Based　on　the　study　of　Beijing　PM10　bioreactivity　with　the　newly　developed　plasmid　DNA　assay　method,　and　analysis　for　trace　elements　of　PM10,　the　cause　of　plasmid　DNA　damage　by　PM10　was　investigated.　The　study　showed　that　plasmid　DNA　oxidative　damages　by　PM10　are　of　difference　in　different　seasons　at　various　areas.　The　concentrations　of　TM50　of　PM10　in　whole　samples　respectively　collected　at　urban　and　comparison　sites　during　winter　were　900　mu　g　mL(-1)　and　74　mu　g　mL(-1),　while　those　in　their　corresponding　soluble　fractions　were　540　mu　g　mL(-1)　and　86　mu　g　mL(-1).　In　contrast,　TM50　contents　of　PM10　from　summer　whole　samples　at　urban　areas　and　comparison　sites　were　116　mu　g　mL(-1)　and　210　mu　g　mL(-1),　whereas　those　in　their　soluble　fractions　were　180　mu　g　mL(-1)　and　306　mu　g　mL(-1).　The　difference　of　bioreactivity　of　Beijing　PM10　resulted　from　the　variation　of　trace　elements.　The　oxidative　damage　of　plasmid　DNA　caused　by　Pb,　Zn,　As　in　PM10　(whole　sample)　was　relatively　strong.　TM50　and　Mn,　V,　Zn　display　stronger　correlation　in　the　soluble　fraction.　It　implies　that　Zn　could　be　the　major　trace　element　in　Beijing　PM10　which　contributes　to　oxidative　damage　to　plasmid　DNA.