Enhanced Tropospheric Ozone Assessment Through TOAR-II Multi-Chemical Reanalysis Intercomparisons

Chemical reanalysis is a systematic approach that use data assimilation to produce long-term data records of atmospheric composition consistent with model processes and observations. Like meteorological reanalysis, which has been widely used in weather and climate research, chemical reanalysis provides comprehensive information on atmospheric composition variability, enhancing our understanding of the processes controlling the atmospheric environment. Chemical reanalysis has made considerable progress in recent years and offer a unique global coverage of decadal ozone trends over the satellite data records. This presentation will highlight the following key results from the IGAC TOAR-II chemical reanalysis working group, which supports the TOAR-II and ACMAP objectives to assess the impacts of tropospheric ozone on climate, human health, and vegetation at regional to global scales:

1. Performance evaluation of reanalysis products: The latest global and regional chemical reanalysis products have been evaluated using TOAR and other observations. This evaluation provides important insights into the potential of reanalysis data for studying ozone distributions on both regional and global scales and for identifying trends in areas with sparse in-situ observations. The long-term records from chemical reanalysis data also help quantify the contributions of factors such as precursor emissions to observed ozone trends and surface ozone exceedances.
2. Values of satellite observing systems: Multiple global chemical reanalysis frameworks have been used to assess the relative impacts of assimilating satellite ozone and its precursor measurements on surface and free tropospheric ozone analyses. The results emphasize the importance of using ozone and precursor measurements simultaneously and the need to consider the impact of forecast model performance and data assimilation configurations when assessing the impacts of individual satellite measurements. This is important to provide an unbiased assessment of the value of each observing system and to guide the design of future observing systems.
3. Representativeness of ground-based measurements: Well-validated chemical reanalysis ozone fields provide a unique opportunity to improve quality control processes and evaluate the representativeness of various observational datasets. The spatial and temporal representativeness of global ground-based networks, including ozonesondes, IAGOS aircraft, FTIR, and Brewer Umkehrs, has been evaluated using chemical reanalysis data to assess their ability in representing regional ozone distributions and its long-term trends.