资源环境科技发展态势分析平台

We synthesized N₂O emissions over North America using 17 bottom-up (BU) estimates from 1980−2016 and five top-down (TD) estimates from 1998−2016. The BU-based total emission shows a slight increase owing to U.S. agriculture, while no consistent trend is shown in TD estimates. During 2007−2016, North American N₂O emissions are estimated at 1.7 (1.0−3.0) Tg N yr^-1 (BU) and 1.3 (0.9−1.5) Tg N yr^-1 (TD). Anthropogenic emissions were twice as large as natural fluxes from soil and water. Direct agricultural and industrial activities accounted for 68% of total anthropogenic emissions, 71% of which was contributed by the U.S. Our estimates of U.S. agricultural emissions are comparable to the EPA greenhouse gas (GHG) inventory, which includes estimates from IPCC tier 1 (emission factor) and tier 3 (process-based modeling) approaches. Conversely, our estimated agricultural emissions for Canada and Mexico are twice as large as the respective national GHG inventories.