In situ measurements of volatile organic compounds in a boreal forest
1Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
2Department of Physical Sciences, University of Helsinki, P.O. Box 68, 00014 University of Helsinki, Finland
Abstract. We present biogenic VOC, including sesquiterpenes, measurements at the SMEAR II station (Station For Measuring Forest Ecosystem-Atmosphere Relations) in Finland using an in situ gas chromatograph mass-spectrometer with 2 h time resolution. The measurements were conducted over the period October 2010–October 2011, at least one week every month. To our knowledge there are no earlier species-speciated semi-continuous BVOC data also covering dormant periods.
During the winter months, and still in March, the concentrations of all biogenic compounds were very low, most of the time below detection limits. The monoterpene concentrations increased in April and started to show diurnal variability, with maximum concentrations at night and minima during the day. The diurnal variability continued until October, after which the concentrations decreased and then only occasional episodes took place. The diurnal variation was affected by boundary layer height. Sesquiterpene concentrations were very low, only a few ppt. The main sesquiterpenes were longifolene and isolongifolene. The diurnal variation of isoprene was opposite to the mono- and sesquiterpene diurnal curve due to isoprene's light dependent emissions. Due to its daytime maximum concentrations, isoprene also dominated hydroxyl radical reactivity in summer even though our isoprene measurements are underestimates due to a breakthrough in a cold trap.