Dry deposition fluxes of NH4+-N and NO3--N at a rural site of Indo-Gangetic Plain, India

The world’s acute reactive nitrogen (Nr) deposition is chronically eroding the biospheric integrity and undermining earth system’s resilience to be in an accommodatable state. The present study comprehensively attempts to decipher the dry depositions of atmospheric inorganic Nr along with other major ions through dustfall fluxes. Authentic atmospheric dust samples were collected by incorporating a surrogate-surface approach at an agriculturally intensive rural site in Indo-Gangetic plain of India over a year-long temporal scale from October 2017-September 2018. The mean (±Standard Error) dry deposition fluxes of NH₄⁺-N and NO₃^--N during the whole study period were observed as 0.41±0.09 kg ha^-1 yr^-1 and 6.51±1.58 kg ha^-1 yr^-1, respectively. The total percent ionic contribution to the dustfall flux was observed 2.95% and the descending order of their percent contribution in total ionic fluxes were observed as SO₄^2- (31.46%) > Cl^- (15.74%) > K⁺ (15.04%) > Ca²⁺ (13.97%) > Na⁺ (10.23 %) > NO₃^- (7.06%) > Mg²⁺ (4.43%) > F^-(1.62%) > NH₄⁺ (0.44%). The relative dominance of NO₃^--N over NH₄⁺-N fluxes was maintained in all seasons during the whole monitoring period which could be attributed to the competitive exclusion of NH₄⁺-N from acid-base neutralization reactions by other strong base cations in dustfall. Size-distribution and morphological analysis of dust particles from Scanning Electron Microscope images signified the anthropogenic involvement in shaping the dominant mode of particle-size distribution in dust fall fluxes which culminated into the dominance of fine-mode fraction over course-mode in dustfall.