Fine　particulate　matter　with　aerodynamic　diameter　less　than　2.5　mu　m　(PM2.5)　Was　collected　at　urban　and　suburban　sites　in　Shanghai　from　April　2005　to　March　2006.　Average　mass　concentrations　of　PM2.5　ranged　from　43.5　to　149　mu　g　m(-3)　in　the　urban　area　and　21.7　to　159　mu　g　m(-3)　in　suburban　area.　The　mass　levels　of　PM2.5　sampled　at　urban　and　suburban　sites　showed　seasonal　variation　with　much　higher　values　in　winter　and　spring,　lower　values　in　summer,　and　the　lowest　in　autumn.　The　results　of　environmental　scanning　electron　microscopy　(ESEM)　showed　that　Shanghai　PM2.5　was　consisted　of　soot　aggregates,　coal　fly　ashes,　minerals,　bio-particles　and　unidentified　particles.　Inductively　coupled　plasma　atomic　mission　spectrum　(ICP-AES)　results　showed　total　elements　in　Shanghai　PM2.5　increased　gradually　from　summer　to　winter　and　remained　at　a　relatively　high　level　in　spring.　There　was　a　significant　difference　in　the　mass　of　elements　in　PM2.5　collected　in　urban　and　in　suburban　atmosphere.　Enrichment　factor　(EF)　analysis　results　demonstrated　that　K,　Na,　Ca,　Mg,　Al,　Fe,　Ba　and　Sr　originated　from　natural　sources,　while　As,　Cu,　Zn,　Ph,　Cd,　Mn,　Ni　and　Se　were　emitted　from　anthropogenic　sources.　The　plasmid　DNA　assay　showed　that　potential　toxicity　of　Shanghai　PM2.5　collected　at　urban　and　suburban　sampling　sites,　and　in　different　seasons,　varied　greatly.　Toxicity　of　the　Shanghai　urban　winter　PM2.5　sample　was　much　stronger　compared　to　any　of　the　other　samples.　Heavy　metals　in　Shanghai　PM2.5,　including　Cu,　Zn,　Ph,　Cd,　Cr,　Mn,　and　Ni,　might　have　synergic-effects　on　plasmid　DNA　damage.　(c)　2008　Elsevier　Ltd.　All　rights　reserved.