I think it is noticeable that before any aarti this shlok is recited before the start of aarti. my question is, is there any reason behind it and is it also happening from past.
Well, as said by The Destroyer and others it is not compulsory to recite this Sloka during Arati in all Pujas.You might have seen it being done during a Shiva Puja & which is quite ok. Because this Sloka is related to Shiva and not to Arati Mantras(also called Nirajana Mantras) in general.
The Karpura Gouram term (as said by the destroyer) refers to the camphor like white skin colour of Lord Shiva.Similar terms like "Tushardri Sankasha Gauram"(white as mountain snow) are elsewhere used with the same purpose.
In Vedic Pujas ,it is customary to recite few Mantras while offering the various Upcharas.
For Karpura (camphor)Arati(during all Pujas) we have the following general Mantra(to be uttered while offering Arati to any Deity).
Om Idam Havih Prajanam Me Astu DasaViram sarvaganam Swastaye|| Atamasani Prajasani Pasusani Loka Sanya Bhayasani||Agnim Prajam Bahulam Me Karotvannam Payo Reto Asmasu Dhatta
Kadali Garva Samvutam Karpuram tu Pradipitam|| Aaraartikamaham Kurve Pasya Me Barado Bhavo||
The first Mantra is from Yajur Veda.Also note that these Mantras changes with Vidhanas(like Sri Sukta Vidhana,Purusha Sukta Vidhana etc)
The Mantra that i have posted does not change with Deities(assuming the Vidhana is same) but some people do sing Stutis of Gods while doing Arati.These Stutis of course varies from Deity to Deity.