This study conducted a full two-year (2014 and 2015) measurements of dry and bulk deposition of atmospheric inorganic nitrogen (N) at the suburb of Xining city, Qinghai province. Dry N deposition fluxes were calculated by multiplying the atmospheric concentrations of NH3 and NO2 measured using passive samplers with the modeled dry deposition velocities provided by the GEOS-Chem global chemical transport model, while bulk N deposition fluxes were measured using precipitation gauge. Annual mean concentrations of gaseous NH3 and NO2 averaged 8.8 and 19.6 μg·m-3, respectively, with significantly higher values in 2015 than in 2014. Seasonal mean NH3 concentrations were higher in spring and summer than in autumn and winter, but the concentrations of NO2 changed little from season to season, with a small peak in autumn. Annual mean concentrations of NH4+-N and NO3--N in precipitation averaged 2.2 and 1.8 mg·L-1, respectively. Concentrations of NH4+-N in autumn were~55% lower than those in other seasons, whereas those of NO3--N in autumn or winter were~26% higher than those in spring and summer. Dry deposition of NH3 and NO2 was 9.0 and 2.8 kg·(hm2·a)-1, respectively. Bulk deposition of NH4+-N and NO3--N in precipitation was 7.6 and 6.2 kg·(hm2·a)-1, respectively. Reduced N (gaseous NH3 and NH4+-N in precipitation) was the dominant form of N deposition. The total dry and wet N deposition was 25.6 kg·(hm2·a)-1, which represented significant nutrient input from the environment to the suburban farmland, but this amount of deposited N exceeded the critical loads[10-20 kg·(hm2·a)-1] of terrestrial ecosystems, suggesting a risk of "N saturation" in the local natural environment.
Keywords: Tibetan Plateau; atmospheric reactive N; dry deposition; suburban area; wet deposition.