Significant contributions of combustion-related sources to ammonia emissions

Atmospheric ammonia (NH(3)) and ammonium (NH(4)(+)) can substantially influence air quality, ecosystems, and climate. NH(3) volatilization from fertilizers and wastes (v-NH(3)) has long been assumed to be the primary NH(3) source, but the contribution of combustion-related NH(3) (c-NH(3), mainly fossil fuels and biomass burning) remains unconstrained. Here, we collated nitrogen isotopes of atmospheric NH(3) and NH(4)(+) and established a robust method to differentiate v-NH(3) and c-NH(3). We found that the relative contribution of the c-NH(3) in the total NH(3) emissions reached up to 40 ± 21% (6.6 ± 3.4 Tg N yr(−1)), 49 ± 16% (2.8 ± 0.9 Tg N yr(−1)), and 44 ± 19% (2.8 ± 1.3 Tg N yr(−1)) in East Asia, North America, and Europe, respectively, though its fractions and amounts in these regions generally decreased over the past decades. Given its importance, c-NH(3) emission should be considered in making emission inventories, dispersion modeling, mitigation strategies, budgeting deposition fluxes, and evaluating the ecological effects of atmospheric NH(3) loading.