Development of a cloud condensation nuclei (CCN) counter using a laser and charge-coupled device (CCD) camera

Abstract

A continuous flow streamwise thermal gradient cloud condensation nuclei (CCN) counter with an aerosol focusing and a laser-charge-coupled device (CCD) camera detector system was developed here. The counting performance of the laser-CCD camera detector system was evaluated by comparing its measured number concentrations with those measured with a condensation particle counter (CPC) using polystyrene latex (PSL) and NaCl particles of varying sizes. The CCD camera parameters (e.g. brightness, gain, gamma, and exposure time) were optimized to detect moving particles in the sensing volume and to provide the best image to count them. The CCN counter worked well in the particle number concentration range of 0.6–8000 #·cm^-3 and the minimum detectable size was found to be 0.5 μm. The supersaturation in the CCN counter with varying temperature difference was determined by using size-selected sodium chloride particles based on Köhler equation. The developed CCN counter was applied to investigate CCN activity of atmospheric ultrafine particles at 0.5% supersaturation. Data showed that CCN activity increased with increasing particle size and that the higher CCN activation for ultrafine particles occurred in the afternoon, suggesting the significant existence of hygroscopic or soluble species in photochemically-produced ultrafine particles.

Keywords

aerosol / cloud condensation nuclei (CCN) counter / ultrafine particle

References

[1] IPCC. Climate Change 2007: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007

[2] Twomey S A, Piepgrass M, Wolfe T L. An assessment of the impact of pollution on global cloud albedo. Tellus. Series B, Chemical and Physical Meteorology, 1984, 36B(5): 356–366

[3] Schulz M, Textor C, Kinne S, Balkanski Y, Bauer S, Berntsen T, Berglen T, Boucher O, Dentener F, Guibert S, Isaksen I S A, Iversen T, Koch D, Kirkevåg A, Liu X, Montanaro V, Myhre G, Penner J E, Pitari G, Reddy S, Seland Ø, Stier P, Takemura T. Radiative forcing by aerosols as derived from the AeroCom present-day and pre-industrial simulations. Atmospheric Chemistry and Physics, 2006, 6(12): 5225–5246

[4] Kohler H. The nucleus in and the growth of hygroscopic droplets. Transactions of the Faraday Society, 1936, 32: 1152–1161

[5] Pruppacher H R, Klett J D. Microphysics of Clouds and Precipitation. Dordrecht: Kluwer Academic Pub, 1997

[6] Cruz C N, Pandis S N. A study of the ability of pure secondary organic aerosol to act as cloud condensation nuclei. Atmospheric Environment, 1997, 31(15): 2205–2214

[7] Sun J, Ariya P A. Atmospheric organic and bio-aerosols as cloud condensation nuclei (CCN): A review. Atmospheric Environment, 2006, 40(5): 795–820

[8] Twomey S. Measurements of natural cloud nuclei. Journal de Recherches Atmosphériques, 1963, 1: 101–105

[9] Sinnarwalla A, Alofs D. A cloud nucleus counter with Long available growth time. Journal of Applied Meteorology, 1973, 12(5): 831–835

[10] Lala G, Jiusto J. An automatic light scattering CCN counter. Journal of Applied Meteorology, 1977, 16(4): 413–418

[11] Fukuta N, Saxena V. A horizontal thermal gradient cloud condensation nucleus spectrometer. Journal of Applied Meteorology, 1979, 18(10): 1352–1362

[12] Hudson J G. An instantaneous CCN spectrometer. Journal of Atmospheric and Oceanic Technology, 1989, 6(6): 1055–1065

[13] VanReken T M, Nenes A, Flagan R C, Seinfeld J H. Concept for a new cloud condensation nucleus (CCN) spectrometer. Aerosol Science and Technology, 2004, 38(7): 639–654

[14] Lance S, Medina J, Smith J, Nenes A. Mapping the operation of the DMT continuous flow CCN counter. Aerosol Science and Technology, 2006, 40(4): 242–254

[15] Sinnarwalla A, Alofs D, Carstens J. Measurement of growth rate to determine condensation coefficients for water drops grown on natural cloud nuclei. Journal of the Atmospheric Sciences, 1975, 32(3): 592–599

[16] Chuang P Y, Nenes A, Smith J N, Flagan R C, Seinfeld J H. Design of a CCN instrument for airborne measurement. Journal of Atmospheric and Oceanic Technology, 2000, 17(8): 1005–1019

[17] Oliveira J C P, Vali G. Calibration of a photoelectric cloud condensation nucleus counter. Atmospheric Research, 1995, 38(1–4): 237–248

[18] Philippin S, Betterton E A. Cloud condensation nuclei concentrations in Southern Arizona: instrumentation and early observations. Atmospheric Research, 1997, 43(3): 263–275

[19] Giebl H, Berner A, Reischl G, Puxbaum H, Kasper-Giebl A, Hitzenberger R. CCN activation of oxalic and malonic acid test aerosols with the University of Vienna cloud condensation nuclei counter. Journal of Aerosol Science, 2002, 33(12): 1623–1634

[20] Rose D, Gunthe S, Mikhailov E, Frank G, Dusek U, Andreae M, Poschl U. Calibration and measurement uncertainties of a continuous-flow cloud condensation nuclei counter (DMT-CCNC): CCN activation of ammonium sulfate and sodium chloride aerosol particles in theory and experiment. Atmospheric Chemistry and Physics, 2008, 8(5): 1153–1179

[21] Corrigan C, Novakov T. Cloud condensation nucleus activity of organic compounds: a laboratory study. Atmospheric Environment, 1999, 33(17): 2661–2668

[22] Frank G P, Dusek U, Andreae M O. Technical note: characterization of a static thermal-gradient CCN counter. Atmospheric Chemistry and Physics, 2007, 7: 3071–3080

RIGHTS & PERMISSIONS

Higher Education Press and Springer-Verlag Berlin Heidelberg