Gas exchange of BVOC

The chambers for measurement of forest floor BVOC were placed 10 to 30 m apart (Aaltonen et al., 2012). Stainless-steel collars (80 cm×40 cm×10 cm) for mounting the chambers on the soil had previously been installed at the site in September 2009 by pushing the collar edge through the moss and litter layers. The chambers (80 cm×40 cm×25 cm) are made of an aluminium frame with a transparent fluorinated ethylene 3min−1 in a 64-m long heated FEP tube propylene (FEP) film (0.05 mm) covering the sides and top from the inside. The chambers opened towards the north, leaving the south-facing side free of any barriers. When the chamber is open, it covered approximately 10 % of the collar area, allowing quite undisturbed litter input from trees. Two small fans continuously mix the air inside the chambers. The operation of the chambers is automated; each chamber is pneumatically closed for 15 min once every three hours, i.e. eight times per day, and the first 7 min non-steadystate part of the closures is used for quantifying the fluxes. Sample air is drawn from the chambers at a rate of 1.1 dm 3min−1 ) is taken from the main sample line and diverted into a PTR-MS (Ionicon Analytik, Innsbruck, Austria) with polytetrafluoroethylene (PTFE) tubing. Compressed ambient air, a mixture of air is drawn from six levels (4.2, 8.4, 16.8, 33.6, 50.4 and 67.2 m above ground) of measurements in mast located at the site with an internal diameter of 4 mm. A smaller air sample (flow 0.1 dm), is supplied into the chamber at the same flow rate as the sample air is drawn out to replace the sampled air volume in the chamber.

Aaltonen et al., 2012. Continuos VOC flux measurements on boreal forest floor. Plant Soil, DOI 10.1007/s11104-012-1553-4.