Profile Measurements of BVOC Emissions from a Norway spruce

Abstract:

Biogenic volatile organic compounds (BVOCs) are known as a source of secondary organic aerosols (SOA) due to their high reactivity with O₃ and OH in the atmosphere [1, 2]. Norway spruce is one of the dominant boreal forest species in northern Europe, which has been considered to be high monoterpene (MT) emitters [3, 4]. BVOC emissions and compound composition vary considerably under different temperature and light conditions through growing season [5, 6]. Information of vertical profile emission patterns is indispensible for understanding chemical processes and oxidation sinks within canopy and for modelling evaluation.

We characterize the in-canopy BVOC emissions from a 120 years old Norway spruce in Central Sweden (Norunda, 60°05'N, 17°29'E). Air samples were taken during the growing season (June to September 2013 & 2014) from transparent dynamic branch chambers set up in a vertical profile with 4 levels (20 m, 15 m, 11 m and 3 m agl.) on the spruce. Samples were collected every hour from the chamber with Tenax-TA adsorbent tubes and a pocket pump, and analyzed later by gas chromatography and a mass selective detector (GC-MS) to quantify each trapped terpenoid compound. The emission spectrum of Norway spruce at 20 m canopy height was found to be more complex than the emissions spectra at lower canopy levels, and included isoprene, MT and SQT from June to September, while MT was the dominating terpenoid species. The emission spectra of July and August (isoprene, 14 MT and 3 SQT) were much more complex compared to June and September at the 20 m canopy level, and mainly caused by an increase of MT species during peak season. Similarly, isoprene showed a distinctive seasonal pattern, and was detected at all the heights during noon time except the bottom 3 m level during peak summer, but only at the highest layer (20 m) during noon in early or late summer. O₃ vertical profile data will be available for further chemical process analysis within canopy.

References

[1]M.Ehn et al., 2014, Nature, 506(7489), 476-479.

[2]M.Kulmala et al., 2004, Atmos. Environ., 4, 557-562.

[3]J.Rinne et al., 2005, Boreal Environ Res., 10, 425-436.

[4]J.Rinne et al., 2009, Boreal Environ Res., 14, 807-826.

[5]H.Hakola et al., 2006, Biogeosciences, 3(1), 93-101.

[6]N.Yassaa et al., 2012, Atmos. Chem. Phys., 12(15), 7215-7229.