Use of a global model to understand speciated atmospheric mercury observations at five high-elevation sites
Atmospheric mercury (Hg) measurements using the Tekran<sup>®</sup> analytical system from five high-elevation sites (1400–3200 m elevation), one in Asia and four in the western US, were compiled over multiple seasons and years, and these data were compared with the GEOS-Chem global model...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2015-02-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/15/1161/2015/acp-15-1161-2015.pdf |
| _version_ | 1818887512500731904 |
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| author | P. Weiss-Penzias H. M. Amos N. E. Selin M. S. Gustin D. A. Jaffe D. Obrist G.-R. Sheu A. Giang |
| author_facet | P. Weiss-Penzias H. M. Amos N. E. Selin M. S. Gustin D. A. Jaffe D. Obrist G.-R. Sheu A. Giang |
| author_sort | P. Weiss-Penzias |
| collection | DOAJ |
| description | Atmospheric mercury (Hg) measurements using the
Tekran<sup>®</sup> analytical system from five
high-elevation sites (1400–3200 m elevation), one in Asia and four in the
western US, were compiled over multiple seasons and years, and these data
were compared with the GEOS-Chem global model. Mercury data consisted of
gaseous elemental Hg (GEM) and "reactive Hg" (RM), which is a combination
of the gaseous oxidized (GOM) and particulate bound
(< 2.5 μm) (PBM) fractions as measured by the
Tekran<sup>®</sup> system. We used a subset of the
observations by defining a "free tropospheric" (FT) data set by screening
using measured water vapor mixing ratios. The oxidation scheme used by the
GEOS-Chem model was varied between the standard run with Br oxidation and an
alternative run with OH–O<sub>3</sub> oxidation. We used this model–measurement
comparison to help interpret the spatio-temporal trends in, and relationships
among, the Hg species and ancillary parameters, to understand better the
sources and fate of atmospheric RM. The most salient feature of the data
across sites, seen more in summer relative to spring, was that RM was
negatively correlated with GEM and water vapor mixing ratios (WV) and
positively correlated with ozone (O<sub>3</sub>), both in the standard model and
the observations, indicating that RM was formed in dry upper altitude air
from the photo-oxidation of GEM. During a free tropospheric transport high RM
event observed sequentially at three sites from Oregon to Nevada, the slope
of the RM / GEM relationship at the westernmost site was
−1020 ± 209 pg ng<sup>−1</sup>, indicating near-quantitative GEM-to-RM
photochemical conversion. An improved correlation between the observations
and the model was seen when the model was run with the OH–O<sub>3</sub> oxidation
scheme instead of the Br oxidation scheme. This simulation produced higher
concentrations of RM and lower concentrations of GEM, especially at the
desert sites in northwestern Nevada. This suggests that future work should
investigate the effect of Br- and O<sub>3</sub>-initiated gas-phase oxidation
occurring simultaneously in the atmosphere, as well as aqueous and
heterogeneous reactions to understand whether there are multiple global
oxidants for GEM and hence multiple forms of RM in the atmosphere. If the
chemical forms of RM were known, then the collection efficiency of the
analytical method could be evaluated better. |
| first_indexed | 2024-12-19T16:38:25Z |
| format | Article |
| id | doaj.art-2bb44583730b46b5a272833a9b33f852 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-19T16:38:25Z |
| publishDate | 2015-02-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-2bb44583730b46b5a272833a9b33f8522022-12-21T20:13:54ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242015-02-011531161117310.5194/acp-15-1161-2015Use of a global model to understand speciated atmospheric mercury observations at five high-elevation sitesP. Weiss-Penzias0H. M. Amos1N. E. Selin2M. S. Gustin3D. A. Jaffe4D. Obrist5G.-R. Sheu6A. Giang7Microbiology and Environmental Toxicology, University of California, Santa Cruz, USASchool of Public Health, Harvard University, Cambridge, Massachusetts, USADepartment of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Massachusetts, USADepartment of Natural Resources and Environmental Science, University of Nevada, Reno, USASchool of STEM Physical Sciences Division, University of Washington, Bothell, USADivision of Atmospheric Sciences, Desert Research Institute, Reno, Nevada, USADepartment of Atmospheric Science, National Central University, Taoyuan City, TaiwanDepartment of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Massachusetts, USAAtmospheric mercury (Hg) measurements using the Tekran<sup>®</sup> analytical system from five high-elevation sites (1400–3200 m elevation), one in Asia and four in the western US, were compiled over multiple seasons and years, and these data were compared with the GEOS-Chem global model. Mercury data consisted of gaseous elemental Hg (GEM) and "reactive Hg" (RM), which is a combination of the gaseous oxidized (GOM) and particulate bound (< 2.5 μm) (PBM) fractions as measured by the Tekran<sup>®</sup> system. We used a subset of the observations by defining a "free tropospheric" (FT) data set by screening using measured water vapor mixing ratios. The oxidation scheme used by the GEOS-Chem model was varied between the standard run with Br oxidation and an alternative run with OH–O<sub>3</sub> oxidation. We used this model–measurement comparison to help interpret the spatio-temporal trends in, and relationships among, the Hg species and ancillary parameters, to understand better the sources and fate of atmospheric RM. The most salient feature of the data across sites, seen more in summer relative to spring, was that RM was negatively correlated with GEM and water vapor mixing ratios (WV) and positively correlated with ozone (O<sub>3</sub>), both in the standard model and the observations, indicating that RM was formed in dry upper altitude air from the photo-oxidation of GEM. During a free tropospheric transport high RM event observed sequentially at three sites from Oregon to Nevada, the slope of the RM / GEM relationship at the westernmost site was −1020 ± 209 pg ng<sup>−1</sup>, indicating near-quantitative GEM-to-RM photochemical conversion. An improved correlation between the observations and the model was seen when the model was run with the OH–O<sub>3</sub> oxidation scheme instead of the Br oxidation scheme. This simulation produced higher concentrations of RM and lower concentrations of GEM, especially at the desert sites in northwestern Nevada. This suggests that future work should investigate the effect of Br- and O<sub>3</sub>-initiated gas-phase oxidation occurring simultaneously in the atmosphere, as well as aqueous and heterogeneous reactions to understand whether there are multiple global oxidants for GEM and hence multiple forms of RM in the atmosphere. If the chemical forms of RM were known, then the collection efficiency of the analytical method could be evaluated better.http://www.atmos-chem-phys.net/15/1161/2015/acp-15-1161-2015.pdf |
| spellingShingle | P. Weiss-Penzias H. M. Amos N. E. Selin M. S. Gustin D. A. Jaffe D. Obrist G.-R. Sheu A. Giang Use of a global model to understand speciated atmospheric mercury observations at five high-elevation sites Atmospheric Chemistry and Physics |
| title | Use of a global model to understand speciated atmospheric mercury observations at five high-elevation sites |
| title_full | Use of a global model to understand speciated atmospheric mercury observations at five high-elevation sites |
| title_fullStr | Use of a global model to understand speciated atmospheric mercury observations at five high-elevation sites |
| title_full_unstemmed | Use of a global model to understand speciated atmospheric mercury observations at five high-elevation sites |
| title_short | Use of a global model to understand speciated atmospheric mercury observations at five high-elevation sites |
| title_sort | use of a global model to understand speciated atmospheric mercury observations at five high elevation sites |
| url | http://www.atmos-chem-phys.net/15/1161/2015/acp-15-1161-2015.pdf |
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