Reactive nitrogen (N) is an essential nutrient for plants driving vegetation change when deposited. Portugal is one of the most nitrogen sensitive countries in the world and nitrogen deposition levels often exceed the critical load set for Portuguese ecosystems. To support policy makers, the origin of the ecosystem specific nitrogen concentration and deposition is required. The aim of this study is to build up the capacity to quantify the nitrogen concentration and deposition in Portugal and obtain a detailed source apportionment. We used the source apportionment routine of LOTOS-EUROS and tracked the contribution of emission sources for nitrogen. The labeling technique allows to trace the contributions of pre-defined source sectors to all N components. All simulations were performed for 2019. The results show that combustion processes in road transport, industry & energy production and residential heating are the most important domestic sources and show large contribution along the western and southern coasts of Portugal close to the main urban centers, like Lisbon and Porto. Emissions from international shipping show large contribution in the Atlantic Ocean and the Mediterranean Sea. Agricultural activities (manure and livestock) are important sources in the inner countryside of Portugal. Natural emissions contribute most to reactive nitrogen concentrations in the north and east of Portugal. The largest variation from day to day and between night and day were observed for road transport. Residential combustion, industry, agriculture and natural emissions show large variation between seasons.