In situ measurements of volatile organic compounds in a boreal forest

by H Hakola, H Hellen, M Hemmila, J Rinne, M Kulmala
ATMOSPHERIC CHEMISTRY AND PHYSICS ()
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Abstract

We present biogenic VOC, including sesquiterpenes, measurements at the\nSMEAR II station (Station For Measuring Forest Ecosystem-Atmosphere\nRelations) in Finland using an in situ gas chromatograph\nmass-spectrometer with 2 h time resolution. The measurements were\nconducted over the period October 2010-October 2011, at least one week\nevery month. To our knowledge there are no earlier species-speciated\nsemi-continuous BVOC data also covering dormant periods. This was also\nthe first time sesquiterpene mixing ratios were measured in a boreal\nforest.\nDuring the winter months, and still in March, the mixing ratios of all\nbiogenic compounds were very low, most of the time below detection\nlimits. The monoterpene mixing ratios increased in April and started to\nshow diurnal variability, with maximum mixing ratio at night and minima\nduring the day. The diurnal variability continued until October, after\nwhich the mixing ratios decreased and then only occasional episodes took\nplace. The diurnal variation was affected by boundary layer height.\nSesquiterpene mixing ratios were very low, only a few ppt. The main\nsesquiterpenes were longifolene and isolongifolene. The diurnal\nvariation of isoprene was opposite to the mono-and sesquiterpene diurnal\ncurve due to isoprene's light dependent emissions. Due to its daytime\nmaximum mixing ratios, isoprene also dominated hydroxyl radical\nreactivity in summer even though our isoprene measurements are\nunderestimates due to a breakthrough in a cold trap.

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