The research will use atmospheric observations of aerosol composition from the Ruisdael Observatory network in and downwind of Rotterdam harbor, and at a remote seaside monitoring station in Groningen. The primary measurement instrument used will be the Aerodyne Aerosol Chemical Speciation Monitor (ACSM) that is permanently installed at each site, as well as other complementary instrumentation which we will deploy opportunistically to focus on particular seasonal processes at available field sites throughout the project. The focus will be on the inorganic ion balance (NH4+/NO3-/SO42-) and nitrogen speciation (organic/inorganic) in ambient aerosol across this spatial gradient and seasons. Positive matrix factorization (PMF) analysis strategies will be used to apportion urban, industrial, and agricultural sources of airborne reactive nitrogen, as well as regional chemical transport models to assess their contributions to air pollution exposure for the population of the Netherlands and deposition to ecosystems.