Validation of TROPOMI tropospheric NO₂ columns using dual-scan multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Uccle, Brussels

Abstract

Abstract. Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of aerosols and tropospheric nitrogen dioxide (NO2) were carried out in Uccle (50.8∘ N, 4.35∘ E), Brussels, during 1 year from March 2018 until March 2019. The instrument was operated in both the UV and visible wavelength ranges in a dual-scan configuration consisting of two sub-modes: (1) an elevation scan in a fixed viewing azimuthal direction (the so-called main azimuthal direction) pointing to the northeast and (2) an azimuthal scan in a fixed low elevation angle (2∘). By applying a vertical profile inversion algorithm in the main azimuthal direction and a parameterization technique in the other azimuthal directions, near-surface NO2 volume mixing ratios (VMRs) and vertical column densities (VCDs) were retrieved in 10 different azimuthal directions. The dual-scan MAX-DOAS dataset allows for partly resolving the horizontal distribution of NO2 around the measurement site and studying its seasonal variations. Furthermore, we show that measuring the tropospheric NO2 VCDs in different azimuthal directions improves the spatial colocation with measurements from the Sentinel-5 Precursor (S5P), leading to a reduction of the spread in validation results. By using NO2 vertical profile information derived from the MAX-DOAS measurements, we also resolve a systematic underestimation in S5P NO2 data due to the use of inadequate a priori NO2 profile shape data in the satellite retrieval.

Assessment of NO2 Pollution Level during the COVID-19 Lockdown in a Romanian City

“…To create the NO 2 maps, we used the offline high-resolution imagery NO 2 concentrations datasets by Sentinel-5P OFFL NO 2 (Offline Nitrogen Dioxide, L3), available via the Earth Engine Data Catalog [ 37 ]. TROPOMI is a passive imaging spectrometer onboard the S5P satellite platform, covering the UV–visible, NIR, and shortwave IR spectral ranges [ 38 ], and measures the atmospheric composition using a pixel size of 7 × 3.5 km 2 [ 39 ]. The tropospheric NO 2 algorithm uses a retrieval–assimilation modeling system based on the 3D global TM5 chemistry transport model [ 39 ].…”

“…TROPOMI is a passive imaging spectrometer onboard the S5P satellite platform, covering the UV–visible, NIR, and shortwave IR spectral ranges [ 38 ], and measures the atmospheric composition using a pixel size of 7 × 3.5 km 2 [ 39 ]. The tropospheric NO 2 algorithm uses a retrieval–assimilation modeling system based on the 3D global TM5 chemistry transport model [ 39 ]. The TROPOMI NO 2 data used in this paper are based on the algorithm developments for the DOMINO-2 product and for the EU QA4ECV NO 2 .…”

“…The resolution of the used data is 0.01 arc degrees. More details about the algorithm calculation of TROPOMI OFFL NO 2 L3 are presented in [ 37 , 38 , 39 ].…”

Meteorological Drivers of Permian Basin Methane Anomalies Derived from TROPOMI

“…Other studies, comparing aircraft-and ground-based spectrometer measurements in urban and non-urban areas. have also found a systematic underestimation in TROPOMI NO 2 measurements, particularly during highly polluted conditions [34,[41][42][43][44][45].…”

An improved tropospheric NO<sub>2</sub> column retrieval algorithm for TROPOMI over Europe

“…For the Uccle site, which is located south of Brussels at a distance of ∼6 km from the city center, the tropospheric NO 2 columns increase by up to 4% outwards until 6 km due to the influence of the surrounding emission sources during summer and autumn. This effect is additionally influenced by the seasonal wind pattern, particularly for winter, when the wind is blowing in the direction of the site from north (Dimitropoulou et al, 2020).…”