NO 2 observations over the western Pacific and Indian Ocean by MAX-DOAS on Kaiyo , a Japanese research vessel

Nitrogen dioxide (NO2) profile retrievals were performed by ship-borne Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) using a compact/low-power spectrometer on the Japanese research vessel Kaiyo during two ocean cruises around Japan and Japan–Bali (Indonesia)–Indian Ocean. DOAS analysis using a 425–450 nm fitting window revealed a clear land–ocean contrast in NO2 differential slant column densities (DSCDs) but poor fitting results and negative values, especially at low elevation angles at low latitudes (