The purpose of this study was to examine possible treatments of combustion gas emissions, especially nitrogen monoxide, discharged by installations or equipment such as road tunnels, with very small amounts of pollutants (in the order of 10 mg m(-3)) and very large volumic flux (many thousands of m(3) h(-1)). After a feasibility study, we have shown the necessity to proceed with a preliminary step of pollutant concentration or oxidation in order to obtain an effective purification. We have developed two ways for treatment of nitrogen oxides (NOx), consisting of coupling physical, chemical and/or biological processes. In this paper,we present and discuss results regarding the second case, which consists of a nitrogen monoxide (NO) pre-concentration onto activated carbon (Pica NC. 60), followed by a thermal desorption of NOx and a biological treatment of the desorbed gas.