Shipborne MAX-DOAS measurements for validation of TROPOMI NO2 products

Wang, P., Piters, A., van Geffen, J., Tuinder, O., Stammes, P. and Kinne, S.: 2020,
Atmos. Meas. Tech. 13, 1413-1426.


Tropospheric NO_2 and stratospheric NO_ vertical column densities are important TROPOspheric Monitoring Instrument (TROPOMI) data products. In order to validate the TROPOMI NO2 products, KNMI Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) instruments have measured NO2 on ship cruises over the Atlantic and the Pacific oceans. The MAX-DOAS instruments have participated in five cruises on board RV Sonne (in 2017 and 2019) and RV Maria S. Merian (in 2018). The MAX-DOAS measurements were acquired over 7 months and spanned about 90° in latitude and 300 in longitude. During the cruises aerosol measurements from Microtops sun photometers were also taken. The MAX-DOAS measured stratospheric NO_2 columns between 1.5×10^15 and 3.5×10^15 molec cm^-2 and tropospheric NO_2 up to 0.6×10^15 molec cm^-2. The MAX-DOAS stratospheric NO2 vertical column densities have been compared with TROPOMI stratospheric NO_2 vertical column densities and the stratospheric NO_2 vertical column densities simulated by the global chemistry Transport Model, version 5, Massively Parallel model (TM5-MP). Good correlation is found between the MAX-DOAS and TROPOMI and TM5 stratospheric NO2 vertical column densities, with a correlation coefficient of 0.93 or larger. The TROPOMI and TM5 stratospheric NO2 vertical column densities are about 0.4×10^15 molec cm^-2 (19 %) higher than the MAX-DOAS measurements. The TROPOMI tropospheric NO2 also has good agreement with the MAX-DOAS measurements. The tropospheric NO2 vertical column density is as low as 0.5×10^15 molec cm^-2 over remote oceans.

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created: 30 March 2020
last modified: 19 August 2020