The .xlsx files for NO2 in implementation/data/raw were downloaded from the Bavarian Ministry for Environment. The data is licensed under the CC BY 4.0 license.
The file implementation/data/LUF_merged.csv contains all data from Munich between 2010 and now in one CSV file.
The file implementation/data/raw/dwd_klima_flughafen.txt was downloaded from the German Weather Service (DWD). The data is available without any restrictions (DWD: "no restrictions except when stated", https://www.dwd.de/DE/leistungen/klimadatendeutschland/ueberblick.html?nn=16102&lsbId=526270).
In implementation/data/DWD_merged.csv this data has been cleaned up and reduced to the variables of concern.