Description of colours:
Blue and dark blue colour informs: air quality is very good, you can spend time outside without limit.
Green colour informs: sensitive people (children, elderly people) should limit physical activity near busy streets.
Yellow colour advices: don't go for walks near major roads and districts heated by coal.
Orange colour warns: only healthy people can practise sport outside, leave car at home.
Red colour alarms: if you have problem with health , you should stay at home. If you feel bad, you can go to doctor. Leave car at home and use public transport or bike.