Atmospheric particles exert influence on both human health and the environment. It is reported that many important climate-related chemical and physical processes occur at the particles surfaces. In this study, we collected size-segregated aerosol samples from different sources and analyzed the surface chemical compositions using both X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS).

First, two sets particles were collected at a coast site of Hong Kong in winter and summer. XPS was used to analyze both sets of the samples, which showed eight important surface elemental compositions: Mg, Na, Cl, N, S, Si, O, and C. Carbon was found to be the dominating surface element. The chemical states of C, N, and S were further examined....[ Read more ]

Atmospheric particles exert influence on both human health and the environment. It is reported that many important climate-related chemical and physical processes occur at the particles surfaces. In this study, we collected size-segregated aerosol samples from different sources and analyzed the surface chemical compositions using both X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS).

First, two sets particles were collected at a coast site of Hong Kong in winter and summer. XPS was used to analyze both sets of the samples, which showed eight important surface elemental compositions: Mg, Na, Cl, N, S, Si, O, and C. Carbon was found to be the dominating surface element. The chemical states of C, N, and S were further examined. The results indicated that the surface chemical properties of large size fractions (0.32-10 μm) were more likely to be affected by the sampling season.

Second, the aerosol samples, which were collected from a walkway in the downtown district of Hong Kong, were characterized with XPS. Six key elements were detected: N, S, Ca, Si, O and C. Carbon was also the dominant species on the surface. The chemical species concentrations were found to be highly size-dependent. The accumulation-mode particles (0.1-1.8 μm) were revealed to be covered with diverse organic chemical compositions and required further investigation.

Third, the traffic related aerosol samples were further examined by ToF-SIMS. The ToF-SIMS spectra of each size fraction were analyzed with principal component analysis (PCA) and the results showed that the particle surface compositions from the same mode exhibited similar surface features, but particles from different modes did not. Particles from stage 2, stage 6, and stage 10 were chosen to represent the coarse-mode, accumulation-mode, and nucleation-mode particles, respectively. They were examined using ToF-SIMS imaging and depth profiling. Particles of different modes showed distinct surface chemical compositions and near surface structures.

In summary, this study demonstrated the feasibility of applying XPS elemental composition analysis and chemical state determination, as well as ToF-SIMS depth profiling and imaging in understanding surface characteristics and the near surface structures of ambient aerosol particles.