Retrieval of Metop-A/IASI N2O Profiles and Validation with NDACC FTIR Data

Brice Barret,Sylvain Ferrant,Eric Le Flochmoen,Yvan Gouzenes

doi:10.3390/atmos12020219

Abstract

This paper reports atmospheric profiles of N2O retrieved from Metop/IASI with the Software for the Retrieval of IASI Data (SOFRID) for the 2008–2018 period and their validation with FTIR data from 12 stations of the Network for the Detection of Atmospheric Composition Changes (NDACC). SOFRID retrievals performed in the 2160–2218 cm−1 spectral window provide 3 independent pieces of information about the vertical profile of N2O. The FTIR versus SOFRID comparisons display a better agreement in the mid-troposphere (MT, 700–350 hPa) than in the lower (LT, Surface–700 hPa) and upper (UT, 350–110 hPa) troposphere with correlation coefficients (R) in the 0.49–0.83 range and comparable variabilities (3–5 ppbv). The agreement for oceanic and coastal stations (R > 0.77) is better than for continental ones (R < 0.72). The SOFRID MT N2O mixing ratios are significantly biased high (up to 16.8 ppbv) relative to FTIR at continental stations while the biases remain below 4.2 ppbv and mostly unsignificant when oceanic data are considered. The average MT decadal trends derived from SOFRID at the 8 NDACC stations with continuous observations during the 2008–2018 period (1.05 ± 0.1 ppbv·yr−1) is in good agreement with the corresponding FTIR trends (1.08 ± 0.1 ppbv·yr−1) and the NOAA-ESRL trends from surface in-situ measurements (0.95 ± 0.02 ppbv·yr−1). In the Northern Hemisphere where they are clearly detected, the N2O MT seasonal variations from SOFRID and FTIR are phased (summer minima) and have similar amplitudes. SOFRID also detects the UT summer maxima indicating independent MT and UT information. The global MT N2O oceanic distributions from SOFRID display low geographical variability and are mainly characterized by enhanced tropical mixing ratios relative to mid and high latitudes.

Highlights

Since 2011, Nitrous Oxide (N2 O) has become the third most important greenhouse gas (GHG) [1] whith a global warming potential about 300 times larger than CO2 over a 100 years period [2]
We report IASI N2 O profiles retrieved with the SOftware for a Fast Retrival of IASI Data (SOFRID) and their global validation with NDACC-FTIR
We have decided to focus on the Software for the Retrieval of IASI Data (SOFRID) and FTIR N2 O MT retrieved Volume Mixing Ratio (VMR)

Summary

Introduction

Since 2011, Nitrous Oxide (N2 O) has become the third most important greenhouse gas (GHG) [1] whith a global warming potential about 300 times larger than CO2 over a 100 years period [2]. As N2 O is inert in the troposphere and is not removed by dry or wet deposition or absorbed by oceanic uptake, its atmospheric lifetime is over 100 years. N2 O is emitted in the atmosphere by various sources: natural and agricultural soils, oceans, industries related to fuel combustion and biomass burning. Natural soils and oceans account for about 2/3 of the emissions (10 and 12 Tg N2 O-N yr−1 ) with the remaining third (5.3 Tg N2 O-N yr−1 ) caused by anthropogenic activities. The two most important processes responsible for N2 O soil emissions are nitrification and denitrification by microbial activity. Incomplete denitrification produces N2 O instead of N2 It occurs preferentially in undrained and anoxic soils, with an excess of nitrate, conditions often met in agricultural soils during wet seasons [5]. Denitrification has a higher yield than nitrification which is the aerobic oxydation of ammonium into nitrite and nitrate

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Conclusion