Summertime upper tropospheric nitrous oxide over the Mediterranean as a footprint of Asian emissions

The aim of this paper is to study the transport of nitrous oxide (N2O) from the Asian surface to the eastern Mediterranean Basin(MB). We used measurements from the spectrometer TANSO/FTS on board the Greenhouse gases Observing SATellite (GOSAT) over the period 2010-2013. We also used the outputs from the chemical transport modelLMDz-OR-INCA over the same period. By comparing GOSAT upper tropospheric retrievals to aircraft measurements from the HIAPER Pole-to-Pole Observations, we calculated a GOSAT-HIPPO standard deviation (std error) of ~2.0 ppbv for a single pixel and a mean bias of ~ -1.3 ppbv (~-0.4%). This std error is reduced to ~0.1 ppbv when we average the pixels regionally and monthly over the MB. The use of nitrogen fertilizer coupled with high soil humidity during the summer Asian monsoon produces high N2O emissions, which are transported from Asian surfaces to the eastern MB. This summertime enrichment over the eastern MB produces a maximum in the difference between the eastern and the western MB upper tropospheric N2O (east-west difference) in July both in the measurements and the model. N2O over the eastern MB can therefore be considered as a footprint of Asian summertime emissions. However, the peak-to-peak amplitude of the east-west difference observed by GOSAT (~1.4 ± 0.3 ppbv) is larger than that calculated by LMDz-OR-INCA (~0.8 ppbv). This is due to an underestimation of N2O emissions in the model and to a relatively coarse spatial resolution of the model that tends to underestimate the N2O accumulation into the Asian monsoon anticyclone.