CO 2 cannot be further oxidized. Plants breath CO 2 in the daylight, utilizing the carbon in the molecule to build their bodies while discharging oxygen back for people to breath. It is high levels of oxygen which make air fresh, along with low but measurable levels of ozone, very little dust, and no oxidizable chemicals . It feels so good to take a deep breath. Lightning storms are more frequent in mountains where during sunny days UV radiation from the sun also combines a small portion of oxygen into ozone.
Ozone is a disinfectant .
This time of year brings in cloud cover which limits UV radiation and therefore reduces the natural production of ozone. As a result, airborne bacteria and viruses get around much easier. When there is a surplus of Ozone in the air, it will kill all bacteria, viruses and mould. Ozone in natural settings is around 0.02 ppm, but it can be as high as 0.10 ppm. At this level it is capable of keeping pathogens in check and yet is not harmful to higher life forms such as fish, birds, animals or man.