Industrial and agricultural ammonia point sources exposed.

Through its important role in the formation of particulate matter, atmospheric ammonia affects air quality and has implications for human health and life expectancy. Excess ammonia in the environment also contributes to the acidification and eutrophication of ecosystems and to climate change. Anthropogenic emissions dominate natural ones and mostly originate from agricultural, domestic and industrial activities. However, the total ammonia budget and the attribution of emissions to specific sources remain highly uncertain across different spatial scales. Here we identify, categorize and quantify the world's ammonia emission hotspots using a high-resolution map of atmospheric ammonia obtained from almost a decade of daily IASI satellite observations. We report 248 hotspots with diameters smaller than 50 kilometres, which we associate with either a single point source or a cluster of agricultural and industrial point sources-with the exception of one hotspot, which can be traced back to a natural source. The state-of-the-art EDGAR emission inventory mostly agrees with satellite-derived emission fluxes within a factor of three for larger regions. However, it does not adequately represent the majority of point sources that we identified and underestimates the emissions of two-thirds of them by at least one order of magnitude. Industrial emitters in particular are often found to be displaced or missing. Our results suggest that it is necessary to completely revisit the emission inventories of anthropogenic ammonia sources and to account for the rapid evolution of such sources over time. This will lead to better health and environmental impact assessments of atmospheric ammonia and the implementation of suitable nitrogen management strategies.