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

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 Combining double low line 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 0.2-1.0μm size range. Under dry conditions, the higher mass fraction of particles in the 0.2-1.0μm 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, Combining double low line 550nm, the extinction coefficient from the 0.01-0.2, 0.2-0.5, and 1.0-2.0μm size ranges increased significantly with the increase in RH, whereas the extinction contributions from the 0.5-1.0 and 2.0-10.0μm size ranges to the extinction coefficient decreased slightly.