A high-resolution European emission inventory of anthropogenic direct and indirect N2O emissions

Nitrous oxide (N₂O) is the third most important long-lived greenhouse gas (GHG) and an important stratospheric ozone-depleting substance. We present the first version of a new high-resolution European emission inventory of anthropogenic direct and indirect N₂O emissions. This inventory is developed to achieve one of the special objectives of the AVENGERS project, namely to advance the provision of high-resolution prior emissions by use of innovative activity data. AVENGERS is a Research and Innovation project funded under the Horizon Europe program of the European Union whose objective is to reconcile reported GHG emissions with independent information from atmospheric observations using top-down methods and process-based models, and thereby reduce the most important uncertainties of national emission inventories. To be able to compare national reported emission data against observations and model estimates, these reported emissions need to be available in a gridded form including essential emission characteristics such as emission timing and emission height. Our emission inventory starts from the reporting by European countries in their National Inventory Reports (NIR) to UNFCCC. Emissions are collected at the highest sectoral level. Each (sub)sector is connected to a specific spatial proxy, whereafter a consistent spatial distribution is applied for Europe at a resolution of 0.05^∘ × 0.1^∘ grid resolution (~6x6km). To support inverse modelling over a longer period where measurements are available, the inventory covers the period 2010-2021. Differences in country-specific choices in emission reporting to UNFCCC, e.g., in the waste sector, may lead to inconsistent emission estimates; we provide options for harmonization of these discrepancies. We pay special attention to understanding the role of indirect N₂O emissions that may be equivalent to 15-20% of the total anthropogenic N₂O emissions. Indirect emissions involve nitrogen that is emitted by anthropogenic activities and/or removed from agricultural soils and animal waste management systems via volatilization, leaching, runoff, or harvest of crop biomass, leading to N₂O formation elsewhere. The reported indirect emissions, emitted from natural ecosystems and/or waterbodies are compared against process-model based emission estimates. The ultimate objective of this research is to reduce uncertainties in the key sources of N₂O and support the implementation of top-down methods in support of the UNFCCC’s NIR preparation in collaboration between inverse modellers and inventory compilers.