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| Titel |
Evaluation of discrepancy between measured and modelled oxidized mercury species |
| VerfasserIn |
G. Kos, A. Ryzhkov, A. Dastoor, J. Narayan, A. Steffen, P. A. Ariya, L. Zhang |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 13, no. 9 ; Nr. 13, no. 9 (2013-05-14), S.4839-4863 |
| Datensatznummer |
250018644
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| Publikation (Nr.) |
 copernicus.org/acp-13-4839-2013.pdf |
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| Zusammenfassung |
| L. Zhang et al. (2012), in a recent report, compared model estimates with new
observations of oxidized and particulate mercury species (Hg2+ and
Hgp) in the Great Lakes region and found that the sum of Hg2+ and
Hgp varied between a factor of 2 to 10 between measurements and model.
They suggested too high emission inputs as Hg2+ and too fast oxidative
conversion of Hg0 to Hg2+ and Hgp as possible causes. This
study quantitatively explores measurement uncertainties in detail. These
include sampling efficiency, composition of sample, interfering species and
calibration errors. Model (Global/Regional Atmospheric Heavy Metals Model –
GRAHM) sensitivity experiments are used to examine the consistency between
various Hg measurements and speciation of Hg near emission sources to better
understand the discrepancies between modelled and measured concentrations of
Hg2+ and Hgp. We find that the ratio of Hg0, Hg2+ and
Hgp in the emission inventories, measurements of surface air
concentrations of oxidized Hg and measurements of wet deposition are
currently inconsistent with each other in the vicinity of emission sources.
Current speciation of Hg emissions suggests higher concentrations of
Hg2+ in air and in precipitation near emission sources; however,
measured air concentrations of Hg2+ and measured concentrations of Hg
in precipitation are not found to be significantly elevated near emission
sources compared to the remote regions. The averaged unbiased root mean
square error (RMSE) between simulated and observed concentrations of
Hg2+ is found to be reduced by 42% and for Hgp reduced by
40% for 21 North American sites investigated, when a ratio for
Hg0 : Hg2+ : Hgp in the emissions is changed from 50 : 40 : 10
(as specified in the original inventories) to 90 : 8 : 2. Unbiased RMSE reductions
near emissions sources in the eastern United States and Canada are found to
be reduced by up to 58% for Hg2+. Significant improvement in the
model simulated spatial distribution of wet deposition of mercury in North
America is noticed with the modified Hg emission speciation.
Measurement-related uncertainties leading to lower estimation of Hg2+
concentrations are 86%. Uncertainties yielding either to higher or lower
Hg2+ concentrations are found to be 36%. Finally, anthropogenic
emission uncertainties are 106% for Hg2+. Thus it appears that the
identified uncertainties for model estimates related to mercury speciation
near sources, uncertainties in measurement methodology and uncertainties in
emissions can close the gap between modelled and observed estimates of
oxidized mercury found in L. Zhang et al. (2012). Model sensitivity simulations
show that the measured concentrations of oxidized mercury, in general, are
too low to be consistent with measured wet deposition fluxes in North
America. Better emission inventories (with respect to speciation), better
techniques for measurements of oxidized species and knowledge of mercury
reduction reactions in different environments (including in-plume) in all
phases are needed for improving the mercury models. |
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