In the atmospheric air of many cities of the Russian Federation growth of the concentration of formaldehyde is noted recently. It is not always connected with a concrete source pollutant. Atmospheric air is the environment in which chemical reactions of the transformation of substances in others, under the influence of various factors, first of all, the climatic continuously proceed. Thus, at a certain air temperature methane is able to transform to formaldehyde, increasing its concentration. In work changes of the content of formaldehyde in atmospheric air of the ground of warehousing of rainfall of “Nothern” sewage SUE “Vodokanal-SPb” and the adjacent territory, depending on the temperature of atmospheric air and concentration of methane are considered.