Heat exchanger of an air-conditioning system of a cabin of a transport vehicle, comprising: a primary circuit supplied by a first air flow, a secondary circuit supplied by a second air flow, a casing defining an air-circulation enclosure, a primary circuit inlet box allowing entry into said air-circulation enclosure, and a primary circuit outlet box allowing exit from the air-circulation enclosure, characterized in that said inlet box is mounted removably on said casing, and in that it houses a three-dimensional structure forming a catalytic and/or adsorbent support for treating the air of said primary circuit, and a means for distributing said first air flow into said heat-exchange matrix.