42
H.-J. Bolle
production respectively exchanges of carbon dioxide, nitrous oxides, dust, and
Biogene Volatile Organic Compounds (BVOCs). Worldwide it is estimated that the
biogene component of the VOCs exceeds with 127 - 480 Tg C yrl (Kesselmeier and
Staudt, 1999) the anthropogenic emission of non-met han hydrocarbones of 100 Tg
C yr- I (Singh and Zimmerman, 1992). There have been so far two major activities
in the Mediterranean area to determine fluxes between the vegetation and the
atmosphere, the MEDEFLU network (Miglietta and Peressotti, 1999) which
concentrated on CO 2 and the Biogenic Emissions in the Mediterranean Area
(BEMA) project which concentrated on BVOCs (Seufert et a1. 1997).
The Mediterranean area is rich of aromatic plants with high emission ofBVOCs
and the photochemical activity that transforms these compounds after they have been
released is high. Monoterpenes, which constitute one component of the BVOCs,
react with OH, N03, and 0 3, Depending on the NO/NOx ratio they either destroy or
produce ozone. (Lerdau 1991; Fehsenfeld et al. 1992; Meixner 1994). Due to these
reactions BVOCs, according to Seufert et a1. (1997), may increase - by depletion of
OH and producing CO - the lifetime of radiatively active gases such as methan,
foster the formation of aerosols and of cloud condensation nuclei, enhance the acid
deposition in remote areas by forming organic acids, and control the tropospheric
ozone formation. The assessment of the BVOC source strength up to now is limited
to few investigations of a limited number of species. More often investigated trees
are Quercus ilex and Pinus pinea, which have been identified as a major
monoterpene sources.
The carbon skeletons of terpenes are composed of characteristic C s units.
Isoprene belongs to the group with five carbon atoms. Monoterpenes consist of C IO
structures and are described in Kesselmeier and Staudt (1999). Kesselmeier et al.
(1996) list 18 Monoterpenes which are emitted by Quercus ilex of which the five
most frequent are a-Pinene, p-Pinene, Sabinene, 1,8 Cineole, and p-Cymene. Less
volatile terpenes consist of C 15 , C30, C4S or higher carbon structures. Other volatile
compounds are aldehydes and organic acids. Kesselmeier and Staudt list in total 37
volatile non-terpenoid compounds of which emission rates of different plants have
been estimated. The emission rates generally depend on the photosynthetic active
radiation (PAR), temperature, leaf position, plant age, season, and stress.
Consequently the individual measurements vary in wide limits. In the case of
Quercus ilex, as an example, at a PAR rate of 2000 f,Lmol photons m 2 Sl an emission
rate of acetic acid of only about 10 nmol m- 2 (projected leaf areayl was measured in
May while during a hot and dry while during a hot and dry day in August maximum
values were 30-40 nmol m- 2 (projected leaf areayl and negative values occurred at
eight o'clock in the morning. The respective numbers for formic acid are 20 nmol
m- 2 (projected leaf areayl in May and 50 nmol m- 2 (projected leaf area) I in August
(Gabriel et a1. 1999). Some data relevant for Mediterranean species are compiled in
Table 4a and 4b.
From data gained during a large field experiment in the natural reservation of
Castelporziano near Rome probably the first time it was attempted to estimate
BVOC emission fluxes for some major Mediterranean land cover types. The results
H.-J. Bolle
production respectively exchanges of carbon dioxide, nitrous oxides, dust, and
Biogene Volatile Organic Compounds (BVOCs). Worldwide it is estimated that the
biogene component of the VOCs exceeds with 127 - 480 Tg C yrl (Kesselmeier and
Staudt, 1999) the anthropogenic emission of non-met han hydrocarbones of 100 Tg
C yr- I (Singh and Zimmerman, 1992). There have been so far two major activities
in the Mediterranean area to determine fluxes between the vegetation and the
atmosphere, the MEDEFLU network (Miglietta and Peressotti, 1999) which
concentrated on CO 2 and the Biogenic Emissions in the Mediterranean Area
(BEMA) project which concentrated on BVOCs (Seufert et a1. 1997).
The Mediterranean area is rich of aromatic plants with high emission ofBVOCs
and the photochemical activity that transforms these compounds after they have been
released is high. Monoterpenes, which constitute one component of the BVOCs,
react with OH, N03, and 0 3, Depending on the NO/NOx ratio they either destroy or
produce ozone. (Lerdau 1991; Fehsenfeld et al. 1992; Meixner 1994). Due to these
reactions BVOCs, according to Seufert et a1. (1997), may increase - by depletion of
OH and producing CO - the lifetime of radiatively active gases such as methan,
foster the formation of aerosols and of cloud condensation nuclei, enhance the acid
deposition in remote areas by forming organic acids, and control the tropospheric
ozone formation. The assessment of the BVOC source strength up to now is limited
to few investigations of a limited number of species. More often investigated trees
are Quercus ilex and Pinus pinea, which have been identified as a major
monoterpene sources.
The carbon skeletons of terpenes are composed of characteristic C s units.
Isoprene belongs to the group with five carbon atoms. Monoterpenes consist of C IO
structures and are described in Kesselmeier and Staudt (1999). Kesselmeier et al.
(1996) list 18 Monoterpenes which are emitted by Quercus ilex of which the five
most frequent are a-Pinene, p-Pinene, Sabinene, 1,8 Cineole, and p-Cymene. Less
volatile terpenes consist of C 15 , C30, C4S or higher carbon structures. Other volatile
compounds are aldehydes and organic acids. Kesselmeier and Staudt list in total 37
volatile non-terpenoid compounds of which emission rates of different plants have
been estimated. The emission rates generally depend on the photosynthetic active
radiation (PAR), temperature, leaf position, plant age, season, and stress.
Consequently the individual measurements vary in wide limits. In the case of
Quercus ilex, as an example, at a PAR rate of 2000 f,Lmol photons m 2 Sl an emission
rate of acetic acid of only about 10 nmol m- 2 (projected leaf areayl was measured in
May while during a hot and dry while during a hot and dry day in August maximum
values were 30-40 nmol m- 2 (projected leaf areayl and negative values occurred at
eight o'clock in the morning. The respective numbers for formic acid are 20 nmol
m- 2 (projected leaf areayl in May and 50 nmol m- 2 (projected leaf area) I in August
(Gabriel et a1. 1999). Some data relevant for Mediterranean species are compiled in
Table 4a and 4b.
From data gained during a large field experiment in the natural reservation of
Castelporziano near Rome probably the first time it was attempted to estimate
BVOC emission fluxes for some major Mediterranean land cover types. The results