On-site multi monitoring of isoprene and related compounds in forest air

Abstract

A novel analytical instrument has been developed for simple near-real time measurements of isoprene, and was applied to on-site analysis of forest air. Isoprene contained in sample air was trapped for 4 min and thermally desorbed to introduce it into a chemiluminescence cell. In this single column trapping/separation chemiluminescence (SCTS-CL) method, isoprene in ppbv level could be measured every 10 min with a limit of detection of 0.15 ppbv. In a plant chamber experiment, the isoprene concentration increased with light irradiation and decreased in the dark. The chamber experiment results by SCTS-CL agreed well with those obtained by thermal desorption-gas chromatography-mass spectrometry. In field analysis conducted in forest, isoprene concentration increased in the daytime and not found in the nighttime. On the other hand, α-pinene concentration was higher during the night compared to that in the day; probably because α-pinene emitted whole day and its decomposition was higher during the day. Other than isoprene, formaldehyde, ozone, nitrogen oxides, organic and inorganic acids were monitored simultaneously in the forest campaign, and daily variations and seasonal variations are discussed. Model of emission and decomposition was considered and daily variation of emission rates were simulated from changes in the concentrations of isoprene and α-pinene. The amplification of oxidants by BVOCs is discussed based on the field experimental results. © 2011 The Japan Society for Analytical Chemistry.