Intercomparison of slant column measurements of NO<sub>2</sub> and O<sub>4</sub> by MAX-DOAS and zenith-sky UV and visible spectrometers

Abstract

Abstract. In June 2009, 22 spectrometers from 14 institutes measured tropospheric and stratospheric NO 2 from the ground for more than 11 days during the Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments (CINDI), at Cabauw, NL (51.97 • N, 4.93 • E). All visible instruments used a common wavelength range and set of cross sections for the spectral analysis. Most of the instruments were of the multi-axis design with analysis by differential spectroscopy software (MAX-DOAS), whose nonzenith slant columns were compared by examining slopes of their least-squares straight line fits to mean values of a selection of instruments, after taking 30-min averages. Zenith slant columns near twilight were compared by fits Correspondence to: H. K. Roscoe (h.roscoe@bas.ac.uk) to interpolated values of a reference instrument, then normalised by the mean of the slopes of the best instruments. For visible MAX-DOAS instruments, the means of the fitted slopes for NO 2 and O 4 of all except one instrument were within 10% of unity at almost all non-zenith elevations, and most were within 5%. Values for UV MAX-DOAS instruments were almost as good, being 12% and 7%, respectively. For visible instruments at zenith near twilight, the means of the fitted slopes of all instruments were within 5% of unity. This level of agreement is as good as that of previous intercomparisons, despite the site not being ideal for zenith twilight measurements. It bodes well for the future of measurements of tropospheric NO 2 , as previous intercomparisons were only for zenith instruments focussing on stratospheric NO 2 , with their longer heritage.Published by Copernicus Publications on behalf of the European Geosciences Union.

Evaluation of tropospheric SO<sub>2</sub> retrieved from MAX-DOAS measurements in Xianghe, China

“…It is based on the measurement of sunlight scattered at multiple elevation angles towards the horizon, thus increasing the sensitivity to absorbers present close to the ground compared to the zenith viewing geometry (Hönninger et al, 2004). MAX-DOAS studies published so far have been mainly focused on the retrieval of NO 2 (e.g., Wittrock et al, 2004;Vlemmix et al, 2010;Frins et al, 2012;Hendrick et al, 2014;Ma et al, 2013;Wang et al, 2014), halogen oxides like BrO and IO (e.g., Frieß et al, 2011;Großmann et al, 2013), formaldehyde (e.g., Heckel et al, 2005;Wagner et al, 2011), and aerosols (e.g., Wagner et al, 2004;Frieß et al, 2006;Clémer et al, 2010). A lot of work has been done on MAX-DOAS measurements of volcanic SO 2 (e.g., Bobrowski et al, 2007;Galle et al, 2010), but so far only a few studies deal with MAX-DOAS observations of this species in polluted areas (e.g., Irie et al, 2011;Lee et al, 2008;Wu et al, 2013), despite the fact that, as for other trace gases like NO 2 , HCHO, and BrO, the combination of both surface concentration and VCD retrievals makes MAX-DOAS a useful technique for validating SO 2 satellite data.…”

Investigating differences in DOAS retrieval codes using MAD-CAT campaign data

“…The same instrumental set-up has been used in previous campaigns, e.g. CINDI and TransBrom (Roscoe et al, 2010;Peters et al, 2012).…”

“…was the first to also have a focus on MAX-DOAS observations of tropospheric species (Roscoe et al, 2010;Piters et al, 2012;Pinardi et al, 2013) and has recently been followed by the CINDI-2 campaign carried out in 2016, also in Cabauw. However, these intercomparison exercises concentrated mostly on results originating from different retrieval codes and instruments, and separation of instrument and retrieval effects was not easily possible.…”

NO<sub>2</sub> observations over the western Pacific and Indian Ocean by MAX-DOAS on <i>Kaiyo</i>, a Japanese research vessel

“…6c). Note that we also retrieved NO 2 by using the 425-490 nm window, which was used for intercomparison during the Cabauw Intercomparison campaign of Nitrogen Dioxide measuring Instruments (CINDI) campaign at Cabauw, the Netherlands (Roscoe et al, 2010). This retrieval yielded poor fitting results and negative DSCD values, as for the 425-450 nm window (figures not shown).…”

“…Irie et al, 2009Irie et al, , 2011Takashima et al, 2009Takashima et al, , 2011. The instrument has been validated with other instruments, yielding differences of less than ∼ 10 % for NO 2 and oxygen dimer (O 4 ) differential slant column densities (DSCDs) (Roscoe et al, 2010). Here, we report on the development of a MAX-DOAS instrument for use on ocean vessels, using an active-type gimbal to keep the telescope horizontal.…”