[Dry and Bulk Nitrogen Deposition in Suburbs of Xining City]

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.