The Sentinel-5P TROPOMI Near Real Time (NRT) Sulphur Dioxide SO2 1-Orbit L2 5.5km x 3.5km V2 (S5P_L2_SO2___HiR_NRT) at GES DISC is the near real time version of the offline S5P_L2_SO2___HiR data product. These data are typically available within three hours of measurement as required by the Land Atmosphere NRT Capability Earth Observing System (LANCE). These data are intended for a rapid turnaround assessment and are only archived for up to ten days. Users who require a longer data record, or wish to conduct rigorous analysis should use the offline version of this product S5P_L2_SO2___HiR.

The Copernicus Sentinel-5 Precursor (Sentinel-5P or S5P) satellite mission is one of the European Space Agency's (ESA) new mission family - Sentinels, and it is a joint initiative between the Kingdom of the Netherlands and the ESA. 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 SO2 from ultraviolet spectral measurements is the Differential Optical Absorption Spectroscopy (DOAS) method. The relevant information of absorption cross section, instrument characteristics, cloud cover, and geolocation are utilized to derive SO2 slant column density (SCD). A sensitive spectral window of 312 to 326 nm is set as the baseline for the slant column fit with another two spectral windows (325 to 335 nm, 360 to 390 nm) to account for the non-linear effects in those high column amount cases. The SCD is then corrected with the empirical offsets to the systematic biases. The air mass factor (AMF) Look-up table has been created with the LIDORT radiative transfer model. The outputs of the DOAS algorithm are SO2 vertical column density (VCD), SCD, AMF, the DOAS-type averaging kernels (AK), and error estimates. Data are stored in individual files, or granules, that contain one orbit of information. The data are stored in netCDF4 data format and files and complete files are ~100 MB.