Comment on Kazemi Garajeh et al. Monitoring Trends of CO, NO2, SO2, and O3 Pollutants Using Time-Series Sentinel-5 Images Based on Google Earth Engine. Pollutants 2023, 3, 255–279

Monitoring air quality is crucial on a global level. However, it is important to acknowledge the limitations of satellite-derived data in measuring gas concentrations. The Sentinel-5 satellite estimates pollutant density within an atmospheric column by measuring both the reflected solar radiation and the emitted radiation from the top of the Earth’s atmosphere. In other words, it assesses the presence of pollutants within the atmospheric column, but it cannot generate a method to isolate the amount of pollutants near the Earth’s surface from the total measured by the satellite. The authors completely ignored the methodology for converting the pollutant’s gas density within the atmospheric column into parts per million. In this commentary, we aim to clarify that it is neither practically nor operationally feasible to perform what the authors claimed as an evaluation of the accuracy of Sentinel-5p measurements from the ground stations they mentioned.