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. Atmospheric pollution has many profound effects on humanhealth, ecosystems, and the climate. Of concern are high concentrations anddeposition of reactive nitrogen (Nr) species, especially of reduced N(gaseous NH3, particulate NH4+). Atmospheric chemistry andtransport models (ACTMs) are crucial to understanding sources and impacts ofNr chemistry and its potential mitigation. Here we undertake the firstevaluation of the global version of the EMEP MSC-W ACTM driven by WRFmeteorology (1∘×1∘ resolution),with a focus on surface concentrations and wet deposition of N and S speciesrelevant to investigation of atmospheric Nr and secondary inorganicaerosol (SIA). The model–measurement comparison is conducted both spatiallyand temporally, covering 10 monitoring networks worldwide. Model simulationsfor 2010 compared use of both HTAP and ECLIPSEE (ECLIPSE annual totalwith EDGAR monthly profile) emissions inventories; those for 2015 usedECLIPSEE only. Simulations of primary pollutants are somewhat sensitiveto the choice of inventory in places where regional differences in primaryemissions between the two inventories are apparent (e.g. China) but are muchless sensitive for secondary components. For example, the difference in modelledglobal annual mean surface NH3 concentration using the two 2010inventories is 18 % (HTAP: 0.26 µg m−3; ECLIPSEE: 0.31 µg m−3) but is only 3.5 % for NH4+ (HTAP: 0.316 µg m−3; ECLIPSEE: 0.305 µg m−3). Comparisons of 2010 and2015 surface concentrations between the model and measurements demonstrate thatthe model captures the overall spatial and seasonal variations well for themajor inorganic pollutants NH3, NO2, SO2, HNO3,NH4+, NO3-, and SO42- and their wetdeposition in East Asia, Southeast Asia, Europe, and North America. Themodel shows better correlations with annual average measurements fornetworks in Southeast Asia (mean R for seven species: R7‾=0.73),Europe (R7‾=0.67), and North America (R7‾=0.63) than in East Asia (R5‾=0.35) (data for 2015),which suggests potential issues with the measurements in the latter network.Temporally, both model and measurements agree on higher NH3concentrations in spring and summer and lower concentrations in winter. Themodel slightly underestimates annual total precipitation measurements (by13 %–45 %) but agrees well with the spatial variations in precipitation inall four world regions (0.65–0.94 R range). High correlations betweenmeasured and modelled NH4+ precipitation concentrations are alsoobserved in all regions except East Asia. For annual total wet deposition ofreduced N, the greatest consistency is in North America (0.75–0.82 R range),followed by Southeast Asia (R=0.68) and Europe (R=0.61).Model–measurement bias varies between species in different networks; forexample, bias for NH4+ and NO3- is largest in Europe andNorth America and smallest in East Asia and Southeast Asia. The greateruniformity in spatial correlations than in biases suggests that the majordriver of model–measurement discrepancies (aside from differing spatialrepresentativeness and uncertainties and biases in measurements) areshortcomings in absolute emissions rather than in modelling the atmosphericprocesses. The comprehensive evaluations presented in this study support theapplication of this model framework for global analysis of current andpotential future budgets and deposition of Nr and SIA.

Evaluation of global EMEP MSC-W (rv4.34) WRF (v3.9.1.1) model surface concentrations and wet deposition of reactive N and S with measurements