In situ measurements of volatile organic compounds in a boreal forest

H Hakola,J Rinne,M Kulmala,M Hemmilä,H Hellén

doi:10.5194/acp-12-11665-2012

Abstract

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. This was also the first time sesquiterpene mixing ratios were measured in a boreal forest. During the winter months, and still in March, the mixing 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 variability, with maximum mixing ratio at night and minima during the day. The diurnal variability continued until October, after which the mixing ratios decreased and then only occasional episodes took place. The diurnal variation was affected by boundary layer height. Sesquiterpene mixing ratios 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 mixing ratios, isoprene also dominated hydroxyl radical reactivity in summer even though our isoprene measurements are underestimates due to a breakthrough in a cold trap.

Highlights

Volatile organic compounds (VOCs), especially isoprene and monoterpenes, and some sesquiterpenes, are emitted in large amounts from a boreal forest (Tarvainen et al, 2007; Rinne et al, 2009)
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
In the atmosphere they react rapidly with the hydroxyl radical, the nitrate radical and ozone, participating in the complex atmospheric chemical processes forming ozone (Sillman, 1999; Kleinmann, 2005). They are involved in new particle formation and growth processes (Kulmala et al, 2004a; Tunved et al, 2006; Bonn et al, 2008)

Summary

Introduction

Volatile organic compounds (VOCs), especially isoprene and monoterpenes, and some sesquiterpenes, are emitted in large amounts from a boreal forest (Tarvainen et al, 2007; Rinne et al, 2009) In the atmosphere they react rapidly with the hydroxyl radical, the nitrate radical and ozone, participating in the complex atmospheric chemical processes forming ozone (Sillman, 1999; Kleinmann, 2005). They are involved in new particle formation and growth processes (Kulmala et al, 2004a; Tunved et al, 2006; Bonn et al, 2008). Compound identification in PTR-MS measurements is less certain than with GC-MS, and PTR-MS cannot separate compounds with the same mass, e.g., monoterpenes, from each other

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Conclusion