measuring units for Gas ...
Is it correct to measure NO2, SO2 etc. in m2 and not in m3 ?
There is only SO2 which is expressed in kg/m2. To get information about layer data click the small i in right bottom corner of screen.
For SO2 it is said that The variable presented here is the vertically integrated amount of sulphur dioxide from the ground and up to the top of the atmosphere. It is expressed in kg/m2.
So it is the quantity in a column from ground to top of atmosphere with a 1 square meter base. In this case this layer is not the gaz concentration near the soil. Reason why there is a plume of big quantity of SO2 over Mediterranean sea due to Etna volcano eruption, but not near the surface as shown by Air quality stations.