Morphology and chemical characteristics of micro- and Nano-particles in the haze in Beijing studied by XPS and TEM/EDX

X-ray Photoelectron Spectroscopy (XPS) is a useful surface sensitive tool to explore the particulate matter with different particle sizes. In this work, we report the analysis of elemental species in particulate matter with size ranging from100 nm to 10 mu m during the autumn haze of 2014 in Beijing. The size dependence of element composition and chemical state distribution on the particle surface was investigated. It was found that the number of investigated element species decreased from 8 (at stage 2) to 4 (at stage 10) with the decrease of particle sizes down to 100 nm, which is in accordance with the result from Transmission electron microscopy (TEM/EDX) observations. Three chemical states of nitrogen, the amide group (399.9 eV), the ammoniumgroup (401.6 eV), and the nitrate group (407.2 eV), were confirmed according to the different binding energies. Nitrate was the main composition on the coarse particles, while the percentage of amide and ammonium at stage 3 (13.9% and 10.8% respectively) increased on the fine particles at stage 9 (46.8% and 38.8% respectively). The relative ratio of sulfate and ammonium(calculated 1: 1) in the fine particles suggests that there is no enough NH4+ to neutralize the sulfuric acid and the surface of the PMis acidic. The result is useful to investigate the generation processes and the sources of collected particles. (C) 2016 Elsevier B.V. All rights reserved.