Classical is related to Fire. Fire is related to Ash. you are likely to find Ash in/at/on Air. you are likely to find Pollution in/at/on Air. 
Evidence is a synonym of Witness. Witness is related to Observer. 
Classical <--RelatedTo--> Fire <--RelatedTo--> Ash --AtLocation--> Air <--AtLocation-- Pollution 
Evidence <--Synonym--> Witness <--RelatedTo--> Observer 