PM10 was collected at the urban and suburban sites of Zhengzhou city during autumn. High solution field emission scanning electron microscopy (FESEM) and image analysis (IA) were used to analyse the morphology and size distribution of individual particles in PM10. Plasmid DNA assay was employed to investigate the bioreactivity of PM10. The results showed that the coal fly ash particles were dominated in the PM10 at the urban site while mineral particles were dominated at the suburban site. The number-size distribution showed that the PM10 at the urban site was mainly concentrated in the range of 0.1 microm to 0.4 microm, but the PM10 at the suburban site was scattered in a relatively wider size range. The volume-size distribution demonstrated that the PM10 from both urban and suburban sites occurred mainly in the size range > 1 microm. These facts showed that by number the fine particles were prevailing in the PM10, while by volume (mass) the coarse particles had a major contribution to the total PM10. The results from plasmid assay showed that the bioreactivity of the urban PM10 was obviously higher than that of the suburban PM10.