Vegetables are alive, they respire and they interact with the atmosphere around them. Normal air contains approximately 400ppm carbon dioxide (CO2), or 0.04%. Air also contains approximately 21% oxygen (O2), with 78% Nitrogen (N2) forming the bulk of the remainder, along with traces of water vapour and other gases — argon, helium, hydrogen, etc. Manipulating the gas concentrations in the atmosphere around fresh products can maintain quality and extend storage life.
Vegetables generate many volatile compounds, of which ethylene is the most important. Ethylene can have many different effects, most of which are undesirable for vegetable storage life and quality.