Epidemiological　studies　have　demonstrated　positive　relationships　between　increases　in　air　pollution　and　adverse　health　effects.　Physicochemical　characterization　and　toxicity　of　ambient　coarse　particles　(1.8-10　mu　m　diameter),　fine　particles　(1.8-10　mu　m　diameter)　and　ultrafine　particles　(＜0.1　mu　m　diameter)　collected　in　Shanghai　as　major　air　pollutants　were　investigated.　It　was　found　that　mass　concentrations　of　different　size　ambient　particles　in　Shanghai　urban　atmosphere　were　higher　than　those　in　suburban　atmosphere.　In　addition,　the　mass　concentrations　among　the　different　size　particles　were　different.　The　coarse　particles　consisted　of　minerals,　while　the　fine　particles　were　mainly　composed　of　soot　aggregates　and　sulfates;　ultrafine　particles　contained　only　small　amounts　of　particulates.　Crustal　elements　were　mainly　distributed　in　coarse　particles,　and　the　anthropogenic　elements　were　mainly　found　in　fine　particles.　Significant　amounts　of　calcium　and　magnesium　were　found　in　ultrafine　particles.　Fine　particles　were　found　to　generate　more　free　radical　than　coarse　and　ultrafine　particles.　Moreover,　the　results　of　the　cell　proliferation　assay　indicated　that　ultrafine　particles　were　more　cytotoxic　than　fine　and　coarse　particles.　Further　investigations　are　needed　to　study　the　mechanism　of　cytotoxic　induced　by　the　ambient　particles.　(C)　2010　Elsevier　Ltd.　All　rights　reserved.