Observation- and model-based estimates of particulate dry nitrogen deposition to the oceans

摘要: Abstract. Anthropogenic nitrogen (N) emissions to the atmosphere have increased significantly deposition of nitrate (NO3−) and ammonium (NH4+) surface waters open ocean, with potential impacts on marine productivity global carbon cycle. Global-scale understanding N oceans is reliant our ability produce validate models emission, atmospheric chemistry, transport deposition. In this work,  ∼  2900 observations aerosol NO3− NH4+ concentrations, acquired from sampling aboard ships in period 1995–2012, are used assess performance modelled concentration fields over remote ocean. Three ocean regions (the eastern tropical North Atlantic, northern Indian Ocean northwest Pacific) were selected, which density distribution observational data considered sufficient provide effective comparison model products. All these study affected by mineral dust, alters N, due uptake oxides (NOx) surfaces. Assessment requires chemical report fluxes; however, fluxes cannot be measured Modelling studies such as Atmospheric Chemistry Climate Model Intercomparison Project (ACCMIP), only flux, therefore very difficult for dry Here, available averaged a 5° × 5° grid compared ACCMIP (ModDep) oxidised (NOy) reduced (NHx) following parameters Tracer 4 Environmental Chemical Processes Laboratory (TM4): ModDep NOy, NHx particulate NH4+, surface-level concentrations. As ensemble, can expected more robust than TM4, while TM4 gives access speciated (NO3− NH4+) that relevant observed not ACCMIP. Dry (CalDep) calculated concentrations using estimates velocities. Model–observation ratios (RA, n), weighted grid-cell area number observations, models. Comparison three suggests overestimates (RA, n =  1.4–2.9) underestimates (RA, n =  0.5–0.7), spatial distributions Atlantic being reproduced model. case Ocean, discrepancy was probably seasonal biases sampling. Similar patterns various comparisons CalDep (RA, n =  0.6–2.6 NO3−, 0.6–3.1 NH4+). Values RA, n CalDep–ModDep approximately double corresponding values significant fraction gas-phase NH3 incorporated suffered scarcity large uncertainty velocities derive These uncertainties been major limitation flux material several decades. Recommendations made improvements estimation through changes modelling model–observation procedures. Validation observable aerosol-phase species' achieved if products