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Title:
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Methode ontwikkeling voor verbetering van de verificatie van niet-CO2 broeikasgasemissies
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Author(s):
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Published by:
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Publication date:
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ECN
Biomass, Coal and Environmental Research
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1-12-2004
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ECN report number:
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Document type:
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ECN-C--04-027
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ECN publication
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Number of pages:
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Full text:
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55
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Download PDF
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Abstract:
The main purpose of the project was the improvement of the accuracyof emission verification strategies for non-CO2 greenhouse gases on
the European and regional (countrywise) scale. Two Lagrangian type of
air pollution dispersion models have been adapted and were utilized
in order to arrive at accurate description of process fluxes at the
regional scale.
The most important improvements in the ECN COMET model were: better
and higher resolu-tion 3D trajectory data and a better parametrisation
of the mixing layer height. Furthermore measured vertical concentration
gradients measured at the tall tower at Cabauw (NL) were used compared
to the previous use of data for one measurement height only. The new
version of COMET produces a much better comparison between concentration
measurements and the model values, especially for the nighttime accumulation
values. The linear regression of hourly data for the whole year of 2002
of methane between observations and the model delivers a cor-relation
coefficient (r2) of 0.69. This means that the explained variation between
measurements and model values has improved with almost a factor of two.
From forward and inverse calculation we find that mixed layer averaged
concentrations of methane at Cabauw are mainly determined by sources
within The Netherlands. In the study pe-riod the contribution of The
Netherlands to the methane in air at Cabauw in excess to the back-ground
is 65-80%.
The total emission of the 6 areas of The Netherlands is estimated by
the model inversions with a rather stable emission rate of 70-80% of
the value of the estimate of the emission inventory METDAT, i.e. 1020
kton/yr for the base year 1995. The uncertainty analysis using a Monte
Carlo error simulation technique indicates a rather high uncertainty
of the individual emissions of the six separate emission areas in The
Netherlands. The uncertainty is higher for the whole 2002 year period
than for a shorter six week period in September/October 2002.
After updating the emissions with the optimised values as calculated
with the inverse COMET method, the correlation coefficient between observations
and model values does not improve significantly. The Root Mean Square
Error however is decreased substantially to about half the value obtained
when using the uncorrected emissions. Using the optimized emission field
also reduces the night-time overestimation of the modeled concentrations.
The present results do not allow to discern the spatial distribution
of the different source catego-ries over The Netherlands. This can be
attributed to several reasons like the error introduced by discretisation
of the source areas, numerical uncertainties in the (big) solution space
and the too high background concentrations used here (TM3, based on
1993 data).
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