Changes to the IFS atmospheric composition model in support to the CAMS update for CY48R1

The Copernicus Atmosphere Monitoring Service (CAMS) provides global analyses and forecasts of atmospheric composition, relying on the Integrated Forecasting System (IFS) of ECMWF.  The CAMS global model consists of the aerosol model of the IFS, IFS-AER, which is a sectional-bulk scheme, while the chemistry scheme is based on a CB05-based carbon-bond mechanism, with the option to couple this to BASCOE-based stratospheric chemistry.

The composition model is updated regularly, aligned with updates of ECMWF’s operational meteorological model. Here we report on updates planned for the next operational version, referred to as CY48R1. This concern revisions on a large range of topics, as developed over the recent years, and therefore impacting many aspects of chemistry and aerosol composition in troposphere and stratosphere. Main aspects concern:

• Isoprene oxidation has been redefined, resulting in increased OH recycling and including a first model description of glyoxal as well as basic aromatics chemistry. 
• NOy chemistry has been updated to include HONO and the longer-lived species CH₃O₂NO₂.
• A coupling with secondary organic aerosol formation has been established, and the coupling of secondary inorganic aerosol has been revisited.
• the option to use the BASCOE-based stratospheric chemistry for operational application is actively considered.
• Dry and wet deposition parameterizations have been revisited by including a GEOS-Chem based deposition parameterization using tile fraction specific deposition velocities. 
• Aerosol dust emissions, and their optical properties have been revised.
• The emissions handling has been updated, along with updates of the CAMS global emission inventories themselves.

The updates of the composition model and its emissions are tested in combination with updates to the tracer transport and data assimilation aspects, and the optimal configuration will be selected for operational application.

In this contribution we provide an overview of expected changes with emphasis on changes in composition modeling aspects. We will present the subsequent impacts on key atmospheric composition aspects, including air quality performance for major pollution regions across the world, aerosol optical depth, dust, and stratospheric composition products.