An atmospheric gas burner assembly comprises a burner tube defining a multiplicity of gas outlet ports and an element reducing the flame temperature and, hence, the emission of oxides of nitrogen disposed above the burner tube in the flame area. To optimize the reduction of NO.sub.x emission without affecting permitted CO values and to render the values of reduction in NO.sub.x emissions largely independent of the geometry of the surrounding combustion chamber so as to obtain reproducible emission reduction values, the reducing element is constituted by a multiplicity of fins confining the flames in shafts extending therebetween, the fins extending perpendicularly above the tube and being distributed along the tube.