Measuring aerosol size distributions with the aerodynamic aerosol classifier

Figures & data

Figure 1. Tandem AAC experimental setup used to characterize AAC transfer function.

Figure 2. AAC-CPC system used to measure the aerodynamic size distribution of an aerosol. This system was validated by comparing against ELPI, SMPS, and CPC measurements in parallel.

Figure 3. Different theoretical representations of the balanced flow AAC transfer function (TF), where the non-diffusing (ND) and diffusing (D) transfer functions were developed by Tavakoli and Olfert (2013) and the log-normal (Log) transfer functions were developed following Stolzenburg and McMurry (2008). The diffusing transfer functions shown represent an AAC setpoint equivalent to a 75 nm particle mobility diameter.

Figure 4. Idealized (Equation (3[3] )) and non-idealized (Equation (7[7] )) balanced flow AAC transfer function.

Figure 5. AAC transfer function characterization, where LF: in L/min and HF: in L/min.

Table 1. Fitted coefficients to estimate transfer function broadening as function of particle size.

Instrument	a	b	c
AAC LF	−1.201	−0.2387	0.9244
AAC HF	1.056e-05	1.181	0.4923
AAC All	−1.73	−0.0316	1.999
DMA (Birmili et al. 1997)	−11.05	−1.739	0.9956

Figure 6. Corrected SMPS and AAC characterization of the same aerosol sources.

Table 2. Comparison of mobility size distributions measured by SMPS (corrected for multiple-charging), and AAC (converted using known effective density) in parallel. The direct AAC-CPC systems measurements (denoted as Raw) were corrected for transfer function losses and broadening (denoted by NI).

Aerosol source	AAC	CMD (nm)	GSD		% Difference from SMPS and CPC
	flow			(× 10^4 cm^−3)	CMD	GSD
DOS Constant	LF-Raw	259.5	1.93	1.37	5.4%	−2.2%	−28.6%
	LF-NI	250.2	1.97	1.88	1.6%	0.1%	−2.3%
DOS Collison	LF-Raw	318.8	1.87	2.33	4.1%	−4.6%	−20.2%
	HF-Raw	312.2	1.87	2.28	1.9%	−4.6%	−22.0%
	LF-NI	311.5	1.90	3.12	1.7%	−3.5%	6.6%
	HF-NI	310.2	1.88	2.90	1.3%	−4.5%	−0.9%
702 Constant	LF-Raw	292.4	1.70	1.13	7.9%	−5.2%	−25.6%
	HF-Raw	283.7	1.72	1.13	4.7%	−4.4%	−25.7%
	LF-NI	287.0	1.73	1.52	5.9%	−4.0%	−0.1%
	HF-NI	282.2	1.72	1.44	4.1%	−4.4%	−5.5%

Figure 7. Corrected AAC (NI) and ELPI characterization of the same aerosol source.

Table 3. Comparison of aerodynamic size distributions measured by ELPI and AAC (corrected for transfer function losses and broadening, denoted as NI) in parallel.

Aerosol source	AAC	CMD (nm)	GSD		% Difference from SMPS and CPC
	flow			(× 10^4 cm^−3)	CMD	GSD
DOS Constant	LF-NI	277.5	1.85	2.55	−14.1%	7.2%	22.4%
	HF-NI	264.3	1.86	2.38	−18.2%	7.7%	14.3%

Tavakoli, F., and Olfert, J. S. (2013). An Instrument for the Classification of Aerosols by Particle Relaxation Time: Theoretical Models of the Aerodynamic Aerosol Classifier. Aerosol Sci. Technol., 47(8):916–926.

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Stolzenburg, M. R., and McMurry, P. H. (2008). Equations Governing Single and Tandem DMA Configurations and a New Lognormal Approximation to the Transfer Function. Aerosol Sci. Technol., 42(6):421–432.

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Birmili, W., Stratmann, F., Wiedensohler, A., Covert, D., Russell, L. M., and Berg, O. (1997). Determination of Differential Mobility Analyzer Transfer Functions Using Identical Instruments in Series. Aerosol Sci. Technol., 27(2):215–223.

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