A review of indirect NO emission factors from agricultural nitrogen leaching and runoff to update of the default IPCC values.

Indirect NO emissions from agricultural nitrogen (N) leaching and runoff in water bodies contribute significantly to the global atmospheric NO budget. However, considerable uncertainty regarding this source remains in the bottom-up NO inventory. Indirect NO emission factor associated with N leaching and runoff (EF; kg NON per kg of NO-N) incorporate three components for groundwater and surface drainage (EF), rivers (EF), and estuaries (EF). The 2006 IPCC default EF value was based on a small number of studies available at the time. Here we present the synthesis of 254 measurements of EF, dissolved NO, and nitrate from 106 studies. Our results do not support the further downward revision of EF by the IPCC and suggest an upward revision of EF of 0.0060. The emission factors for groundwater and springs (0.0079) was higher than that for surface drainage (0.0040). The emission factor for lakes, ponds, and reservoirs was 0.0012, whereas that for rivers was 0.0030, and a combined EF was 0.0026. Estimated EF and EF (0.0026) values from the study were close to the current IPCC default values (0.0025 each). We estimated an updated default EF value of 0.01 for the refinement of IPCC guidelines.