Peroxyacetil Nitrate (PAN) in urban atmosphere: levels and behavior

During the high-pressure period the O x variable shows minimum values below the ozone background and maximum daytime values which can easily exceed this value (maximum O x values range between 120-160 ppb). The presence of intense radical activity is confirmed by the variation of PAN concentrations (maximum PAN values range between 20-30 ppb). PAN is the only member of nitrogenous compounds produced by photochemical processes, which has very low natural background concentrations so it is the specific indicator of anthropogenic photochemical air pollution.