• Question: Why is the air clear

    Asked by Orlamccrea to James on 14 Nov 2014.
    • Photo: James Sullivan

      James Sullivan answered on 14 Nov 2014:

      Hi Orla,
      lovely question

      For something to have a colour it has to absorb visible light. There are a range of colours in visible light (think of a rainbow). The light reflected from it then (that is not absorbed) is what we see and perceive as colour – so green leaves absorb red and blue light and we perceive what’s reflected as green.

      The air is mostly nitrogen (N2) and oxygen (O2) and these gases do not absorb visible light. therefore the air is clear.

      In polluted air sometimes you can have NO2 – nitrogen dioxide. This does absorb visible light – and appears as a brown gas – this is why polluted air sometimes looks brown.

      I hope this is clear for you.