Reply to Sun et al.: Deposition of organic nitrogen

In PNAS, we (1) highlight changes in the balance of oxidized and reduced nitrogen contributions to United States reactive nitrogen deposition, pointing out that decreases in nitrogen oxides (NOx) emissions, combined with modest growth in ammonia emissions, have altered the inorganic nitrogen deposition budget from majority deposition by oxidized species (nitric acid and nitrate) in the early 1990s to majority deposition by reduced species (ammonia and ammonium) today. Our analysis was conducted using measurements of individual species concentrations and, for wet inputs, measured deposition fluxes, to overcome some of the limitations of prior analyses based on simulation by large-scale chemical … [↵][1]1To whom correspondence should be addressed. Email: collett{at}atmos.colostate.edu. [1]: #xref-corresp-1-1