Environmental Engineering Reference
In-Depth Information
a.s.l. between Forchetta Morrea, Prati S. Elia and Selva Piana, near the town of
Collelongo (Abruzzo, Italy, see Sect.
2.2.8
), at 95 km north-east from Rome.
Around the measuring site and at that elevation (1,500-1,700 m a.s.l.)
F. sylvat-
ica
is the dominant tree species for several hundred hectares. The BVOC sam-
pling site, located in a clearing (Prati S. Elia, 700 m wide and 1,500 m long) was
1,000 m a part from the CarboItaly tower in operation since 1993 to measure the
ecosystem exchange of water and CO
2
by Eddy Covariance. By considering the
complex shape of the area, the gradient method using tethered balloon profiles
was the preferred approach to measure VOC fluxes. Only with this approach was
indeed possible to collect samples above the average elevation of the canopy and
to get values representative of a large area. By collecting VOC at 4 levels from
30 to 200 m above the clearing, sufficient data were available in order to get reli-
able values of the fluxes. They were measured from July 29
th
to August 1
st
2008.
VOC were enriched into cartridges packed with Tenax TA adsorbent resin using
automated air sampling systems, equipped with temperature and pressure sensors
to maintain a constant flow of air. Vertical profiles of temperature, pressure and
relative humidity were also measured. After sampling, the cartridges were taken
to the laboratory and analyzed within 10 days by a Gas Chromatography Mass
Spectrometry (GC-MS) system equipped with a thermal desorption unit (Baraldi
et al.
1999
). Using the similarity approach, the Eq.
3.2
was used to calculate VOC
fluxes (Kuhn et al.
2007
):
C
Z
VOC
−
C
Z
VOC
−
U
·
K
VOC FLUX
=
(3.2)
Z
U
−
D
Z
L
−
D
−
Z
H
+
Z
L
LN
H
where Z
U
and Z
L
are the upper and lower levels (in m) where the VOC concentra-
tions are measured,
C
Z
VOC
and
C
Z
VOC
are the concentrations in µg m
−
3
measured
at the two levels; K is the Von Karman constant (0.4 in our case); d the average
height above canopy where gradient measurements starts;
Z
U
h
and
Z
h
are the
adiabatic correction function for heat under unstable conditions, that can be calcu-
lated according to Paulson (
1970
). An example of the vertical profiles collected at
the sampling site is shown in Fig.
3.4
. Clear gradients were measured for sabinene,
Fig. 3.4
Vertical profiles
of 08/01/08 solar time
08:45-09:45 am
