Sesquiterpenes and oxygenated sesquiterpenes dominate the VOC (C<sub>5</sub>–C<sub>20</sub>) emissions of downy birches

Abstract. Biogenic volatile organic compounds (BVOCs) emitted by the forests are known to have strong impacts in atmosphere. However, lots of missing reactivity is found, especially forest air. Therefore better characterization sources and identification/quantification unknown reactive needed. While isoprene monoterpene (MT) emissions boreal needle trees been studied quite intensively, there much less knowledge on deciduous larger terpenes oxygenated (OVOCs). Here we quantified downy birch (Betula pubescens) leaf terpenes, green volatiles (GLVs) at SMEAR II site using situ gas chromatographs with mass spectrometers. Sesquiterpenes (SQTs) sesquiterpenes (OSQTs) were main compounds. Mean emission rates SQTs OSQTs significantly higher early growing season (510 650 ng gdw-1 h?1, respectively) compared (40 130 late (14 46 periods, indicating that growth a source these The had very clear diurnal variation afternoon maxima being average 4 8 times than seasonal means for OSQTs, respectively. ?-Caryophyllene ?-farnesene emitted. tentatively identified as 14-hydroxy-?-caryophyllene acetate (M=262 g mol?1) 6-hydroxy-?-caryophyllene (M=220 mol?1). Over whole season, total MT only 24 % 17 SQT OSQT emissions, A stressed tree pot was also studied, high ?-farnesene an unidentified detected together GLVs. Due relatively low volatility expected atmospheric chemistry, secondary aerosol (SOA) production.