Evaluation and Global-Scale Observation of Nitrous Oxide from IASI on Metop-A

Rémi Chalinel,Jean-Luc Attié,Yannick Kangah,Philippe Ricaud,Rona Thompson,Didier Hauglustaine,Jérôme Vidot

doi:10.3390/rs14061403

Abstract

Nitrous oxide (N2O) is a greenhouse gas difficult to estimate by satellite because of its weak spectral signature in the infra-red band and its low variability in the troposphere. Nevertheless, this study presents the evaluation of new tropospheric N2O observations from the Infrared Atmospheric Sounder Interferometer (IASI) on Metop-A using the Toulouse N2O Retrieval Version 2.0 tool. This tool is based on the Radiative Transfer for Tiros Operational Vertical sounder (RTTOV) model version 12.3 coupled to the Levenberg-Marquardt optimal estimation method enabling the simultaneous retrieval of methane, water vapour, temperature profiles together with surface temperature and emissivity within the 1240–1350 cm−1 window. In this study, we focused on the upper troposphere (300 hPa) where the sensitivity of IASI is significant. The IASI N2O data has been evaluated using aircraft N2O observations from the High-performance Instrumented Airborne Platform for Environmental Research Pole-to-Pole Observations (HIPPO) campaigns in 2009, 2010, and 2011 and from the National Oceanic and Atmospheric Administration’s (NOAA) Global Greenhouse Gas Reference Network (GGGRN) in 2011. In addition, we evaluated the IASI N2O using ground-based N2O measurements from 9 stations belonging to the Network for the Detection of Atmospheric Composition Change (NDACC). We found a total random error of ∼2 ppbv (0.6%) for one single retrieval at 300 hPa. Under favorable conditions, this error is also found in the vertical level pressure range 300–500 hPa. It decreases rapidly to ∼0.4 ppbv (0.1%) when we average on a 1° × 1° box. In addition, independent observations allows the estimation of bias with the IASI TN2OR v2.0 N2O. The bias between IASI and aircraft N2O data at 300 hPa is ∼1.0 ppbv (∼0.3%). We found an estimated random error of ∼2.3 ppbv (∼0.75%). This study also shows relatively high correlations between IASI data and aircraft in situ profiles but more varying correlations over the year 2011 depending on the location between IASI and NDACC remote sensing data. Finally, we present daily, monthly, and seasonal IASI N2O horizontal distributions in the upper troposphere as well as cross sections for different seasons that exhibit maxima in the Tropical band especially over Africa and South America.

Highlights

In order to study the sensitivity profile of the Infrared Atmospheric Sounder Interferometer (IASI) nitrous oxide (N2 O) measurements, we present an example of the vertical distribution of averaging kernels, different errors and contamination factors (see Equation (3)) over France in summer daytime (Figure 6)
Toulouse N2 O Retrieval (TN2 OR) has been applied to the IASI pixels in time (±12 h) and space coincidence (±200 km) with the location and time observation of the aircraft profiles
All the aircraft profiles were convolved with the appropriate IASI averaging kernels following Equation (3) in which x is the N2 O aircraft profile and is considered as the truth

Summary

Introduction

2022, 14, 1403 contributing to global warming [2]. It has a global warming potential 296 times higher than that of CO2 on a mass basis over a 100-year horizon. N2 O emissions increased by 0.25–0.30% yr−1 over the past 10 years [4] and are very likely to keep increasing until 2100 [2] in the majority of socio-economic scenarios. There is a smaller source of abiotic emission through incomplete combustion and some industrial processes. About 57% of the global total emission of N2 O (∼17 TgN yr−1 ) is naturally occurring and the remaining is anthropogenic [4]. Anthropogenic emissions are dominated by agriculture (∼52%) and are due to the perturbation of the nitrogen cycle through the addition of nitrogen in synthetic fertilizers and manure, while industrial and fossil fuel combustion contributes ∼27% [4]

Methods

Results

Conclusion