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I have downloaded Sentinel 5P NO2 Tropospheric vertical column data through the Google earth engine (GEE) code editor platform. The datasets have negative values in micromol per square meter (μmol/m-2). after mapping the dataset and converting the data from micro mol per square meter (μmol/m-2) to Dobson Unit(DU), some areas show negative values of NO2 with a minimum starting from -0.035. So, I have a query on is the datasets are correct, which I have extracted through coding in GEE and what the negative Du value means, and what we can evaluate from the map having negative tropospheric vertical column NO2 DU value regions. I would appreciate your assistance in identifying my mistakes in the process.
I apologize for the delay in this reply, as we have considered various causes of negative values in the data retrieval.
Assuming the negative values aren't coming from fill values, they are not that uncommon, and can arise for a number of reasons. E.g. the atmosphere modelled is not a good representation of the actual atmosphere, or mathematical approximations for the geometry (ringing) -- this is more likely in profile measurement, though. An important point is that negative retrieved values -- even if unphysical -- need to be kept in any analysis, particularly averaging.