The Ozone molecule is naturally observed at low concentrations throughout the Earth's atmosphere. The scientists consider the ozone in stratosphere (10 to 50 km above Earth's surface) as 'good', because its protects life on Earth from the sun's ultraviolet rays. However, they also point to the 'bad' ozone, that is the one observed in the troposphere by the human activities that lead to a concentration several times higher than the normal amount of ozone (may cause respiratory and vegetation damages). The release of Ozone by human activities is what causes it to accumulate in the lower atmospheric layers, being harmful for the living beings.