Where is it found? Ozone (O3) is found in the troposphere and it is the result of the atmospheric reaction of a number of precursor pollutants, which come from both natural and anthropogenic sources. Precursor pollutants are originated by human activities and include hydrocarbons and nitrogen oxides. They are largely emitted by cars and other vehicles, fossil fuel power plants, oil refineries, the agriculture sector and a number of other industries. O3 is areactivegas thatexists in two layers oftheatmosphere: the stratosphere (upper layer) and the troposphere (at ground level and up to 15 km). Ozone, in the upper layer, is essential to protect the Earth from the sun’s ultraviolet rays. At lower levels, it is an important greenhouse gas and an air pollutant, which is harmful to human and ecosystem’s health. It is also the major component of urban smog. The O3 cartridge has a built-in electrochemical sensor responsive to NO2 and O3 concentrations. Hence, in order to measure accurately the O3 concentration, it is required to install in the same device the NO2 cartridge. The Kunak algorithm considers both concentrations allowing for accurate O3 measurements with no NO2 influence, even at high temperatures which are related to higher O3 concentration due to the solar radiation. Unit of measurement Measurement range (1) Resolution (2) Operating temp. range (3) Operating RH range (4) Recommended RH range (4) Operating life (5) Limit of Detection (LOD) (7) Repeatability (8) Typical Intra-model variability (14)