Sentinel-5P TROPOMI Tropospheric Formaldehyde HCHO 1-Orbit L2 5.5km x 3.5km V2 (S5P_L2__HCHO___HiR)

The sole payload on Sentinel-5P is the TROPOspheric Monitoring Instrument (TROPOMI), which is a nadir-viewing 108 degree Field-of-View push-broom grating hyperspectral spectrometer, covering the wavelength of ultraviolet-visible (UV-VIS, 270nm to 495nm), near infrared (NIR, 675nm to 775nm), and shortwave infrared (SWIR, 2305nm-2385nm). Sentinel-5P is the first of the Atmospheric Composition Sentinels and is expected to provide measurements of ozone, NO2, SO2, CH4, CO, formaldehyde, aerosols and cloud at high spatial, temporal and spectral resolutions.

The retrieval algorithm for Sentinel-5P TROPOMI HCHO from ultraviolet spectral measurements is the Differential Optical Absorption Spectroscopy (DOAS) method. The relevant information of absorption cross section, instrument characteristics, cloud cover as well as aerosol index are utilized to derive HCHO slant column density (SCD). The air mass factor (AMF) Look-up table has been created with the VLIDORT 2.6 radiative transfer model at the wavelength of 340 nm, and the AMF is used to compute the total column averaging kernels (AK).

The background normalization of the slant columns is essential for weak absorbent like formaldehyde to compensate for possible systematic offsets. The main outputs of the DOAS algorithm are the vertical column density (VCD), SCD, AMF, uncertainty, AK, and quality flags.