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

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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

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Challenges associated with cigarette

smoke aerosol characterization

• MSS is a dynamic aerosol and particle

size changes rapidly due to coagulation 109-1010 particles/cm3 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.

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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

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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

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Water Fraction of TPM

Eclipse

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., 44:1409-1421.

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

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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.

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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 24:976-984.

• 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

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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 ± 13 184 ± 8*

E-Cig A 296 ± 19 14 ± 0.68

E-Cig B 238 ± 26 21 ± 3.1

*207 nm after

evaporation

correction

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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 cm3 x109)

Spec. Ext.

(no dilution)

DMS500

(high dilution)

3R4F 2.75 ± 0.91 3.88 ± 0.32

E-Cig A 1.8 ± 0.49 8.38 ± 1.26

E-Cig B 1.56 ± 0.72 11.8 ± 1.98

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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 ± 0.38 1.88 ± 0.32 1.31 ± 0.20

E-Cig A 2.4 ± 0.63 2.5 ± 0.28 0.0019 ± 0.0006

E-Cig B 0.95 ± 0.35 1.4 ± 0.20 0.010 ± 0.005

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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

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Cambridge Filter Single Fiber Collection

Efficiencies at 27.5 cm3/s

• Diffusion and Interception dominate

• Overall efficiency near 100% for all sizes

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Impaction

Interception

Diffusion + Interception

Diffusion

Total of all Mechanisms

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Filtration Dependence on Flow Rate

• Most penetrating particle size shifts to lower sizes as flow rate increase

(~550 to 350 nm), but is still >99% captured at 50 cm3/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

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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.

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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

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Cambridge Filter Efficiency - Results

Flow Rate

cm3/s Puffs Analyte

Ecig A

% on Pad

Ecig A

% on Trap

Ecig B

% on Pad

Ecig B

% on Trap

25

ORBO 80

GLY 99.999 0.001 100.00 0.000

NIC 99.869 0.131 99.892 0.108

PG 98.366 1.634 98.851 1.149

WAT 88.206 11.794 100.00 0.000

• 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

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Cambridge Filter Efficiency - Results

Flow Rate

cm3/s Puffs Analyte

Ecig A

% on Pad

Ecig A

% on Trap

Ecig B

% on Pad

Ecig B

% on Trap

25 80

GLY 99.999 0.001 100.00 0.000

NIC 99.869 0.131 99.892 0.108

PG 98.366 1.634 98.851 1.149

WAT 88.206 11.794 100.00 0.000

25 20

GLY 100.000 0.000 100.000 0.000

NIC 99.942 0.058 99.969 0.031

PG 98.941 1.059 99.343 0.657

WAT 51.146 48.854 100.00 0.000

18.3 80

GLY 100.000 0.000 100.000 0.000

NIC 99.915 0.085 99.923 0.077

PG 98.869 1.131 99.240 0.760

WAT 89.316 10.684 69.155 30.845

18.3 20

GLY 100.000 0.000 100.000 0.000

NIC 99.962 0.038 100.000 0.000

PG 99.377 0.623 99.503 0.497

WAT 46.818 53.182 20.608 79.392

25 80

GLY 99.999 *0.001 99.999 *0.001

NIC 99.409 *0.591 99.426 *0.574

PG 98.748 *1.252 98.771 *1.229

WAT 98.947 *1.053 97.800 *2.200 * Indicates XAD-4 trap. All other trap values correspond to ORBO

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Cambridge Filter Efficiency - Results

• 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

Flow Rate

cm3/s Puffs E-cig

% cartridge mass

loss captured as

TPM

% TPM (pad) mass

accounted for by GC

analysis

25 80 A 97 ± 0.29 96

25 80 B 105 ± 0.94 92

25 20 A 95 ± 5.1 89

25 20 B 103 ± 1.5 91

18.3 80 A 98 ± 5.3 95

18.3 80 B 107 ± 0.32 98

18.3 20 A 99 ± 15.1 84

18.3 20 B 105 ± 4.0 94

25 80 A 96 ± 1.6 97 (XAD)

25 80 B 103 ± 1.8 92 (XAD)

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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.

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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

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Acknowledgment

Susan Pike

Buddy Mills

Co-Authors

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