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Volume 11, issue 2 | Copyright
Atmos. Meas. Tech., 11, 895-906, 2018
https://doi.org/10.5194/amt-11-895-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Feb 2018

Research article | 14 Feb 2018

A new method for calculating number concentrations of cloud condensation nuclei based on measurements of a three-wavelength humidified nephelometer system

Jiangchuan Tao1,2, Chunsheng Zhao2, Ye Kuang1,2, Gang Zhao2, Chuanyang Shen2, Yingli Yu2, Yuxuan Bian3, and Wanyun Xu3 Jiangchuan Tao et al.
  • 1Institute for Environment and Climate Research, Jinan University, Guangzhou, China
  • 2Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China
  • 3State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China

Abstract. The number concentration of cloud condensation nuclei (CCN) plays a fundamental role in cloud physics. Instrumentations of direct measurements of CCN number concentration (NCCN) based on chamber technology are complex and costly; thus a simple way for measuring NCCN is needed. In this study, a new method for NCCN calculation based on measurements of a three-wavelength humidified nephelometer system is proposed. A three-wavelength humidified nephelometer system can measure the aerosol light-scattering coefficient (σsp) at three wavelengths and the light-scattering enhancement factor (fRH). The Ångström exponent (Å) inferred from σsp at three wavelengths provides information on mean predominate aerosol size, and hygroscopicity parameter (κ) can be calculated from the combination of fRH and Å. Given this, a lookup table that includes σsp, κ and Å is established to predict NCCN. Due to the precondition for the application, this new method is not suitable for externally mixed particles, large particles (e.g., dust and sea salt) or fresh aerosol particles. This method is validated with direct measurements of NCCN using a CCN counter on the North China Plain. Results show that relative deviations between calculated NCCN and measured NCCN are within 30% and confirm the robustness of this method. This method enables simplerNCCN measurements because the humidified nephelometer system is easily operated and stable. Compared with the method using a CCN counter, another advantage of this newly proposed method is that it can obtain NCCN at lower supersaturations in the ambient atmosphere.

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Existing chamber technologies for direct measurements of number concentration of cloud condensation nuclei (NCCN) are sophisticated and expensive. In this paper, a new method is proposed to calculate NCCN based only on measurements of a humidified nephelometer system which have accounted for influences of both aerosol size and aerosol hygroscopicity on NCCN calculation. This new method makes NCCN measurements more convenient and is capable of obtaining NCCN at lower supersaturations.
Existing chamber technologies for direct measurements of number concentration of cloud...
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