Effect of Working Fluid on Sub-2 nm Particle Detection with a Laminar Flow Ultrafine Condensation Particle Counter

Figures & data

FIG. 1 Schematic of the domains where the temperature and vapor concentration inside the UCPC are simulated.

FIG. 2 The frequency distribution of the 50% activation sizes (D _p50) of 863 organic compounds (Yaws 1999). These results apply to all compounds from that compilation that have melting and boiling points below 20°C and 60°C, respectively.

FIG. 3 The calculated 50% activation size, D _p50, versus the surface tension evaluated at the temperature equal to the average of the saturator and condenser temperatures.

FIG. 4 (a) The calculated saturation ratio (b) the calculated 50% activation size, D _p50, versus the saturation vapor pressure where the saturation ratio is the highest along the axis of the condenser.

FIG. 5 Simulated activation efficiencies of the Ultrafine CPC for selected working fluids.

TABLE 1 Physical/chemical properties of the potential working fluids and parameters describing the performance of UCPC

	Units	n-butanol	Diethylene Glycol	DOS	Oleic Acid	Ethylene Glycol	Propylene Glycol
CAS ^a Number		71-36-3	111-46-6	122-62-3	112-80-1	107-21-1	504-63-2
Molecular Weight	g/mol	74.123	106.1	426.7	282.5	62.1	76.1
Diffusion Coefficient	cm^2/s	0.0920	0.0849	0.0429	0.0471	0.108	0.102
Surface Tension	dyne/cm	25.0	47.2	30.9	30.4	48.3	45.0
Freezing Point ^b	°C	−84	−10.4	−48	13.4	−12.7	−27.7
Boiling point ^b	°C	117	246	256	360	197.3	214.4
Viscosity at 20°C	centi-poise	2.6	38.3	23 ^c	34.1	21.8	28.1
Solubility ^b		s H2O, bz; msc EtOH, eth; vs ace	s H2O, EtOH, eth, chl	vs ace, bz, EtOH	i H2O; msc EtOH, eth, ace, bz, chl, ctc	msc H2O, EtOH,ace s eth, chl; sl bz	msc H2O, EtOH; vs eth; sl bz
Saturator Temperature	°C	47.9	74.5	128	93.4	58.4	68.7
Condenser Temperature	°C	10	10	10	13.4	10	10
Peak Super Saturation (S)	—	4.37	88.5	504000	10100	13.0	21.5
Location of Peak S	cm	4.4	5.5	7.68	7.3	4.7	4.45
Partial vapor pressure at Peak S	atm	2.01 × 10^−2	2.03 × 10^−4	1.59 × 10^−6	1.37 × 10^−6	6.4 × 10^−4	5.61 × 10^−4
50% Cutoff D P Kelvin/Thomson	nm	2.89/2.64	1.88/1.42	1.90/N/A ^d	1.90/1.71	1.94/1.63	1.97/1.71

FIG. 6 Simulated droplet sizes along the axis of CPC condenser.

FIG. 7 Aerosol generation system for evaluating the activation efficiency of the CPC.

FIG. 8 Experimental setup for evaluating the activation efficiency of the Ultrafine CPC that uses various working fluids.

FIG. 9 Flow schematic of the ultrafine condensation particle counter, UCPC, and downstream TSI 3010 CPC.

TABLE 2 The 50% cutoff size of activation curve for the working fluids investigated

				50% cutoff size of activation efficiency curve (nm)
						Material placed inside an evaporation tube
Working Fluids	Tsaturator/Tcondenser,°C	Peak saturation ratio	Partial pressure at peak, atm	Kelvin diameter, nm	Polarity	NaCl	(NH4)2SO4	Ag
diethylene glycol	50.2/10.0	17.0	3.6 × 10^−5	3.0	Positive	[1.7] (1.3) ± 0.06 ^a	[1.7] (1.3) ± 0.01	[2.0] (1.6) ± 0.05
					Negative	[< 1.2] (< 0.8) ^b	[1.4] (1.0) ± 0.06	[2.0] (1.5) ± 0.03
ethylene glycol	46.0/10.0	6.41	3.0 × 10^−4	2.7	Positive	[1.8] (1.5) ± 0.11	[1.8] (1.4) ± 0.01	[2.5] (2.0) ± 0.02
					Negative	[1.3] (1.0) ± 0.09	[1.5] (1.1) ± 0.05	[2.1] (1.7) ± 0.01
propylene glycol	40.0/10.0	4.36	9.77 × 10^−5	4.1	Positive	[2.0] (1.5) ± 0.05	[1.9] (1.5) ± 0.02	[2.9] (2.4) ± 0.10
					Negative	[1.7] (1.3) ± 0.10	[1.7] (1.3) ± 0.05	[2.5] (2.0) ± 0.03
oleic acid	64.1/16.4	340	7.4 × 10^−8	3.0	Positive	[1.7] (1.2) ± 0.01	[1.8] (1.4) ± 0.01	[2.0] (1.6) ± 0.02
					Negative	[1.2] (0.8) ± 0.05	[1.5] (1.2) ± 0.1	[1.9] (1.5) ± 0.01
DOS	99/31	1620	1.4 × 10^−7	3.1	Positive	[2.0] (1.5) ± 0.04	[2.3] (1.8) ± 0.11	[1.9] (1.5) ± 0.01
					Negative	[1.8] (1.4) ± 0.03	[2.2] (1.8) ± 0.02	[2.0] (1.6) ± 0.01

FIG. 10 Measured activation efficiencies η of positively (left) and negatively charged (right) particles using diethylene glycol as working fluid and test aerosols generated from (a) silver, (b) ammonium sulfate, and (c) sodium chloride.

FIG. 11 Measured activation efficiencies η of positively charged (left) and negatively charged (right) particles using oleic acid as working fluid and test aerosols generated from (a) silver (b) ammonium sulfate and (c) sodium chloride.

FIG. 12 Activation efficiencies η of ethylene glycol as a function of electrical mobility. The data were obtained by using test aerosols generated from sodium chloride. Mobility distributions of positive and negative ions generated from the aerosol charger are superimposed to illustrate the overlapping size range between ions and particles.

FIG. 13 The activation efficiencies versus time for detecting 2.3 nm (a) positively charged silver particles using ethylene glycol and (b) negatively charged silver particles using propylene glycol as working fluid.

FIG. A1 Schematic of an approach for achieving nanoparticle activation and growth within a single laminar flow tube.

FIG. A2 The simulated droplet growth within growth activator and booster using the setup shown in Figure A.1 as model input. The growth curve of n-butanol already shown in Figure 5 is also given as a reference.

FIG. B1 Detailed schematics of the experimental setup for evaluating the activation efficiency of the Ultrafine CPC using (a) Nano-DMA as mobility classifier and the (b) UCPC and FCE as detectors

TABLE B1 Description of theoretically accounted diffusion losses through transport within the experimental setup

> Segment in Figure B1	Assumptions	Length, cm	Flowrate
A to B	Fully developed flow through a plane parallel channel	3.2	1.5 LPM
B to C	Fully developed flow through a tube	6.4	1.5 LPM
C to D	Fully developed flow through a tube	7.5	3.0 or 3.8 LPM
D to E	Fully developed flow through a tube	4.7	1.5 or 1.9 LPM
D to F	Core portion of a fully developed flow through a tube	22.9	Total: 1.5 or 1.9 LPM
			Core: 0.3 LPM
F to G	Core portion of a fully developed flow through a tube	4.2	Total: 0.3 LPM
			Core: 0.6-0.75 cm^3/s
G to H	Fully developed flow through a tube	1.42	0.6-0.75 cm^3/s

FIG. B2 Comparison of particle size distribution dN/dln D _p of negatively charged particles at Nano-DMA inlet slit calculated by formal inversion (Equation [B1]) and by monodisperse approximation (Equation [B3]).

FIG. B3 Concentration reaching Faraday cage electrometer (FCE) calculated from theoretical expression (Equation [B1]) using particles size distributions obtained by formal inversion and monodisperse approximation shown in Figure B2. Experimentally measured concentrations are also given to show the goodness of fit.

FIG. B4 Comparison of activation efficiency η obtained by the monodisperse approximation (Equation [B6]), the formal inversion of Stolzenburg (Equations [B1] and [B2]), and the simplified approach introduced in this work (Equations [B4] and [B5]). The test particles are generated by evaporating the ammonium sulfate crystals.

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