Emission is related to Pollution. you are likely to find Pollution in/at/on Sky. Sky is etymologically related to Hide. 
Interval is a type of Distance. Interval is related to Year. Year is related to Measure. 
Emission <--RelatedTo--> Pollution --AtLocation--> Sky --EtymologicallyRelatedTo--> Hide 
Distance <--IsA-- Interval <--RelatedTo--> Year <--RelatedTo--> Measure 