Total nitrogen deposition by measurement-model fusion using ADAGIO

Environment and Climate Change Canada's ADAGIO project (Atmospheric Deposition Analysis Generated by optimal Interpolation from Observations) generates maps of wet, dry and total annual deposition of oxidized and reduced nitrogen, as well as sulphur and ozone, in Canada and the United States by fusion of observed and modeled data. Optimal interpolation is used to integrate seasonally-averaged measurements with forecasts of surface concentration fields of gaseous, particulate, and precipitation species. Forecasts are taken from Environment and Climate Change Canada's in-line regional air quality model GEM-MACH (Global Environmental Multiscale model - Modelling Air quality and Chemistry). The result, a product called objective analysis (OA), corresponds to the forecast field adjusted by an interpolation of the difference between it and the measurements. Gas and particulate OA concentration fields are then combined with effective deposition velocities from GEM-MACH to calculate dry deposition fields. Similarly, precipitation-ion OA concentration fields are combined with gridded precipitation amounts from the Canadian Precipitation Analysis (CaPA) to calculate wet deposition fields. CaPA is a separate OA product, blending gauge measurements and radar estimates with the forecast from GEM, the operational weather prediction model. The final deposition maps provide total nitrogen deposition estimates at 10 km horizontal resolution which combine the continuous spatial and temporal coverage of the model with the accuracy of ground-based monitors. Results from the 2010 development year are compared with results from the US EPA's Total Deposition (TDep) method and with critical loads of atmospheric deposition across North America.