Atmos. Chem. Phys. Atmospheric Chemistry and Physics, vol. 12 (2012) pp. 11665-11678
We present biogenic VOC, including sesquiter-penes, measurements at the SMEAR II station (Station For Measuring Forest Ecosystem-Atmosphere Relations) in Fin-land 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. This was also the first time sesquiterpene mixing ratios were measured in a boreal forest. During the winter months, and still in March, the mix-ing ratios of all biogenic compounds were very low, most of the time below detection limits. The monoterpene mixing ratios increased in April and started to show diurnal variabil-ity, with maximum mixing ratio at night and minima dur-ing the day. The diurnal variability continued until October, after which the mixing ratios decreased and then only oc-casional episodes took place. The diurnal variation was af-fected by boundary layer height. Sesquiterpene mixing ra-tios 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 diur-nal curve due to isoprene's light dependent emissions. Due to its daytime maximum mixing ratios, isoprene also domi-nated hydroxyl radical reactivity in summer even though our isoprene measurements are underestimates due to a break-through in a cold trap.
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