A synthesis of nitric oxide emissions across global fertilized croplands from crop-specific emission factors

Nitrogen (N)-fertilizer application to agricultural soils results in substantial emissions of nitric oxide (NO), a key substance in tropospheric chemistry involved in climate forcing and air pollution. However, estimates of global cropland NO emissions remain uncertain due to a lack of information on direct NO emission factors (EFds) of applied N for variours cropping systems at seasonal or annual scales. Here we quantified the crop-specific seasonal and annual-scale NO EFds through synthesizing 1094 measurements from 125 field-based studies worldwide. The global mean crop-specific seasonal EFd was 0.53%, with the highest for vegetables (0.75%). Among cereal crops, the EFd of maize (0.45%) or wheat (0.47%) was about three-times higher than for rice (0.12%). At annual scale, the mean EFd across all cropping systems was 0.58%, with tea plantations having the highest (1.54%). For other cropping systems, the annual-scale EFds ranged from 0.02% to 1.07%. Besides crop type, also soil organic ...