Land cover change impacts on atmospheric chemistry: simulating projected large-scale tree mortality in the United States
Land use and land cover changes impact climate and air quality by altering the exchange of trace gases between the Earth's surface and atmosphere. Large-scale tree mortality that is projected to occur across the United States as a result of insect and disease may therefore have unexplored c...
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doaj-daebfccc0147414aa27800e9d035eb5a2020-11-25T00:28:31ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242016-02-01162323234010.5194/acp-16-2323-2016Land cover change impacts on atmospheric chemistry: simulating projected large-scale tree mortality in the United StatesJ. A. Geddes0C. L. Heald1S. J. Silva2R. V. Martin3R. V. Martin4Department of Physics and Atmospheric Science, Dalhousie University, P.O. Box 15000, Halifax, Nova Scotia, B3H 4R2, CanadaDepartment of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USADepartment of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USADepartment of Physics and Atmospheric Science, Dalhousie University, P.O. Box 15000, Halifax, Nova Scotia, B3H 4R2, CanadaHarvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USALand use and land cover changes impact climate and air quality by altering the exchange of trace gases between the Earth's surface and atmosphere. Large-scale tree mortality that is projected to occur across the United States as a result of insect and disease may therefore have unexplored consequences for tropospheric chemistry. We develop a land use module for the GEOS-Chem global chemical transport model to facilitate simulations involving changes to the land surface, and to improve consistency across land–atmosphere exchange processes. The model is used to test the impact of projected national-scale tree mortality risk through 2027 estimated by the 2012 USDA Forest Service National Insect and Disease Risk Assessment. Changes in biogenic emissions alone decrease monthly mean O<sub>3</sub> by up to 0.4 ppb, but reductions in deposition velocity compensate or exceed the effects of emissions yielding a net increase in O<sub>3</sub> of more than 1 ppb in some areas. The O<sub>3</sub> response to the projected change in emissions is affected by the ratio of baseline NO<sub><i>x</i></sub> : VOC concentrations, suggesting that in addition to the degree of land cover change, tree mortality impacts depend on whether a region is NO<sub><i>x</i></sub>-limited or NO<sub><i>x</i></sub>-saturated. Consequently, air quality (as diagnosed by the number of days that 8 h average O<sub>3</sub> exceeds 70 ppb) improves in polluted environments where changes in emissions are more important than changes to dry deposition, but worsens in clean environments where changes to dry deposition are the more important term. The influence of changes in dry deposition demonstrated here underscores the need to evaluate treatments of this physical process in models. Biogenic secondary organic aerosol loadings are significantly affected across the US, decreasing by 5–10 % across many regions, and by more than 25 % locally. Tree mortality could therefore impact background aerosol loadings by between 0.5 and 2 µg m<sup>−3</sup>. Changes to reactive nitrogen oxide abundance and partitioning are also locally important. The regional effects simulated here are similar in magnitude to other scenarios that consider future biofuel cropping or natural succession, further demonstrating that biosphere–atmosphere exchange should be considered when predicting future air quality and climate. We point to important uncertainties and further development that should be addressed for a more robust understanding of land cover change feedbacks.https://www.atmos-chem-phys.net/16/2323/2016/acp-16-2323-2016.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
J. A. Geddes C. L. Heald S. J. Silva R. V. Martin R. V. Martin |
spellingShingle |
J. A. Geddes C. L. Heald S. J. Silva R. V. Martin R. V. Martin Land cover change impacts on atmospheric chemistry: simulating projected large-scale tree mortality in the United States Atmospheric Chemistry and Physics |
author_facet |
J. A. Geddes C. L. Heald S. J. Silva R. V. Martin R. V. Martin |
author_sort |
J. A. Geddes |
title |
Land cover change impacts on atmospheric chemistry: simulating projected large-scale tree mortality in the United States |
title_short |
Land cover change impacts on atmospheric chemistry: simulating projected large-scale tree mortality in the United States |
title_full |
Land cover change impacts on atmospheric chemistry: simulating projected large-scale tree mortality in the United States |
title_fullStr |
Land cover change impacts on atmospheric chemistry: simulating projected large-scale tree mortality in the United States |
title_full_unstemmed |
Land cover change impacts on atmospheric chemistry: simulating projected large-scale tree mortality in the United States |
title_sort |
land cover change impacts on atmospheric chemistry: simulating projected large-scale tree mortality in the united states |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2016-02-01 |
description |
Land use and land cover changes impact climate and air quality by
altering the exchange of trace gases between the Earth's surface and
atmosphere. Large-scale tree mortality that is projected to occur across the
United States as a result of insect and disease may therefore have unexplored
consequences for tropospheric chemistry. We develop a land use module for the
GEOS-Chem global chemical transport model to facilitate simulations involving
changes to the land surface, and to improve consistency across
land–atmosphere exchange processes. The model is used to test the impact of
projected national-scale tree mortality risk through 2027 estimated by the
2012 USDA Forest Service National Insect and Disease Risk Assessment. Changes
in biogenic emissions alone decrease monthly mean O<sub>3</sub> by up to 0.4 ppb, but reductions in deposition velocity compensate or exceed the effects of emissions yielding a net increase in O<sub>3</sub> of more than 1 ppb in some
areas. The O<sub>3</sub> response to the projected change in emissions is affected by the ratio of baseline NO<sub><i>x</i></sub> : VOC concentrations, suggesting that in addition to the degree of land cover change, tree mortality impacts depend on whether a region is NO<sub><i>x</i></sub>-limited or NO<sub><i>x</i></sub>-saturated. Consequently, air quality (as diagnosed by the number of days that 8 h average O<sub>3</sub> exceeds 70 ppb) improves in polluted environments where changes in emissions are more important than changes to dry deposition, but worsens in clean environments where changes to dry deposition are the more important term. The influence of changes in dry deposition demonstrated here underscores the need to evaluate treatments of this physical process in models. Biogenic secondary organic aerosol loadings are significantly affected across the US, decreasing
by 5–10 % across many regions, and by more than 25 % locally. Tree
mortality could therefore impact background aerosol loadings by between 0.5
and 2 µg m<sup>−3</sup>. Changes to reactive nitrogen oxide abundance
and partitioning are also locally important. The regional effects simulated
here are similar in magnitude to other scenarios that consider future biofuel
cropping or natural succession, further demonstrating that
biosphere–atmosphere exchange should be considered when predicting future
air quality and climate. We point to important uncertainties and further
development that should be addressed for a more robust understanding of land
cover change feedbacks. |
url |
https://www.atmos-chem-phys.net/16/2323/2016/acp-16-2323-2016.pdf |
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