This dataset includes ambient atmospheric deposition data for the Bear Brook Watershed in Maine (BBWM). The BBWM consists of two watersheds, the reference East Bear (EB), receiving ambient deposition, and the treated West Bear (WB), which received experimental elevated N+S deposition for 27 years. Ambient wet deposition was collected from 1987 to 2012 using AeroChem collectors, and the measured precipitation chemistry was interpolated to calculate monthly and annual fluxes.