Estimating the effect of tropospheric O3 on Gross Primary Productivity over European forests using satellite data

Abstract:

Current investigations into O₃-induced vegetation damage rely on long-term in-situ measurements of O₃ concentration and vegetation response over time, or on exposure studies via fumigation. However, such investigations are costly, time-consuming, and do not cover several ecosystems (e.g. tropics, developing countries). Of particular importance is accurately calculating stomatal conductance in order to estimate the expected O₃ dose, which in turn requires both species-specific parameters and accurate data of ambient conditions. Satellite datasets provide global long-term global monitoring of atmospheric composition and vegetation indices, spanning over 20 years of near-continuous observations. Relevant parameters to O₃-vegetation studies can be derived from these datasets after assimilation into atmospheric models. These datasets could potentially improve estimates of current and future vegetation losses by O₃ exposure.

In this work, the effect of O₃ exposure on European forest gross primary productivity (GPP) is estimated using several satellite-based datasets. Hourly O₃ concentrations over Europe during 2003-2016 are sourced from the Copernicus Atmospheric Monitoring Service (CAMS) reanalysis product, which has assimilated O₃ and precursor species concentrations from multiple satellite instruments. Hourly meteorological data is taken from the ERA5 reanalysis dataset (which assimilates satellite and in-situ data), while phenology and GPP are inferred from satellite leaf area index (LAI) measurements. Annual land cover data from the ESA Climate Change Initiative (CCI) satellite dataset is also used to identify dominant vegetation species for stomatal conductance calculation.

These datasets are used to estimate the monthly exposure-based index (AOT40) and the effective O₃ dose (PODy) based on stomatal conductance. General linear models (GLMs) are then fitted against the satellite GPP data to infer the synoptic reduction of GPP due to O₃ over different European climate zones. Additionally, these results are compared against theoretical decreases in GPP are estimated using literature response functions. Finally, these models are validated against in-situ GPP measurements from the FLUXNET network.