Dissecting the contributions of organic nitrogen aerosols to global atmospheric nitrogen deposition and implications for ecosystems.

Atmospheric deposition of particulate organic nitrogen (ON) is a significant process in the global nitrogen cycle and may be pivotally important for N-limited ecosystems. However, past models largely overlooked the spatial and chemical inhomogeneity of atmospheric ON and were thus deficient in assessing global ON impacts. We constructed a comprehensive global model of atmospheric gaseous and particulate organic nitrogen (ON), including the latest knowledge on emissions and secondary formations. Using this model, we simulated global atmospheric ON abundances consistent with observations. Our estimated global atmospheric ON deposition was 26 Tg N yr, predominantly in the form of ON (23 Tg N yr) and mostly from wildfires (37%), oceans (22%) and aqueous productions (17%). Globally, ON contributed as much as 40% to 80% of the total N deposition downwind of biomass-burning regions. Atmospheric ON deposition thus constituted the dominant external N supply to the N-limited boreal forests, tundras and the Arctic Ocean, and its importance may be amplified in a future warming climate.