Simulation of radon-222 with the GEOS-Chem global model: emissions, seasonality, and convective transport
<p>Radon-222 (<span class="inline-formula"><sup>222</sup></span>Rn) is a short-lived radioactive gas naturally emitted from land surfaces and has long been used to assess convective transport in atmospheric models. In this study, we simulate <span class=&qu...
| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2021-02-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/1861/2021/acp-21-1861-2021.pdf |
| _version_ | 1819060997340528640 |
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| author | B. Zhang H. Liu J. H. Crawford G. Chen T. D. Fairlie S. Chambers C.-H. Kang A. G. Williams K. Zhang D. B. Considine M. P. Sulprizio R. M. Yantosca |
| author_facet | B. Zhang H. Liu J. H. Crawford G. Chen T. D. Fairlie S. Chambers C.-H. Kang A. G. Williams K. Zhang D. B. Considine M. P. Sulprizio R. M. Yantosca |
| author_sort | B. Zhang |
| collection | DOAJ |
| description | <p>Radon-222 (<span class="inline-formula"><sup>222</sup></span>Rn) is a short-lived radioactive gas
naturally emitted from land surfaces and has long been used to assess
convective transport in atmospheric models. In this study, we simulate
<span class="inline-formula"><sup>222</sup></span>Rn using the GEOS-Chem chemical transport model to improve our
understanding of <span class="inline-formula"><sup>222</sup></span>Rn emissions and surface concentration seasonality
and characterize convective transport associated with two Goddard Earth
Observing System (GEOS) meteorological products, the Modern-Era Retrospective
analysis for Research and Applications (MERRA) and GEOS Forward Processing (GEOS-FP). We
evaluate four global <span class="inline-formula"><sup>222</sup></span>Rn emission scenarios by comparing model
results with observations at 51 surface sites. The default emission scenario
in GEOS-Chem yields a moderate agreement with surface observations globally
(68.9 % of data within a factor of 2) and a large underestimate of winter
surface <span class="inline-formula"><sup>222</sup></span>Rn concentrations at Northern Hemisphere midlatitudes and
high latitudes due to an oversimplified formulation of <span class="inline-formula"><sup>222</sup></span>Rn emission
fluxes (1 atom cm<span class="inline-formula"><sup>−2</sup></span> s<span class="inline-formula"><sup>−1</sup></span> over land with a reduction by a factor of 3 under
freezing conditions). We compose a new global <span class="inline-formula"><sup>222</sup></span>Rn emission scenario
based on Zhang et al. (2011) and demonstrate its potential to improve
simulated surface <span class="inline-formula"><sup>222</sup></span>Rn concentrations and seasonality. The regional
components of this scenario include spatially and temporally varying
emission fluxes derived from previous measurements of soil radium content
and soil exhalation models, which are key factors in determining <span class="inline-formula"><sup>222</sup></span>Rn
emission flux rates. However, large model underestimates of surface
<span class="inline-formula"><sup>222</sup></span>Rn concentrations still exist in Asia, suggesting unusually high
regional <span class="inline-formula"><sup>222</sup></span>Rn emissions. We therefore propose a conservative
upscaling factor of 1.2 for <span class="inline-formula"><sup>222</sup></span>Rn emission fluxes in China, which was
also constrained by observed deposition fluxes of <span class="inline-formula"><sup>210</sup></span>Pb (a progeny of
<span class="inline-formula"><sup>222</sup></span>Rn). With this modification, the model shows better agreement with
observations in Europe and North America (<span class="inline-formula">></span> 80 % of data within
a factor of 2) and reasonable agreement in Asia (close to 70 %). Further
constraints on <span class="inline-formula"><sup>222</sup></span>Rn emissions would require additional concentration
and emission flux observations in the central United States, Canada, Africa, and
Asia. We also compare and assess convective transport in model simulations
driven by MERRA and GEOS-FP using observed <span class="inline-formula"><sup>222</sup></span>Rn vertical profiles in
northern midlatitude summer and from three short-term airborne campaigns.
While simulations with both GEOS products are able to capture the observed
vertical gradient of <span class="inline-formula"><sup>222</sup></span>Rn concentrations in the lower troposphere (0–4 km), neither correctly represents the level of convective detrainment,
resulting in biases in the middle and upper troposphere. Compared with
GEOS-FP, MERRA leads to stronger convective transport of <span class="inline-formula"><sup>222</sup></span>Rn, which
is partially compensated for by its weaker large-scale vertical advection,
resulting in similar global vertical distributions of <span class="inline-formula"><sup>222</sup></span>Rn
concentrations between the two simulations. This has important<span id="page1862"/> implications
for using chemical transport models to interpret the transport of other
trace species when these GEOS products are used as driving meteorology.</p> |
| first_indexed | 2024-12-21T14:35:53Z |
| format | Article |
| id | doaj.art-fe3098c00e6a4859b6d913df8b463a76 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-21T14:35:53Z |
| publishDate | 2021-02-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-fe3098c00e6a4859b6d913df8b463a762022-12-21T19:00:20ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242021-02-01211861188710.5194/acp-21-1861-2021Simulation of radon-222 with the GEOS-Chem global model: emissions, seasonality, and convective transportB. Zhang0H. Liu1J. H. Crawford2G. Chen3T. D. Fairlie4S. Chambers5C.-H. Kang6A. G. Williams7K. Zhang8D. B. Considine9M. P. Sulprizio10R. M. Yantosca11National Institute of Aerospace, Hampton, Virginia, USANational Institute of Aerospace, Hampton, Virginia, USANASA Langley Research Center, Hampton, Virginia, USANASA Langley Research Center, Hampton, Virginia, USANASA Langley Research Center, Hampton, Virginia, USAAustralian Nuclear Science and Technology Organization, Kirrawee, New South Wales, AustraliaDepartment of Chemistry, Jeju National University, Jeju, Republic of KoreaAustralian Nuclear Science and Technology Organization, Kirrawee, New South Wales, AustraliaPacific Northwest National Laboratory, Richland, Washington, USANASA Headquarters, Washington D.C., USAJohn A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USAJohn A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA<p>Radon-222 (<span class="inline-formula"><sup>222</sup></span>Rn) is a short-lived radioactive gas naturally emitted from land surfaces and has long been used to assess convective transport in atmospheric models. In this study, we simulate <span class="inline-formula"><sup>222</sup></span>Rn using the GEOS-Chem chemical transport model to improve our understanding of <span class="inline-formula"><sup>222</sup></span>Rn emissions and surface concentration seasonality and characterize convective transport associated with two Goddard Earth Observing System (GEOS) meteorological products, the Modern-Era Retrospective analysis for Research and Applications (MERRA) and GEOS Forward Processing (GEOS-FP). We evaluate four global <span class="inline-formula"><sup>222</sup></span>Rn emission scenarios by comparing model results with observations at 51 surface sites. The default emission scenario in GEOS-Chem yields a moderate agreement with surface observations globally (68.9 % of data within a factor of 2) and a large underestimate of winter surface <span class="inline-formula"><sup>222</sup></span>Rn concentrations at Northern Hemisphere midlatitudes and high latitudes due to an oversimplified formulation of <span class="inline-formula"><sup>222</sup></span>Rn emission fluxes (1 atom cm<span class="inline-formula"><sup>−2</sup></span> s<span class="inline-formula"><sup>−1</sup></span> over land with a reduction by a factor of 3 under freezing conditions). We compose a new global <span class="inline-formula"><sup>222</sup></span>Rn emission scenario based on Zhang et al. (2011) and demonstrate its potential to improve simulated surface <span class="inline-formula"><sup>222</sup></span>Rn concentrations and seasonality. The regional components of this scenario include spatially and temporally varying emission fluxes derived from previous measurements of soil radium content and soil exhalation models, which are key factors in determining <span class="inline-formula"><sup>222</sup></span>Rn emission flux rates. However, large model underestimates of surface <span class="inline-formula"><sup>222</sup></span>Rn concentrations still exist in Asia, suggesting unusually high regional <span class="inline-formula"><sup>222</sup></span>Rn emissions. We therefore propose a conservative upscaling factor of 1.2 for <span class="inline-formula"><sup>222</sup></span>Rn emission fluxes in China, which was also constrained by observed deposition fluxes of <span class="inline-formula"><sup>210</sup></span>Pb (a progeny of <span class="inline-formula"><sup>222</sup></span>Rn). With this modification, the model shows better agreement with observations in Europe and North America (<span class="inline-formula">></span> 80 % of data within a factor of 2) and reasonable agreement in Asia (close to 70 %). Further constraints on <span class="inline-formula"><sup>222</sup></span>Rn emissions would require additional concentration and emission flux observations in the central United States, Canada, Africa, and Asia. We also compare and assess convective transport in model simulations driven by MERRA and GEOS-FP using observed <span class="inline-formula"><sup>222</sup></span>Rn vertical profiles in northern midlatitude summer and from three short-term airborne campaigns. While simulations with both GEOS products are able to capture the observed vertical gradient of <span class="inline-formula"><sup>222</sup></span>Rn concentrations in the lower troposphere (0–4 km), neither correctly represents the level of convective detrainment, resulting in biases in the middle and upper troposphere. Compared with GEOS-FP, MERRA leads to stronger convective transport of <span class="inline-formula"><sup>222</sup></span>Rn, which is partially compensated for by its weaker large-scale vertical advection, resulting in similar global vertical distributions of <span class="inline-formula"><sup>222</sup></span>Rn concentrations between the two simulations. This has important<span id="page1862"/> implications for using chemical transport models to interpret the transport of other trace species when these GEOS products are used as driving meteorology.</p>https://acp.copernicus.org/articles/21/1861/2021/acp-21-1861-2021.pdf |
| spellingShingle | B. Zhang H. Liu J. H. Crawford G. Chen T. D. Fairlie S. Chambers C.-H. Kang A. G. Williams K. Zhang D. B. Considine M. P. Sulprizio R. M. Yantosca Simulation of radon-222 with the GEOS-Chem global model: emissions, seasonality, and convective transport Atmospheric Chemistry and Physics |
| title | Simulation of radon-222 with the GEOS-Chem global model: emissions, seasonality, and convective transport |
| title_full | Simulation of radon-222 with the GEOS-Chem global model: emissions, seasonality, and convective transport |
| title_fullStr | Simulation of radon-222 with the GEOS-Chem global model: emissions, seasonality, and convective transport |
| title_full_unstemmed | Simulation of radon-222 with the GEOS-Chem global model: emissions, seasonality, and convective transport |
| title_short | Simulation of radon-222 with the GEOS-Chem global model: emissions, seasonality, and convective transport |
| title_sort | simulation of radon 222 with the geos chem global model emissions seasonality and convective transport |
| url | https://acp.copernicus.org/articles/21/1861/2021/acp-21-1861-2021.pdf |
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