A scanning proton microprobe (SPM) with high resolution and high sensitivity is applied to analyze single particles from steel industry in Shanghai. The elemental distribution and the variation of mean concentration of different elements with particle sizes were studied. The results indicated that the distributions of elements such as Fe

Cr and Mn are uniform

but K and Ca were rich on the surface of the particles. Moreover

the variation of mean concentration of different elements with particle sizes had regular features. Some harmful elements

such as Cu

Cr

Ni

Zn

Pb were contained in particles with size less than 5μm.