Methodology to quantify the ratio of multiple-to single-charged fractions acquired in aerosol neutralizers

Figures & data

Figure 1. Ratio of doubly to singly charged fractions as a function of mobility diameter calculated from the Fuchs charging model for ion properties suggested in different studies: [1] Reischl et al. (1996), [2] & [3] Adachi et al. (1985), [4] Porstendörfer et al. (1983) & Hussin et al. (1983), [5] Hoppel and Frick (1986), [6] Wiedensohler et al. (1986), [7] Hoppel and Frick (1990), [8] Wiedensohler and Fissan (1991), [9] Wiedensohler (1988) & ISO 15900 recommendation.

Figure 2. Schematic of the setup required for the application of the proposed methodology.

Figure 3. Simulated Tandem DMA response for a lognormal distribution with mean diameter of 80 nm and geometric standard deviation of 1.8, with the first DMA set to classify particles of 150 nm. The areas in different colors illustrate the contribution of different sized particles at each recorded peak. The dashed lines illustrate the integration limits defined in Equations 5a[5a] and 5b[5b] . Calculations were performed for the geometry of TSI 3081 DMA at sheath and sample flowrates of 3 and 0.3 lpm, respectively, and a total scan time of 300 s.

Figure 4. Error associated with the calculation of the ratio of double to single (black likes) and triple to single (grey lines) charge fractions through the integrals in Equations 4[4a] (solid lines) and 6 (dashed lines).

Table 1. Operating conditions and properties of the aerosols produced in the different particle generators employed in the study.

Aerosol	dg [nm]	σg [−]	Operating conditions
PAO	45	1.55	Vapours of PAO at 155°C carried by 1 lpm N2 and mixed with 10 lpm of N2 at ambient temperature.
DOS	70	1.40	Vapours of PAO at 155°C carried by 1 lpm N2 and mixed with 10 lpm of N2 at ambient temperature.
Soot #1 (miniCAST)	80	1.7	0.018 lpm C3H8, 0.8 lpm oxidation air, 1.5 lpm quench N2, and 2 lpm dilution air
Soot #2 (APG)	75	1.7	0.018 lpm C3H8, 0.53 lpm oxidation air, 2 lpm quench N2, and 5 lpm dilution air
Soot #3 (APG)	45	1.7	0.018 lpm C3H8, 0.84 lpm oxidation air, 2 lpm quench N2, and 5 lpm dilution air
Graphite #1	40	1.8	3 lpm N2, 3 lpm dilution air, 2 mA
Graphite #2	70	1.8	3 lpm N2, 3 lpm dilution air, 7 mA

Figure 5. Calculated ratios of double (upper panel) and triple (bottom panel) to single charged fractions from all experimental data collected using the ⁸⁵Kr sources. Each symbol corresponds to the average result from 2 to 6 scans. Different colors indicate results determined from tests conducted on different dates. The line corresponds to the regression fit by Wiedensohler (1988).

Table 2. Comparison of ratios of double- and triple to single charge fractions for Soot #1 after neutralization in a 85Kr (TSI 3077A) and a Soft X-ray (TSI 3088) bipolar charger.

	^85Kr		Soft X-ray		Difference
dB [nm]	φ^+2/φ^+1	φ^+3/φ^+1	φ^+2/φ^+1	φ^+3/φ^+1	φ^+2/φ^+1	φ^+3/φ^+1
70	0.092	0.002	0.113	0.003	23.0%	53.4%
103	0.190	0.015	0.228	0.022	19.9%	45.0%
125	0.269	0.032	0.292	0.037	8.8%	14.0%
155	0.326	0.058	0.398	0.088	21.9%	50.7%
309	0.526	0.213	0.664	0.328	26.4%	54.2%

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