# Representations of SO2 and SO4 in CAMS reanalysis

**URL:** <https://forum.ecmwf.int/t/representations-of-so2-and-so4-in-cams-reanalysis/1545>\
**Category:** CAMS - Datasets and Usage\
**Tags:** cams, eac4, global\_reanalysis\
**Created:** [28 April 2020 11:04 UTC](https://forum.ecmwf.int/t/representations-of-so2-and-so4-in-cams-reanalysis/1545 "2020-04-28T11:04:09Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Michela](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/m/898d66/32.png) [@Michela](https://forum.ecmwf.int/u/Michela)\
**Post date:** [28 April 2020 11:04 UTC](https://forum.ecmwf.int/t/representations-of-so2-and-so4-in-cams-reanalysis/1545/1 "2020-04-28T11:04:09Z")

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Before the[Implementation of IFS cycle 46r1](https://confluence.ecmwf.int/display/COPSRV/Implementation+of+IFS+cycle+46r1), there were two separate CAMS Global archived analysis and forecast daily representations of SO2 and SO4: one as part of the aerosol scheme, and one as part of the gas-phase chemistry.

For aerosol-related purposes, it's recommended to use "aermr11" as sulphate aerosol, and "aermr12" as its SO2 precursor.

For gas chemistry purposes, the "so2" parameter represents SO2 in a way that's fully coupled with the rest of the gas chemistry (oxidants etc.). However, the accompanying "so4" parameter is not generally recommended for use.

From the[Implementation of IFS cycle 46r1](https://confluence.ecmwf.int/display/COPSRV/Implementation+of+IFS+cycle+46r1) in July 2019 onwards, these representations have been unified so that the aerosol and chemistry schemes are properly coupled, and only **"so2"** and **"aerm11"** should be used.