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Abstract
The large amount of volatile organic compound (VOC) emitted by vegetation modifies
air quality contributing to both tropospheric ozone and secondary organic aerosol
production. A better understanding of the factors controlling VOC emissions by vegetation
is mandatory in order to improve emission estimates derived from tropospheric chemistry
models. Although the Mediterranean shrublands are particularly abundant and rich in
emitting species, their emission potential is poorly known. Focusing on a VOC-emitting
shrub species widespread in the Mediterranean area (Cistus monspeliensis L.), we measured
and analysed its emissions of terpenes taking into account the age of individuals,
the season of sampling and the soil type. Sampling was done under natural environmental
conditions. Species of the genus Cistus are frequently reported to be storing species,
although we found only one stored monoterpene and three sesquiterpenes in very low
amount. Major emitted compounds were alpha-pinene and beta-myrcene. Total terpene
emissions were not influenced by plant age but emission of some individual terpenes
was positively correlated with age. A strong seasonal effect was evidenced. A larger
amount of terpenes was emitted during spring and summer than during fall and winter.
Summer emission rates were nearly 70 times higher than winter emission rates. Total
and individual terpene emissions were influenced by soil type; emissions on siliceous
substrate were ca. seven times higher than those on calcareous substrate. In conclusion,
it appears clearly that environmental factors such as soil nature and season should
be taken into account in order to achieve improved modelling of terpene emissions
by shrub species.