We can define air with a high oxygen content, in which there are no pollutants such as particles, sulfur dioxide, nitrogen oxides, viruses, microbes and mites, as “Clean Air”

There are unwanted substances in polluted air at a level that will harm human health and other living beings. Particulate matter that we often don't notice, gases such as sulfur dioxide, nitrogen oxides, ozone and many other substances that are harmful to health pollute the air we breathe.