*2.3. OMI Data Retrieval*

Nitrogen dioxide (NO2) is a very important atmospheric gas in both the troposphere where it is a precursor to ozone production and in the stratosphere where it plays the main role in ozone chemistry (https://disc.gsfc.nasa.gov/datasets/OMNO2d\_003/summary, accessed on 25 March 2020). NO2 in the troposphere is produced in various combustion processes and lightning, which is an indicator of poor air quality [66]. NO2 product (OMNO2d) is a daily global Level-3 gridded data with a spatial resolution of 0.25 × 0.25◦ [67,68] which contains time-average tropospheric column (30% cloud screened) and area-average total column [31]. We further retrieved the dataset from optional tools (use smoothing, equidistant cylindrical projection system) with linear scaling and a maximum of 65 palettes were used for this study. In this process, we ignored negative values especially for the 10-day average of the NO2 total column map [31,69].
