Characterization of an Automated, Water-Based Expansion Condensation Nucleus Counter for Ultrafine Particles

Figures & data

FIG. 1 Dependence of Saturation ratio after expansion with temperature before expansion according to Equations (1) and (2) (solid curve). Kelvin diameter versus temperature before expansion for a given saturation ratio according to Equation (3) (dotted curve) for water.

FIG. 2 Schematic diagram of scattered light detection with the Expansion-CNC. Particles inside an expansion chamber scatter incoming laser light. The direct light beam and the scattered light in the forward direction between 0° and 1.1° are blocked. Scattered light that hits the annular area of a lens between 1.1° and 4.4° (shaded area) is collected and focused onto a photo diode detector.

FIG. 3 Diagram of the Expansion-CNC. The dotted rectangle depicts the optical part of the instrument that is usually covered by a light-absorbing box.

FIG. 4 Comparison of experimental (a) and theoretical (b) scattered light intensity. The vertical lines indicate the maximum and the minimum of the third step, respectively.

TABLE 1 Radius range at which a step can be observed and the corresponding average total and partial scattering cross section

Step	Radius range in μ m	Average total scattering cross section in cm^2	Average partial scattering cross section in cm^2
1st	0.8–1.2	7.68 · 10^−8	5.85 · 10^−9
2nd	1.8–2.2	2.92 · 10^−7	6.13 · 10^−8
3rd	2.7–3.3	6.37 · 10^−7	2.00 · 10^−7
4th	3.7–4.4	1.12 · 10^−6	3.82 · 10^−7

FIG. 5 Experimental set-up for comparison of the TSI UCPC and the Expansion-CNC.

FIG. 6 Comparison of measured and modeled curve for two different number concentrations. Modeled curve is calculated for monodisperse particles.

TABLE 2 Concentration ranges that can be measured with a certain step

Step	Concentration range in cm^−3
1st	34000–130000
2nd	800–34000
3rd	∼ 50–800
4th	∼ 50–800

FIG. 7 Comparison of measured and modeled curve for an extinction experiment. Observed and modeled ripple structures are in very good agreement. For clarity the modeled curve is shifted upwards by 0.003.

FIG. 8 Comparison of the number concentration measured by the Expansion-CNC and by the TSI UCPC for two lab-generated aerosol types.

FIG. 9 Comparison of the number concentration measured by the Expansion-CNC and by the TSI UCPC for ambient aerosol particles.

TABLE 3 Summarized characteristics of the Expansion-CNC

Number concentration range	50–130000 cm^−3
Lower size cut-off diameter	< 3.5 nm
Flow rate	0.3 liter/min quasi-continuous
Condensing fluid	Water
Sampling rate	∼ 0.1 Hz