It is feasible for widely distributed mosses to monitor atmospheric nitrogen deposition in northern China, a global hotspot of atmospheric nitrogen pollution. Based on the nitrogen contents and nitrogen isotope values of mosses collected at Mengshan, Shandong Province in 2012, 2018 and 2022, we established a bottom-up method to calculate local atmospheric nitrogen deposition levels and source contributions. Moss nitrogen contents increased from 1.9 ± 0.2% in 2012 to 2.1 ± 0.4% in 2018, and to 2.4 ± 0.3% in 2022. On the contrary, moss nitrogen isotope values decreased from −7.5 ± 1.5‰ in 2012 to −8.6 ± 1.6‰ in 2018 and to −9.6 ± 1.3‰ in 2022. From 2012 to 2022, the total nitrogen deposition fluxes increased significantly (from 34.2 to 39.9 kg N ha⁻¹ yr⁻¹), especially the fluxes of ammonium-nitrogen deposition increased. Based on the results of Bayesian stable isotope analysis, volatilization-related ammonia (mainly from fertilizer applications and wastes) was predominant in ammonium-nitrogen deposition in the last decade. Fossil fuel nitrogen oxides contributed more than non-fossil fuel nitrogen oxides to nitrate-nitrogen deposition. Our results reveal that it is urgent to control volatilization-related ammonia and fossil fuel nitrogen oxides emission sources, which are the major contributors to atmospheric nitrogen deposition in the Mengshan area.