*2.4.2 Ozone (O3)*

Ozone (O3) is an allotrope of oxygen and is much less stable than normal O2. It forms under the influence of ultraviolet light and during atmospheric electrical discharges (lightning). Even at low concentrations ozone causes damages to respiratory tracts of experimental animals and organic materials, such as latex and various types of plastic. The ozone's half-life depends on temperature, humidity and air circulation. In a closed room with running fan, ozone's half-life is about 24 hours [53]. That is, in a laboratory room, an instrument, like spectrophotometer or spectrophluorometer without special device for burning ozone (for example, instruments from Perkin Elmer), after several hours of work may create a concentration of ozone high enough to cause a headache and errors in experimental results due to accumulation of peroxides in water solutions.

#### *2.4.3 Nitrogen dioxide (• NO2)*

For the human's health it is important that in industrial areas with chemical factories and coal power stations the air may be polluted with nitrogen dioxide that may damage skin and respiratory organs. • NO2 induces oxidation, as well as cell's membrane proteins nitration. Nitrated biological products, for example, tyrosinecontaining proteins and nitrolipids are often found in the body. It is likely, that • NO2 has been involved in the formation of these products [54].
