Electrochemical sensor for the determination of nitrogen (II) oxide in air, the cell of which contains working and auxiliary electrodes and a reference electrode placed in the housing, separated by separators impregnated with an electrolyte solution. The cell is made in the form of a tablet, in which the electrodes and the separator are connected by layer-by-layer pressing, with the working electrode made of porous titanium activated with ruthenium (IV) oxide, the reference electrode is made of a mixture of conductive material stable in the electrolyte medium and manganese (IV) oxide, the auxiliary electrode is made of porous titanium activated with platinum, the separator is made of a mixture of polymeric binder and hydrophilizing additive, and an aqueous solution of 5-7 mol/kg perchlorate acid is used as an electrolyte.
