Changes to the IFS atmospheric composition model in support to the CAMS update for CY49R1.

The Integrated Forecasting System (IFS) of ECMWF is core of the Copernicus Atmosphere Monitoring Service (CAMS) to provide global analyses and forecasts of atmospheric composition, including reactive gases, as well as aerosol and greenhouse gases. 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 operational version after next, referred to as CY49R1. This concerns 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:

• A review of the representation of polar stratospheric clouds and of their impact on stratospheric ozone,
• An extension of IFS-AER to represent stratospheric sulfate aerosols, coupled with CB05 and BASCOE precursor gases,
• An upgrade of gas-particle partitioning through the implementation of EQSAM4Clim in the IFS,
• Computation of aerosol, cloud and rain pH, and use of the update pH values in aqueous chemistry,
• A combined representation of aerosols and chemistry deposition processes (wet and dry),
• Update of aerosol optics, including a simple representation of dust asphericity and hygroscopic growth,
• Update of PM diagnostic output

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