Air ionization has been used for electro-static control of the semi-conductor industries. The conventional-type ionizers have the defect : creating small particles from the discharge emitters. There are two sources of the particle generation. One is eroded surfaces of emitters and the other is deposits on the emitters. We have analyzed the erosion and contamination of air ionizer emitters with various characterization technologies : Corona Discharge Spectroscopy, Atomospheric Pressure Ionization Mass Spectrometer (APIMS), Auger Electron Spectroscopy (AES), Electron Probe Microanalysis (EPMA), Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Diffractmetry (XRD). The particle generation from metallic emitters themselves is induced by oxidation of emitter surfaces due to corona discharge. Deposits on the emitters consist of the following materials : oxidized metallic compounds, SiO2 material formed from ultra-fine aerosol particles penetrating through ULPA filters, inorganic compounds of carbonate and nitrate synthesized from ambient air, and organic compounds of carboxylic acid or ammonium oxalate synthesized from organic solvent vapor.