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| Titel |
Mercury vapor air–surface exchange measured by collocated micrometeorological and enclosure methods – Part I: Data comparability and method characteristics |
| VerfasserIn |
W. Zhu, J. Sommar, C.-J. Lin, X. Feng |
| 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 ; 15, no. 2 ; Nr. 15, no. 2 (2015-01-19), S.685-702 |
| Datensatznummer |
250119333
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| Publikation (Nr.) |
 copernicus.org/acp-15-685-2015.pdf |
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| Zusammenfassung |
Reliable quantification of air–biosphere exchange flux of elemental mercury
vapor (Hg0) is crucial for understanding the global biogeochemical cycle of
mercury. However, there has not been a standard analytical protocol for flux
quantification, and little attention has been devoted to characterize the
temporal variability and comparability of fluxes measured by different
methods. In this study, we deployed a collocated set of micrometeorological
(MM) and dynamic flux chamber (DFC) measurement systems to quantify
Hg0 flux over bare soil and low standing crop in an agricultural field.
The techniques include relaxed eddy accumulation (REA), modified Bowen ratio
(MBR), aerodynamic gradient (AGM) as well as dynamic flux chambers of
traditional (TDFC) and novel (NDFC) designs. The five systems and their
measured fluxes were cross-examined with respect to magnitude, temporal
trend and correlation with environmental variables.
Fluxes measured by the MM and DFC methods showed distinct temporal trends.
The former exhibited a highly dynamic temporal variability while the latter
had much more gradual temporal features. The diurnal characteristics reflected
the difference in the fundamental processes driving the measurements. The
correlations between NDFC and TDFC fluxes and between MBR and AGM fluxes
were significant (R>0.8, p<0.05), but the correlation
between DFC and MM fluxes were from weak to moderate (R=0.1–0.5).
Statistical analysis indicated that the median of turbulent fluxes estimated
by the three independent MM techniques were not significantly different.
Cumulative flux measured by TDFC is considerably lower (42% of AGM and
31% of MBR fluxes) while those measured by NDFC, AGM and MBR were similar
(<10% difference). This suggests that incorporating an
atmospheric turbulence property such as friction velocity for correcting the
DFC-measured flux effectively bridged the gap between the Hg0 fluxes
measured by enclosure and MM techniques. Cumulated flux measured by REA was
~60% higher than the gradient-based fluxes. Environmental
factors have different degrees of impacts on the fluxes observed by
different techniques, possibly caused by the underlying assumptions specific
to each individual method. Recommendations regarding the application of flux
quantification methods were made based on the data obtained in this study. |
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