Carbonyl compounds in boreal coniferous forest air in Hyytiälä, Southern Finland

[摘要] A variety of C₁-C₁₂ carbonyl compounds were measured in the air ofa boreal coniferous forest located in Hyytiälä, Southern Finland.24-hour samples were collected during March and April in 2003 using DNPH(2,4-dinitrophenyl hydrazine) coated C₁₈-cartridges and analyzed byliquid chromatography-mass spectrometry (LC-MS).Altogether 22 carbonyl compounds were quantified. The most abundantcarbonyls were acetone (24-hour average 1340ng/m³), formaldehyde(480ng/m³) and acetaldehyde (360ng/m³). Concentrations of monoterpenereaction products nopinone (9ng/m³) and limona ketone (5ng/m³)were low compared to the most abundant low molecular weight carbonyls.Trajectory analysis showed that highest concentrations of carbonyls weremeasured in the air masses coming from the East and the lowest in the airmasses cycled long time over Scandinavia. The total concentration ofcarbonyl compounds in Hyytiälä in March/April 2003 was much higherthan the concentration of aromatic hydrocarbons and monoterpenes in April2002.Scaling the concentrations against reactivity with the OH-radical showed,that in spite of relatively low ambient concentrations higher molecularweight aldehydes contribute significantly to the total OH-reactive mass ofcarbonyls. The impact of carbonyl compounds on OH-radical chemistry isimportant. Contribution of carbonyls as an OH sink is comparable to that ofNO₂ and higher than monoterpenes and aromatic hydrocarbons.Lifetimes of the measured carbonyls with respect to reactions with OHradicals, ozone (O₃), and nitrate (NO₃) radicals as well asphotolysis were estimated. The main sink reactions for most of the carbonylcompounds in Hyytiälä in springtime are expected to be reactionswith the OH radical and photolysis. For 6-methyl-5-hepten-2-one and limonaketone also reactions with ozone are important. The sources of carbonylcompounds are presently highly uncertain. Based on the comparisons withurban concentrations the direct anthropogenic emissions are not as importantas secondary biogenic and anthropogenic sources or primary biogenic sourcesin Hyytiälä.

[学科分类] 大气科学