Verlag des Forschungszentrums Jülich
JUEL-3465
This analytical method has been applied for measurements of the VOC emissions from
crop species with a mobile plant encosure system and for the automated measurement
of ambient VOC concentrations in a rural environment. The results show that the
emission of hydrocarbons from maize (zea mais) has been overestimated in the past.
However, the results of earlier measurements indicating low VOC-emissions from
other crop species are confirmed by this work. From this work and an extensive
literature review an upper limit for the emission of monoterpenes from cereals,
sugar beets (beta vulgaris), potatoes (solanum tuberosum), and clover
(trifolium ssp.) of about 10 ng/g(dry weight)/h per compound can be derived. As
a consequence, the contribution of croplands to the hydrocarbon emissions over
Europe is smaller than 1% and negligible compared to other biogenic and
anthropogenic sources.
The emission rates of oxigenated compounds usually were in the same range as the
hydrocarbon emissions with upper limits for the emission of alkanals between
0.1 and 1 µg/gh. However, strong emissions of Z-3-Hexen-1-ol and
Z-3-Hexenyl-1-acetate from sugar beets (together 3.5 µg/gh) and from
grassland (up to 1.2 %g/gh) have been observed. The high variability most
probably arises from stress reactions. The results indicate a high sensitivity
of sugar beets towards physical stress. Other crops did not show a measurable
reaction to mechanical stress.
Furthermore, strong monoterpene emissions from sunflowers (helianthus annus)
have been measured. With day-time emissions of 10 - 30 µg/gh these plants are
the strongest terpene emitters among the investigated crop species. Comparable
monoterpene emissions are only reported for tomatoes (lycopersicon lycopersicum)
and pistachios (pistacia vera). VOC emissions in this order of magnitude
can have a strong influence on the local photochemistry. Models which describe
VOC-emissions only as a result of evaporation from pools or of their biosynthesis
can not explain the observed temperature and light dependence of the terpene
emissions from sunflowers. With a new emission algorythm, however, which considers
both pathways the major features of the diurnal variation can be described.
The mechanisms that led to strong emissions of sesquiterpenes at night are not
yet understood.
Thus the results of the measurements performed in this work together with other
recent experimental results and model calculations indicate that the contribution
of croplands to the photochemical formation of ozone over Europe is comparitively
small. The emission of light alcohols and ketones from croplands however requires
further research.
Wedel, Arno
Bedeutung flüchtiger organischer Verbindungen aus landwirtschaftlich genutzten Pflanzen für die Chemie der Atmosphäre
213 S., 1997
In this work a new method for the qualitative and quantitative analysis of volatile
organic compounds (C5-C15) has been developed. The limit of
detection is as low as 20 pg/l for many substances (corresponding to mixing ratios
in the lower pptv-range) and that the response is linear up to concentrations of
0.1 µg/l (corresponding to mixing ratios of some 10 ppbv). The interference
from water vapor is negligible, the interference from ozone is reduced substantially
by adding NO to the sample. It is shown that this method is suitable for the
measurement terpenes and oxigenated VOC.
Ambient air measurements were conducted during the POPCORN campaign in a sparcely
populated rural environment in North-Eastern Germany. During this field campaign
biogenic VOC contributed about 7% to the total atmospheric VOC content of
about 13 ppbC. Owing to their higher reactivity their contribution to the local
photooxidant formation was around 50%. However, the contribution of compounds
that were identified as emissions from local crops was less than 10% of the
total VOC turnover.
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