...

You can use this link to directly access the data in the MARS catalogue (please remember that ecCodes version 2.28.0 or later is required to handle the full range of parameters of current CAMS data).

Atmosphere Data Store (ADS)

If you don't have access to ECMWF computers but would still like to access a large subset of test data, you can retrieve fields from the cams-global-atmospheric-composition-forecasts-test dataset using the Copernicus Atmosphere Data Store API.

...

If you haven't done it yet, you will need to create an account and accept the terms of use of Copernicus Atmosphere Data Store.

The test data is only accessible through the ADS API service, and it is not possible to use the interactive web interface to download it.

You can use existing requests for the CAMS global atmospheric composition dataset by replacing the dataset name with "cams-global-atmospheric-composition-forecasts-test".

Example

Total aerosol optical depth at 550 nm in NetCDF format, only European domain, 10 dates, day 1 forecast

...