Articles | Volume 17, issue 6
Research article
28 Mar 2017
Research article |  | 28 Mar 2017

Analysis of extinction properties as a function of relative humidity using a κ-EC-Mie model in Nanjing

Zefeng Zhang, Yan Shen, Yanwei Li, Bin Zhu, and Xingna Yu

Abstract. The relationship between relative humidity (RH) and extinction properties is of widespread concern. In this study, a hygroscopic parameter (κ) and the volume fraction of elemental carbon (EC) were used to characterize the chemical characteristics of particles, and a core-shell model was built based on these characteristics. The size distribution, chemical composition, and RH were measured in Nanjing from 15 October to 13 November 2013. The model-derived extinction coefficients of particles were fit with the program of coated spheres according to Bohren and Huffman (2008) (BHCOAT), and the modeled values correlated well with the measurement-derived extinction coefficients (r2 = 0. 81), which suggested that the core-shell model produced reasonable results. The results show that more than 81 % of the extinction coefficient in Nanjing was due to particles in the 0.2–1.0 µm size range. Under dry conditions, the higher mass fraction of particles in the 0.2–1.0 µm size range caused the higher extinction coefficient. An increase in RH led to a significant increase in the extinction coefficient, although the increases differed among the different size segments. For λ = 550 nm, the extinction coefficient from the 0.01–0.2, 0.2–0.5, and 1.0–2.0 µm size ranges increased significantly with the increase in RH, whereas the extinction contributions from the 0.5–1.0 and 2.0–10.0 µm size ranges to the extinction coefficient decreased slightly.

Short summary
Aerosol particles and relative humidity are the main factors that affect atmospheric visibility. Due to the complexity of the physicochemical properties of aerosol particles, more and more instruments and cost were put into research, which limited the development of large area observation research. Thus, it is especially important to find the key parameters which affect the visibility and to establish the observation scheme.
Final-revised paper