Isoprene and monoterpene measurements in a secondary forest in northern Benin

[摘要] The biogenic volatile organic compound (BVOC) composition of ambient air ata rural field site near Djougou, Benin has been studied as part of the AMMA(African Monsoon Multidisciplinary Analysis) project. Ambient air wassampled during day and night during the period 2 June 2006 to 13 June 2006.Gas samples from within the forest canopy and from branch and cuvetteenclosure systems for four vegetation species were also obtained andemissions flux estimates made. All samples were analysed for the presence ofisoprene, monoterpenes and sesquiterpenes by either gas chromatography-timeof flight mass spectrometry (GC-TOF/MS) or comprehensive gaschromatography-time of flight mass spectrometry (GCxGC-TOF/MS).Concentrations of isoprene ranged from a few tens of pptV to in excess of3000 pptV. Similar concentration ranges for certain monoterpenes were alsoobserved. Limonene was seen at a maximum concentration in ambient air of5000 pptV. The combination of leaf-level observations and direct analysis ofdried vegetation samples suggests that emissions of terpene species fromindigenous species are unlikely to account for the unexpectedly high ambientconcentrations of monoterpenes. Leaf scale emission measurements andbiological sample analysis indicated that \textit{Anacardium occidentale}, a non-native crop species foundthroughout the tropics, was the dominant source of monoterpenes at thislocation. These preliminary findings suggest that activities involvingspecies replacement have potential implications for the chemistry of theAfrican troposphere that have not been widely considered previously.

[学科分类] 大气科学