5. Usage scenarios
1. You are interested in all stations of one country
https://toar-data.fz-juelich.de/api/v2/stationmeta/?country=DE provides all stations from Germany. The country must be specified with its ISO-3166 ALPHA-2 code (DE -> Germany).
2. You are interested in time series data for variables ozone and pm1 of a specific region
https://toar-data.fz-juelich.de/api/v2/variables/o3 and https://toar-data.fz-juelich.de/api/v2/variables/pm1 will get you the variable id for ozone (5) and pm1 (4).
https://toar-data.fz-juelich.de/api/v2/search/?bounding_box=49,7,50,8&variable_id=5,4 will get you all the time series within an area between 49°N 7°E and 50°N 8°E that record ozone or pm1.