What are the differences between the CAMS regional European emissions (CAMS-REG) and the official reported emission inventories?

What are the differences between the CAMS regional European emissions (CAMS-REG) and the official reported emission inventories?

Emission data are submitted by the Parties to the Convention on Long Range Transboundary Air Pollution to the EMEP programme (air pollutants) or the UNFCCC secretariat (Greenhouse gases). We refer to these emission data as official reported emissions, available from CEIP and UNFCCC, respectively. The CAMS-REG emission inventories are based to a large extent on these official EMEP & UNFCCC inventories but are not exactly the same. This note briefly explains the main differences.

The CAMS-REG emission data set uses the official UNFCCC & EMEP inventories at the most detailed level as its main input. The rational is that national experts produce the best estimate of emissions in their country. The data used are the total emissions by pollutant, sector, country and year but not the gridded data. Some modifications or adjustments are made by CAMS to the official reported emissions, for example if for a particular past year a source sector is incompletely filled we would gap fill to obtain a consistent time-series since the year 2000. Other modifications are related to bringing clarity in certain emission categories. Examples of the latter are emissions from inland shipping and agricultural waste burning, which are replaced with alternative estimates. Reported emissions are harmonized by excluding some categories that sometimes are incompletely reported, e.g., NOx emissions from agricultural soils and NMVOC from livestock. Especially for non-EU countries, the official inventories are sometimes incomplete or otherwise insufficient, and alternative estimates are used. These may come from e.g.

Instead of using the reported gridded data, with grids varying country by country, CAMS-REG uses a uniform spatial distribution of the country totals by sector to ensure consistency in the spatial distribution over the entire domain (to the extent possible). The distribution proxies are partly developed by TNO or other CAMS partners.

Altogether, this implies that for most EU countries and most sectors, the CAMS total country emissions are equal to those reported to EMEP or UNFCCC, but the spatial distribution will be different. For other countries, however, in particular non-EU countries and some specific sectors, discrepancies may be larger.

In addition, it should be noted that the EMEP & UNFCCC emissions are reported every year for all historical years. However, because of the time needed for processing and developing consistent time-series the CAMS-REG data are not annually updated and the official reported data to be used are frozen at a certain moment in time. For example, the CAMS-REG-v2 emissions dataset for 2000-2015 is based on emissions as reported in 2017, with 2015 as most recent emission year. However, in the following year (2018), official reported data for any year in the 2000-2015 time series may be adjusted but the CAMS-REG-v2 dataset will remain frozen. This means national totals in CAMS-REG-v2 may slightly differ from the latest emissions reported by countries to EMEP or UNFCCC e.g. in 2018, but are still in line with the data as reported in 2017.