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

Ground-level ozone (O-3) is a major air pollutant that adversely affects human health and ecosystem productivity. Removal of tropospheric O-3 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 CO2, climate, and short-lived air pollutant concentrations. A new ecophysiology module was thus developed to mechanistically simulate land-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 O-3 against an observation-derived dataset known as SynFlux. Our estimated stomatal conductance and dry deposition velocity of O-3 are close to SynFlux with root-mean-squared errors (RMSEs) below 0.3 cms(-1) across different plant functional types (PFTs), despite an overall positive bias in surface O-3 concentration (by up to 16 ppbv). Representing ecophysiology was found to reduce the simulated biases in deposition fluxes from the prior model but worsen the positive biases in simulated O-3 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 O-3 simulations. The estimated global O-3 deposition flux is 864 TgO(3)yr(-1) with GEOS-Chem, and the new module decreases this estimate by 92 TgO(3)yr(-1). Estimated global gross primary production (GPP) without O-3 damage is 119 PgCyr(-1). O-3-induced reduction in GPP is 4.2 PgCyr(-1) (3.5 %). An elevated CO2 scenario (580 ppm) yields higher global GPP (+16.8 %) and lower global O3 depositional sink (-3.3 %). Global isoprene emission simulated with a photosynthesis-based scheme is 317.9 TgCyr(-1), which is 31.2 TgCyr(-1) (-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 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.