Credits

Recirculate Vehicle Air by Lloyd Humphreys from the Noun Project (https://thenounproject.com/Lloyd/collection/automotive/?i=95600)
dirt by Shawn Erdely from the Noun Project (https://thenounproject.com/term/dirt/113123/)
breeze by Anusha Narvekar from the Noun Project (https://thenounproject.com/anusha.narvekar/collection/weather/?i=125453)
Cooling Tower by Florent from the Noun Project (https://thenounproject.com/floicons/uploads/?i=202484)
growth by Roberto Chiaveri from the Noun Project (https://thenounproject.com/term/growth/203582/)
Ecology Icons (http://www.webdesignerdepot.com/2013/12/free-download-vector-ecology-icons/)