Emission of isoprene and carbonyl compounds from a boreal forest and wetland in Sweden

Abstract

Emission measurements of light hydrocarbons, light carbonyl compounds, and monoterpenes have been made with canister, DNPH, and Tenax samples, respectively, on Norway spruce (Picea abies), Scots pine (Pinus sylvestris), the floor of a mixed pine and spruce forest, and a Sphagnum fen at the NOPEX site (Northern hemisphere climate Processes and land-surface Experiment) in the southern boreal zone of Sweden, in 1995. The branch and ground measurements were made with the flow-through enclosure technique and static chamber technique, respectively. Norway spruce was found to emit significant amounts of isoprene, the normalised emission rate (30°C, 1000μmolm−2s−1) averaging 24±18nmolgdw−1h−1 (1.4μgCgdw−1h−1), and of carbonyls with normalised rates ranging from 10 to 150nmolgdw−1h−1 (0.3–4.6μgCgdw−1h−1). Acetone/acrolein and acetaldehyde dominated the carbonyl flux with 61 and 27%, respectively. The normalised monoterpene emission rate (30°C) varied from 17 to 60nmolgdw−1h−1 (2–7μgCgdw−1h−1), with α-pinene accounting for 34% of the flux. The emission from Scots pine included only traces of isoprene, while the emission rate of acetone/acrolein was comparable to that of the monoterpenes. The BVOC flux from the forest floor made up only a few percent of the total forest flux and included ethene and propane at several tens of nmolm−2h−1, and the monoterpenes at rates reaching 380nmolm−2h−1 (50μgCm−2h−1), dominated by α-pinene. A Sphagnum fen emitted isoprene at rates fully comparable to the areal flux of isoprene from the boreal spruce forest. Highest emission rates were observed from the low and wet micro-sites, as compared to the higher and drier hummocks. The average flux in June was 912±750nmolm−2h−1 (55±45μgCm−2h−1) and in August 6800±4000nmolm−2h−1 (408±240μgCm−2h−1). Monoterpene fluxes were 160±80nmolm−2h−1 (19±9μgCm−2h−1) in June and 760±480nmolm−2h−1 (90±60μgCm−2h−1) in August. Isoprene from Norway spruce and Sphagnum wetlands, as well as acetone/acrolein from Norway spruce and Scots pine, are shown here to be important components of the boreal emission of BVOC. More diurnal and seasonal data is needed to correctly evaluate the seasonal flux.