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 (N) and sulphur (S) in Canada and the United States by fusion of observed and modeled data. Optimal interpolation methods are used to integrate seasonally-averaged surface concentrations of gaseous, particulate, and precipitation species into concentration fields predicted by 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 an interpolation of the difference between the modeled and measured values at network observation sites. Gas and particulate OA concentration fields are then combined with effective deposition velocities from GEM-MACH to calculate dry deposition. Similarly, OA concentrations of precipitation ions are combined with precipitation amounts from the Canadian Precipitation Analysis (CaPA) to calculate wet deposition. CaPA is also an objective analysis where all available precipitation data sets are fused with precipitation amounts predicted by GEM. Results from the 2010 development year are compared with previously-generated wet deposition kriging maps, results from the US EPA’s Total Deposition (TDEP) method, and independent validation performed with surface measurements not used in the analysis where available.