IASI nitrous oxide (N2O) retrievals: validation and application to transport studies at daily time scales

Yannick Kangah, Philippe Ricaud, Jean-Luc Attié, Naoko Saitoh, Jérôme Vidot, Pascal Brunel, Samuel Quesada-Ruiz
2018 Atmospheric Measurement Techniques Discussions  
<p><strong>Abstract.</strong> The aim of this paper is to present a method to retrieve nitrous oxide (N<sub>2</sub>O) vertical profiles from the Infrared Atmospheric Sounding Interferometer (IASI) onboard the MetOp platform. We retrieved N<sub>2</sub>O profiles using IASI clear sky radiances in 2 spectral bands: B1 and B2 centered at ∼<span class="thinspace"></span>1280<span class="thinspace"></span>cm<sup>&amp;minus;1</sup> and ∼<span class="thinspace"></span>2220<span
more » ... cm<sup>&amp;minus;1</sup>, respectively. Both retrievals in B1 and B2 (hereafter referred to as N<sub>2</sub>O_B1 and N<sub>2</sub>O_B2, respectively) are sensitive to the mid-to-upper troposphere with a maximum of sensitivity at around 309<span class="thinspace"></span>hPa. The degrees of freedom for N<sub>2</sub>O_B1 and N<sub>2</sub>O_B2 are 1.38 and 0.93, respectively. We validated the retrievals using the High-performance Instrumented Airborne Platform for Environmental Research Pole-to-Pole Observations (HIPPO). The comparisons between HIPPO and the two retrieved datasets show relatively low standard deviation errors around 1.5<span class="thinspace"></span>% (∼<span class="thinspace"></span>4.8<span class="thinspace"></span>ppbv) and 1.0<span class="thinspace"></span>% (∼<span class="thinspace"></span>3.2<span class="thinspace"></span>ppbv) for N<sub>2</sub>O_B1 and N<sub>2</sub>O_B2, respectively. However, the impact of H<sub>2</sub>O contamination on N<sub>2</sub>O_B1 due to its strong absorption bands in B1 significantly degrades the quality of the retrievals in tropical regions. We analysed the scientific consistency of the retrievals at 309<span class="thinspace"></span>hPa with a focus on the long-range transport of N<sub>2</sub>O especially during the Asian summer monsoon. Over the mid-latitude regions, both variations of N<sub>2</sub>O_B1 and N<sub>2</sub>O_B2 at 309<span class="thinspace"></span>hPa are influenced by the stratospheric N<sub>2</sub>O-depleted air because of the relative coarse shape of the averaging kernel. The analysis of N<sub>2</sub>O_B2 using results from backtrajectories exhibits the capacity of these retrievals to capture long-range transport of air masses from Asia to northern Africa via the summer monsoon anticyclone on a daily basis. Thus, N<sub>2</sub>O_B1 and N<sub>2</sub>O_B2 offer an unprecedented possibility to study global upper tropospheric N<sub>2</sub>O on a daily basis.</p>
doi:10.5194/amt-2018-21 fatcat:2pyi6z6rdnhczldp63ciccwwiu