Development of an ecophysiology module in the GEOS-Chem chemical transport model version 12.2.0 to represent biosphere–atmosphere fluxes relevant for ozone air quality
<p>Ground-level ozone (<span class="inline-formula">O<sub>3</sub></span>) is a major air pollutant that adversely affects human health and ecosystem productivity. Removal of tropospheric <span class="inline-formula">O<sub>3</sub><...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-05-01
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| Series: | Geoscientific Model Development |
| Online Access: | https://gmd.copernicus.org/articles/16/2323/2023/gmd-16-2323-2023.pdf |
| Summary: | <p>Ground-level ozone (<span class="inline-formula">O<sub>3</sub></span>) is a major air pollutant that adversely affects human health and ecosystem productivity. Removal of tropospheric
<span class="inline-formula">O<sub>3</sub></span> by plant stomatal uptake can in turn cause damage to plant tissues with ramifications for ecosystem and crop health. In many
atmospheric and land surface models, the functionality of stomata opening is represented by a bulk stomatal conductance, which is often
semi-empirically parameterized and highly fitted to historical observations. A lack of mechanistic linkage to ecophysiological processes such as
photosynthesis may render models inadequate to represent plant-mediated responses of atmospheric chemistry to long-term changes in <span class="inline-formula">CO<sub>2</sub></span>,
climate, and short-lived air pollutant concentrations. A new ecophysiology module was thus developed to mechanistically simulate land<span class="inline-formula">−</span>atmosphere
exchange of important gas species in GEOS-Chem, a chemical transport model widely used in atmospheric chemistry studies. The implementation not only
allows for dry deposition to be coupled with plant ecophysiology but also enables plant and crop productivity and functions to respond dynamically to
atmospheric chemical changes. We conduct simulations to evaluate the effects of the ecophysiology module on simulated dry deposition velocity and
concentration of surface <span class="inline-formula">O<sub>3</sub></span> against an observation-derived dataset known as SynFlux. Our estimated stomatal conductance and dry deposition
velocity of <span class="inline-formula">O<sub>3</sub></span> are close to SynFlux with root-mean-squared errors (RMSEs) below 0.3 <span class="inline-formula">cm s<sup>−1</sup></span> across different plant functional
types (PFTs), despite an overall positive bias in surface <span class="inline-formula">O<sub>3</sub></span> concentration (by up to 16 <span class="inline-formula">ppbv</span>). Representing ecophysiology was
found to reduce the simulated biases in deposition fluxes from the prior model but worsen the positive biases in simulated <span class="inline-formula">O<sub>3</sub></span>
concentrations. The increase in positive concentration biases is mostly attributable to the ecophysiology-based stomatal conductance being generally
smaller (and closer to SynFlux values) than that estimated by the prior semi-empirical formulation, calling for further improvements in non-stomatal
depositional and non-depositional processes relevant for <span class="inline-formula">O<sub>3</sub></span> simulations. The estimated global <span class="inline-formula">O<sub>3</sub></span> deposition flux is
864 <span class="inline-formula">Tg O<sub>3</sub> yr<sup>−1</sup></span> with GEOS-Chem, and the new module decreases this estimate by 92 <span class="inline-formula">Tg O<sub>3</sub> yr<sup>−1</sup></span>. Estimated global gross
primary production (GPP) without <span class="inline-formula">O<sub>3</sub></span> damage is 119 <span class="inline-formula">Pg C yr<sup>−1</sup></span>. <span class="inline-formula">O<sub>3</sub></span>-induced reduction in GPP is 4.2 <span class="inline-formula">Pg C yr<sup>−1</sup></span>
(3.5 %). An elevated <span class="inline-formula">CO<sub>2</sub></span> scenario (580 <span class="inline-formula">ppm</span>) yields higher global GPP (<span class="inline-formula">+</span>16.8 %) and lower global <span class="inline-formula">O<sub>3</sub></span>
depositional sink (<span class="inline-formula">−</span>3.3 %). Global isoprene emission simulated with a photosynthesis-based scheme is 317.9 <span class="inline-formula">Tg C yr<sup>−1</sup></span>, which is
31.2 <span class="inline-formula">Tg C yr<sup>−1</sup></span> (<span class="inline-formula">−</span>8.9 %) less than that calculated using the MEGAN
(Model of Emissions of Gases and Aerosols from Nature) emission algorithm. This new model development dynamically
represents the two-way interactions between vegetation and air pollutants and thus provides a unique capability in evaluating vegetation-mediated
processes and<span id="page2324"/> feedbacks that can shape atmospheric chemistry and air quality, as well as pollutant impacts on vegetation health, especially for any
timescales shorter than the multidecadal timescale.</p> |
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| ISSN: | 1991-959X 1991-9603 |