Shipborne MAX-DOAS measurements for validation of TROPOMI NO<sub>2</sub> products

Abstract

Abstract. Tropospheric NO2 and stratospheric NO2 vertical columns are important TROPOMI data products. In order to validate the TROPOMI NO2 products, KNMI 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 R.V. Sonne (in 2017 and 2019) and R.V. Maria S. Merian (in 2018). The MAX-DOAS measurements were acquired in 7 months and spanned about 300° in longitude and 90° in latitude. During the cruises there were also aerosol measurements from Microtops sun-photometers. The MAX-DOAS measured stratospheric NO2 columns between 1.5 × 1015 and 3.5 × 1015 molec cm-2, and tropospheric NO2 up to 0.6 × 1015 molec cm-2. The MAX-DOAS stratospheric NO2 vertical columns have been compared with TROPOMI stratospheric NO2 vertical columns and the stratospheric NO2 vertical columns simulated by TM5-MP model. Good correlation is found between the MAX-DOAS and TROPOMI and TM5 stratospheric NO2 vertical columns, with a correlation coefficient of 0.93 or larger. The TROPOMI and TM5 stratospheric NO2 vertical columns are about 0.4 × 1015 molec cm-2 higher than the MAX-DOAS measurements. The TROPOMI tropospheric NO2 has also good agreement with the MAX-DOAS measurements. The tropospheric NO2 vertical columns is as low as 0.5 × 1015 molec cm-2 over remote oceans.

Unraveling pathways of elevated ozone induced by the 2020 lockdown in Europe by an observationally constrained regional model using TROPOMI

“…Based on these results, we assume a low bias of 37 % can be mitigated by ~ 12 % through the use of high spatial resolution profiles, for a resulting total low bias of 25 %. This bias is likely not valid over pristine areas, where validation studies show lower biases in TROPOMI NO 2 ( Verhoelst et al, 2021 ; P. Wang et al, 2020 ; Zhao et al, 2020 ); nonetheless, we previously observed in Souri et al (2020a) that the low signal-to-noise ratios of those column amounts resulted in small changes in the top-down emissions. We assume the errors of observations originate from two main sources: (i) the precision error provided with the data ( e precision ) and (ii) a fixed error estimated from comparisons to in situ measurements ( e const ).…”