Informatics analysis on inorganic compounds, surface imaging and depth profiling were carried out for PM2.5 using time-of-flight secondary ion mass spectrometry (TOF-SIMS) during different haze periods (autumn and winter). Both positive ions, such as NH4+, Si+, H+, Li+, Na+, Mg+, Al+, K+, Ca+, Ti+, Cr+, Fe+, Cu+, As+, Cs+ and Ba+, and negative ions, such as NO2-, NO3-, SO32-, SO42-, O-, Cl-, CN- and H-, were detected in the samples. Along with the increase of the depth, the signal intensity became weaker and weaker for most of the inorganic ions, however, it could be stronger for a few of them...
