A variety of C<sub>1</sub>-C<sub>12</sub> carbonyl compounds were measured in the air of a boreal coniferous forest located in Hyytiälä, Southern Finland. 24-h samples were collected during March and April in 2003 using DNPH (2,4-dinitrophenyl hydrazine) coated C<sub>18</sub>-cartridges and analyzed by liquid chromatography-mass spectrometry (LC-MS). <br><br> Altogether 22 carbonyl compounds were quantified. The most abundant carbonyls were acetone (24-h average 1340 ng/m<sup>3</sup>), formaldehyde (480 ng/m<sup>3</sup>) and acetaldehyde (360 ng/m<sup>3</sup>). In contrast, scaling of concentrations against reactivity with the hydroxyl (OH) radical significantly increased the contribution of larger aldehydes and ketones (e.g. decanal, octanal and 6-methyl-5-hepten-2-one). Concentrations of monoterpene reaction products nopinone (9 ng/m<sup>3</sup>) and limona ketone (5 ng/m<sup>3</sup>) were low compared to the most abundant low molecular weight carbonyls. The total concentration of carbonyl compounds in Hyytiälä in April/March 2003 was much higher than the concentration of aromatic hydrocarbons and monoterpenes in April 2002. <br><br> Lifetimes of the measured carbonyls with respect to reactions with OH radicals, ozone (O<sub>3</sub>), and nitrate (NO<sub>3</sub>) radicals as well as photolysis were estimated. The main sinks for most of the carbonyl compounds in Hyytiälä in springtime are expected to be reactions with the OH radical and photolysis. For 6-methyl-5-hepten-2-one and limona ketone also reactions with ozone are important. The sources of carbonyl compounds are presently highly uncertain. Due to the relatively short lifetimes of aldehydes and ketones, secondary biogenic and anthropogenic sources, that is oxidation of volatile organic compounds, and primary biogenic sources are expected to dominate in Hyytiälä.