B 103 ± (XAD) For E-cig A more material exits cartridge during puffing than was captured on Cambridge pad as TPM. Opposite trend for E-Cig B in-cartridge e-liquid water content influences uptake of ambient water during testing (14% for e-cig A, ~ 2% for E-cig B) hygroscopicity of GLY and PG GC analysis of pad accounts for about reasonable amount of gravimetric mass

19 Conclusions Characteristics of e-cigarette aerosols, i.e. high particle number density and particulate matter that can evaporate under high dilution conditions will generally complicate PSD measurements Measurements made by a spectral transmission procedure under non-diluting conditions suggest that the average particle size and number concentration of e-cigarette aerosols are comparable to those of tobacco burning cigarette aerosols. Results of a model-based Cambridge pad filtration efficiency study predict near 100% capture of particles of a size consistent with those found in e-cigarette size aerosols.

20 Conclusions Results of an experimental study indicate PG, GLY, and NIC are efficiently captured on Cambridge pads, suggesting that these components largely reside in the condensed, particulate phase of the aerosol. Information on the particle/vapor partitioning of water was largely inconclusive and may indicate that the vapor traps employed for this study are not suitable for water analyses. All of the above areas of study need further exploration

21 Acknowledgment Susan Pike Buddy Mills Co-Authors