Simultaneous profiling of aerosol and tropospheric nitrogen dioxide from synergetic ground-based observations of sun-sky photometer and spectrometer

Trace gasses (e.g., NO₂, SO₂, HCHO) and aerosols play an important role in atmospheric chemistry and physics. They also negatively affect human and ecosystem health. Vertical distribution of these gasses in the lower troposphere (up to 3-4 km) is often monitored using MAX-DOAS (Multi-AXis Differential Optical Absorption Spectroscopy) technique. Conversion of the trace gas slant absorption (from different viewing angles) into vertical concentration profile requires information about aerosol optical properties and their vertical distribution. Aerosol extinction coefficient profiles are retrieved from the MAX-DOAS measurements of absorption induced by oxygen collision complex (O₂O₂). The missing Information about columnar aerosol properties is typically taken, with some simplification, from the closest AERONET sun-sky photometer measurements.

This study investigates the possibility of simultaneous aerosol and tropospheric NO₂ concentration profile retrievals from synergetic ground-based observations by AERONET sun-sky photometer and Pandonia Global Network spectrometer. We consider standard AERONET sun-sky photometer measurements at 440, 675, 870, and 1020 nm, as well as, available additional observations at 340, 380, 500, and 1640 nm.

We use GRASP (Generalized Retrieval of Atmosphere and Surface Properties, Dubovik et al., 2021) to implement simultaneous retrieval of tropospheric NO₂ and vertical aerosol properties from multi-axis differential slant column densities of NO₂ and O₂O₂, and radiance measurements (almucantar and vertical scanning).

The GRASP algorithm was modified to include trace gases (NO₂, HCHO, O₂O₂) differential slant column density measurements and pseudo spherical correction of Earth curvature. In addition, a flexible gas absorption calculation based on optimized correlated k-distribution method (Momoi et al., 2022) was implemented. This presentation demonstrates advantages of synergetic observations for the aerosol and tropospheric NO₂ vertical profile retrievals in comparison to the current MAX-DOAS only inversion approaches.

 

Reference:

Dubovik, O., D. Fuertes, P. Litvinov, et al., “A Comprehensive Description of Multi- Term LSM for Applying Multiple a Priori Constraints in Problems of Atmospheric Remote Sensing: GRASP Algorithm, Concept, and Applications”, Front. Remote Sens. 2:706851. doi: 10.3389/frsen.2021.706851, 2021.

Momoi, M., H. Irie, M. Sekiguchi, et al., “Rapid, accurate computation of narrow‑band sky radiance in the 940 nm gas absorption region using the correlated k‑distribution method for sun‑photometer observations”, Prog. Earth Planet. Sci., 9, 10, 1 - 22, https://doi.org/10.1186/s40645-022-00467-6, 2022.