Discrete-wavelength DOAS NO 2 slant column retrievals from OMI and TROPOMI

Ruiz Villena, Cristina; Anand, Jasdeep S.; Leigh, Roland J.; Monks, Paul S.; Parfitt, Claire E.; Vande Hey, Joshua D.

The use of satellite inline-formulaNO2 data for air quality studies is increasingly revealing the need for observations with higher spatial and temporal resolution. The study of the inline-formulaNO2 diurnal cycle, global sub-urban-scale observations, and identification of emission point sources are some examples of important applications not possible at the resolution provided by current instruments. One way to achieve increased spatial resolution is to reduce the spectral information needed for the retrieval, allowing both dimensions of conventional 2-D detectors to be used to record spatial information.

In this work we investigate the use of 10 discrete wavelengths with the well-established differential optical absorption spectroscopy (DOAS) technique for inline-formulaNO2 slant column density (SCD) retrievals. To test the concept we use a selection of individual OMI and TROPOMI Level 1B swaths from various regions around the world, which contain a mixture of clean and heavily polluted areas. To discretise the data we simulate a set of Gaussian optical filters centred at various key wavelengths of the inline-formulaNO2 absorption cross section. We perform SCD retrievals of the discrete data using a simple implementation of the DOAS algorithm and compare the results with the corresponding Level 2 SCD products, namely QA4ECV for OMI and the operational TROPOMI product.

For OMI the overall results from our discrete-wavelength retrieval are in very good agreement with the Level 2 data (mean difference inline-formula<5 %). For TROPOMI the agreement is good (mean difference inline-formula<11 %), with lower uncertainty owing to its higher signal-to-noise ratio. These discrepancies can be mostly explained by the differences in retrieval implementation. There are some larger differences around the centre of the swath and over water. While further research is needed to address specific retrieval issues, our results indicate that our method has potential. It would allow for simpler, more economic satellite instrument designs for inline-formulaNO2 monitoring at high spatial and temporal resolution. Constellations of small satellites with such instruments on board would be a valuable complement to current and upcoming high-budget hyperspectral instruments.

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Ruiz Villena, Cristina / Anand, Jasdeep S. / Leigh, Roland J. / et al: Discrete-wavelength DOAS NO2 slant column retrievals from OMI and TROPOMI. 2020. Copernicus Publications.

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Rechteinhaber: Cristina Ruiz Villena et al.

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