Long-term Global Multi-physical Modelling of Ozone Dry Deposition Velocity - with Focus on Process Uncertainty and Implication on Air Quality Modelling

Dry deposition is the second largest sink of tropospheric ozone and an important pathway for the terrestrial biosphere, and therefore meteorology and hydroclimate, to impact atmospheric chemistry. Several parameterizations for ozone dry deposition have been implemented in regional and global atmospheric chemistry models and air quality observation networks. However, these parameterizations are developed using small subsets of all published ozone flux observations with relatively short temporal coverage (often less than a year), potentially hampering their spatial-temporal representativeness and, more importantly, leading to divergent interpretations on the mechanisms affecting ozone dry deposition. We investigate the process uncertainty in simulated mean and interannual variability of ozone dry deposition velocity by driving 4 typical ozone dry deposition models with 30-years long record of assimilated meteorology (Modern-Era Retrospective analysis for Research and Application, Version 2, MERRA-2) and leaf area index (LAI3g). The simulated ozone deposition velocities are evaluated against field observations. The sensitivity of surface ozone concentration to deposition velocity is estimated using the GEOS-Chem global chemical transport model. which we use to estimate the impact of such uncertainty on surface ozone. We find that the differences in monthly mean simulated ozone deposition velocity lead to significant difference in monthly mean surface ozone (up to 10 ppbv) in most vegetated regions over the world, and the differences show seasonal variation. Both LAI and meteorology are found to contribute to the interannual variability of ozone dry deposition velocity. However, models with explicit dependence on hydroclimatic variables or plant ecophysiology are more sensitive to meteorology. The interannual variability in ozone deposition velocity generally leads to 0.5-2 ppbv of interannual variability in surface ozone, which is largely comparable with the meteorologically driven ozone variability at similar timescale. Our study highlights the importance of dry deposition parameterization as a key uncertainty in simulating ozone dry deposition and its relevance in simulation of mean and long-term interannual variability of surface ozone.