Summertime upper tropospheric nitrous oxide over the Mediterranean as a footprint of Asian emissions
Résumé
The aim of this paper is to study the transport of nitrous oxide (N$_2$O) from the Asian surface to
the eastern Mediterranean Basin (MB). We used measurements from the spectrometer Thermal and Near
infrared Sensor for carbon Observation Fourier transform spectrometer on board the Greenhouse gases
Observing SATellite (GOSAT) over the period of 2010–2013. We also used the outputs from the chemical
transport model LMDz-OR-INCA over the same period. By comparing GOSAT upper tropospheric retrievals to
aircraft measurements from the High-performance Instrumented Airborne Platform for Environmental
Research Pole-to-Pole Observations, we calculated a GOSAT High-performance Instrumented Airborne
Platform for Environmental Research standard deviation (SD error) of ~2.0 ppbv for a single pixel and a mean
bias of approximately $-$1.3 ppbv (approximately $-$0.4%). This SD error is reduced to ~0.1 ppbv when we
average the pixels regionally and monthly over the MB. The use of nitrogen fertilizer coupled with high soil
humidity during the summer Asian monsoon produces high N2O emissions, which are transported from
Asian surfaces to the eastern MB. This summertime enrichment over the eastern MB produces a maximum in
the difference between the eastern and the western MB upper tropospheric N$_2$O (east-west difference) in July
in both 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.
Domaines
Océan, Atmosphère
Origine : Publication financée par une institution