Intercomparison of stratospheric nitrogen dioxide columns retrieved from ground-based DOAS and FTIR and satellite DOAS instruments over the subtropical Izana station

Abstract

Abstract.A 13-year analysis (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) of the NO 2 vertical column densities derived from ground-based (GB) instruments and satellites has been carried out over the Izaña NDACC (Network for the Detection of the Atmospheric Composition Change) subtropical site. Ground-based DOAS (differential optical absorption spectroscopy) and FTIR (Fourier transform infrared spectroscopy) instruments are intercompared to test mutual consistency and then used for validation of stratospheric NO 2 from OMI (Ozone Monitoring Instrument) and SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY). The intercomparison has been carried out taking into account the various differences existing in instruments, namely temporal coincidence, collocation, sensitivity, field of view, etc. The paper highlights the importance of considering an "effective solar zenith angle" instead of the actual one when comparing direct-sun instruments with zenith sky ones for a proper photochemical correction. Results show that NO 2 vertical column densities mean relative difference between FTIR and DOAS instruments is 2.8 ± 10.7 % for a.m. data. Both instruments properly reproduce the NO 2 seasonal and the interannual variation. Mean relative difference of the stratospheric NO 2 derived from OMI and DOAS is −0.2 ± 8.7 % and from OMI and FTIR is −1.6 ± 6.7 %. SCIAMACHY mean relative difference is of 3.7 ± 11.7 and −5.7 ± 11.0 % for DOAS and FTIR, respectively. Note that the days used for the intercomparison are not the same for all the pairs of instruments since it depends on the availability of data. The discrepancies are found to be seasonally dependent with largest differences in winter and excellent agreement in the spring months (AMJ). A preliminary analysis of NO 2 trends has been carried out with the available data series. Results show increases in stratospheric NO 2 columns in all instruments but larger values in those that are GB than that expected by nitrous oxide oxidation. The possible reasons for the discrepancy between instruments and the positive trends are discussed in the text.

Ground-based validation of the Copernicus Sentinel-5P TROPOMI NO<sub>2</sub> measurements with the NDACC ZSL-DOAS, MAX-DOAS and Pandonia global networks

“…Measurements are made during twilight, at sunrise, and at sunset, but only sunset measurements are used here for signal-to-noise reasons (larger NO 2 column) and as these happen closer in time to the early-afternoon overpass of S5P. NDACC intercomparison campaigns (Roscoe et al, 1999;Vandaele et al, 2005) conclude an uncertainty of about 4 %-7 % on the slant column density. After conversion of the slant column into a vertical column using a zenith-sky AMF, and for the latest version of the data processing, the uncertainty on the vertical column is estimated to be on the order of 10 %-14 % (Yela et al, 2017;Bognar et al, 2019).…”

Ground-based validation of the Copernicus Sentinel-5p TROPOMI NO<sub>2</sub> measurements with the NDACC ZSL-DOAS, MAX-DOAS and Pandonia global networks

“…Since the pioneering ages of NO 2 column measurements from space with ERS-2 GOME in the mid-1990s, ground-based UV-visible DOAS measurements at twilight have served as a reference for the validation of NO 2 total column data over unpolluted stations and of NO 2 stratospheric column data from all nadir UV-visible satellites to date (e.g., Lambert et al, 1997a, b;Petritoli et al, 2003;Celarier et al, 2008;Ionov et al, 2008;Gruzdev and Elokhov, 2010;Dirksen et al, 2011;Hendrick et al, 2011;Robles-Gonzalez et al, 2016). Here as well, S5p TROPOMI stratospheric NO 2 column data are compared to the correlative measurements acquired by ZSL-DOAS (Zenith-Scattered Light Differential Optical Absorption Spectroscopy)…”

Hemispheric asymmetry in stratospheric NO<sub>2</sub> trends

“…10, lower panel). There are multiple causes affecting the magnitude of the measured column, namely, the hour of the measurements, field of view, and vertical sensitivity (Piters et al, 2011;Robles-Gonzalez et al, 2016); however, these factors should not affect the observed trends. Table 5 displays the results of the trends from the regression model using the monthly data.…”

“…The transition between RASAS and RASAS-II required a RASAS correction due to a degradation of the detector response since mid-2006, at a rate of 4.33 % year −1 . The details of the RASAS-II instrument have been previously published in Puentedura et al (2012) and Robles-Gonzalez et al (2016). The spectrometers were installed in the top terrace of the Izaña Atmospheric Observatoy, run by the CIAI (Centro de Investigación Atmosférica de Izaña), belonging to the Agencia Estatal de Meteorología (AEMET, Spain), on the slopes of the Teide volcano, Tenerife, Canary Islands.…”