A General Observational Strategy for Validation of Satellite NO₂ Retrievals using Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS)

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Virginia Tech

This thesis analyzes the effectiveness of spatially averaged Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements at regular azimuth angle intervals on an hourly basis to validate satellite based DOAS measurements. Off-Axis MAX-DOAS Measurements taken in Blacksburg, Virginia, between November 2021 and April 2022 with an evenly distributed set of measurements were averaged every hour and compared to Direct Sun measurements, also averaged every hour. Comparisons of the difference in average measurement from both measuring strategies, as well as the distribution standard deviations of hourly measurements suggests that the NO₂ distribution around Blacksburg is homogeneous. In order to test the effectiveness of this sampling strategy,in an inhomogeneous location, the LOTOS-EUROS high resolution (1kmx1km) chemical transport model was used to simulate profiles and vertical column densities of real measurements taken during the TROLIX'19 Field Campaign. The LOTOs-EUROS model was used to simulate vertical profiles as well as Vertical Column Densities based on real MAX-DOAS measurements as well as TROPOMI viewing geometry. While the individual ground measurements were not equal to the TROPOMI profile, the TROPOMI profile is approximately the average of the profiles of measurements made within the hour of TROPOMI overpass.

MAX-DOAS, Validation, Ground Sampling