Environmental Engineering Reference
In-Depth Information
laboratory experiments performed at branch levels when the maximum value
of the basal emission were reached (July-August). They were performed meet-
ing the requirements given by Niinemets et al. (
2011
). The basal emission from
different pools were determined by measuring the emission at 30 °C in the
presence and the absence of the PAR. For the other emitting species, an accu-
rate analysis of the basal emission values reported in the literature was made.
Values collected according to the experimental protocol described by Niinemets
et al. (
2011
) were selected when the basal emission reached the maximum value
(July-August). This critical analysis showed that, in many cases, the values of the
basal emissions used in our model were lower than those used in previous ones
(Steinbrecher et al.
2009
). Seasonality functions were developed in order to cor-
rect the basal emission values for seasonality, taking into due account the sprout-
ing and falling of leaves in Italian ecosystems located at different altitudes. The
emission (Ej) of each j
th
isoprenoid present in the grid cell was calculated using
the Eq.
3.1
:
n
n
E
O
MAX
T
+
L
nj
E
O
MAX
T
nj
×
ρ
nj
×
f
nj
×
c
T
nj
×
c
nj
×
c
nj
+
×
ρ
nj
×
f
nj
E
j
=
0
o
×
c
Tb
nj
×
c
nj
(3.1)
where n is the number of vegetation species emitting the j
th
isoprenoid,
E
O
max
T+L
nj
is the maximum seasonal value of basal emission from the T
+
L pool,
E
O
max
T
nj
is
the maximum seasonal value of the basal emission from the T pool,
ˁ
nj
is the bio-
mass density of the n emitting species,
f
nj
and
f
nj
c
Ta
nj
are correction factors account-
ing for the gradient of light and temperature within the canopy due to sun shading,
c
nj
and
c
Ta
nj
are the empirical coefficients of the Guenther algorithm for plants fol-
lowing a T
+
L emission mechanism (Guenther et al.
1995
),
c
Tb
nj
is the empirical
coefficient of the Guenther algorithm for plants emitting monoterpenes with a T
mechanism,
c
nj
is the correction term accounting for the seasonal variations of the
basal emissions.
In the model, different seasonality terms were adopted for deciduous and
evergreen vegetation species. Values of
ˁ
nj
in each grid cell were calculated by
multiplying weekly values of the LAI, obtained from high resolved satellite obser-
vations (MODIS) performed in 2006, for the values of SLA of each one of the
vegetation species present in the cell. SLA values were obtained by combining
data from the literature with laboratory experiments. Values of on leaf temperature
and incoming PAR radiation were collected from satellite observations and elabo-
rated by partners of CarboItaly. Figure
3.1
highlights the high spatial resolution
provided by the model, whereas Fig.
3.2
highlights its capability to provide isopre-
noid-specific emissions. Both figures were obtained by integrating data elaborated
on a 12 h basis. Such a distinction was important because many of the stronger
monoterpene emitters followed a T
+
L mechanism.
