Validation of TROPOMI tropospheric NO<sub>2</sub> columns using dual-scan multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Uccle, Brussels
<p>Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of aerosols and tropospheric nitrogen dioxide (<span class="inline-formula">NO<sub>2</sub></span>) were carried out in Uccle (50.8<span class="inline-formul...
| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-10-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/13/5165/2020/amt-13-5165-2020.pdf |
| Summary: | <p>Ground-based multi-axis differential optical absorption spectroscopy
(MAX-DOAS) measurements of aerosols and tropospheric nitrogen dioxide
(<span class="inline-formula">NO<sub>2</sub></span>) were carried out in Uccle (50.8<span class="inline-formula"><sup>∘</sup></span> N, 4.35<span class="inline-formula"><sup>∘</sup></span> 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<span class="inline-formula"><sup>∘</sup></span>). By applying a vertical profile inversion algorithm in the
main azimuthal direction and a parameterization technique in the other
azimuthal directions, near-surface <span class="inline-formula">NO<sub>2</sub></span> 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 <span class="inline-formula">NO<sub>2</sub></span> around the measurement site and studying
its seasonal variations. Furthermore, we show that measuring the
tropospheric <span class="inline-formula">NO<sub>2</sub></span> 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
<span class="inline-formula">NO<sub>2</sub></span> vertical profile information derived from the MAX-DOAS
measurements, we also resolve a systematic underestimation in S5P <span class="inline-formula">NO<sub>2</sub></span>
data due to the use of inadequate a priori <span class="inline-formula">NO<sub>2</sub></span> profile shape data in the satellite retrieval.</p> |
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| ISSN: | 1867-1381 1867-8548 |