Abstract
Abstract. Tropospheric NO2 and stratospheric NO2 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 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 column densities have been compared with TROPOMI stratospheric NO2 vertical column densities and the stratospheric NO2 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 0.4×1015 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 0.5×1015 molec cm−2 over remote oceans.
Highlights
Nitrogen dioxide (NO2) and nitrogen oxide (NO) – usually referred to as nitrogen oxides (NOx = NO + NO2) – are airpolluting trace gases in the troposphere
In this paper we show the results of the MAX-Differential Optical Absorption Spectroscopy (DOAS) measurements during the five cruises and compare the MAXDOAS measurements with the TROPOspheric Monitoring Instrument (TROPOMI) measurements and TM5-MP model simulations
The stratospheric NO2 vertical column densities (VCDs) derived from different elevation angles are quite close to each other, but the VCDs are slightly larger at small elevation angles
Summary
Nitrogen dioxide (NO2) and nitrogen oxide (NO) – usually referred to as nitrogen oxides (NOx = NO + NO2) – are airpolluting trace gases in the troposphere. Tropospheric NO2 is mostly produced at high temperatures in combustion processes and in soil microbial process and lightning events. NO2 is an ozone-depleting substance produced primarily from the oxidation of nitrous oxide (N2O) (Crutzen, 1970; Johnston, 1971; Seinfeld and Pandis, 2006). NOx can suppress ozone depletion by converting reactive chlorine and hydrogen compounds into unreactive reservoir species (Murphy et al, 1993). NOx is in the form of NO2, which is oxidized by O3 to produce NO3, and NO3 is converted to N2O5 in the presence of NO2. N2O5 is produced at night and NO2 decreases during night
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