The　levels　of　carbonyl　compounds　in　Shanghai　ambient　air　were　measured　in　five　periods　from　January　2007　to　October　2007　(covering　winter,　high-air-pollution　days,　spring,　summer　and　autumn).　A　total　of　114　samples　were　collected　and　eighteen　carbonyls　were　identified.　Formaldehyde,　acetaldehyde　and　acetone　were　the　most　abundant　carbonyls　and　their　mean　concentrations　of　19.40　+/-　12.00,　15.92　+/-　12.07　and　11.86　+/-　7.04　mu　g　m(-3)　respectively,　in　the　daytime　for　five　sampling　periods.　Formaldehyde　and　acetaldehyde　showed　similar　diurnal　profiles　with　peak　mixing　ratios　in　the　morning　and　early　afternoon　during　the　daytime.　Their　mean　concentrations　were　highest　in　summer　and　lowest　in　winter.　Acetone　showed　reversed　seasonal　variation.　The　high　molecular　weight　(HMW,　a　parts　per　thousand　yenC5)　carbonyls　also　showed　obvious　diurnal　variations　with　higher　concentrations　in　the　daytime　in　summer　and　autumn,　while　they　were　all　not　detected　in　winter.　Formaldehyde　and　acetaldehyde　played　an　important　role　in　removing　OH　radicals　in　the　atmosphere,　but　the　contribution　of　acetone　was　below　1%.　The　carbonyls　levels　in　high-air-pollution　days　were　reported.　More　carbonyl　species　with　higher　concentrations　were　found　in　high-air-pollution　days　than　in　spring.　These　carbonyls　were　transported　with　other　pollutants　from　north　and　northwest　in　March　27　to　April　2,　2007　and　then　mixed　with　local　sources.　Comparing　with　Beijing　and　Guangzhou,　the　concentrations　of　formaldehyde　and　acetaldehyde　in　Shanghai　were　the　highest,　which　indicated　that　the　air　pollution　in　Shanghai　was　even　worse　than　expected.