A cassette for conversion of nitrogen dioxide to nitric oxide comprising: a sealed housing, a first cartridge capable of converting nitrogen dioxide gas to nitric oxide within the sealed housing, the first cartridge comprising an inlet, a diverter, a body, an outlet, and a porous solid matrix including a reducing agent, the porous solid matrix being positioned within the first cartridge such that there is a space between the body of the first cartridge and the porous solid matrix, wherein the porous solid matrix includes an open passage parallel to the length of the body of the first cartridge, a second cartridge capable of converting nitrogen dioxide gas to nitric oxide, wherein an outlet of the first cartridge and an inlet of the second cartridge is connected, the second cartridge comprising an inlet, a diverter, a body, an outlet, and a porous solid matrix including a reducing agent, the porous solid matrix being positioned within the second cartridge such that there is a space between the body of the second cartridge and the porous solid matrix, wherein the porous solid matrix includes an open passage parallel to the length of the body of the second cartridge; and an inerting chamber including an inerting material. a sealed housing, a first cartridge capable of converting nitrogen dioxide gas to nitric oxide within the sealed housing, the first cartridge comprising an inlet, a diverter, a body, an outlet, and a porous solid matrix including a reducing agent, the porous solid matrix being positioned within the first cartridge such that there is a space between the body of the first cartridge and the porous solid matrix, wherein the porous solid matrix includes an open passage parallel to the length of the body of the first cartridge, the first cartridge comprising an inlet, a diverter, a body, an outlet, and a porous solid matrix including a reducing agent, the porous solid matrix being positioned within the first cartridge such that there is a space between the body of the first cartridge and the porous solid matrix, wherein the porous solid matrix includes an open passage parallel to the length of the body of the first cartridge, a second cartridge capable of converting nitrogen dioxide gas to nitric oxide, wherein an outlet of the first cartridge and an inlet of the second cartridge is connected, the second cartridge comprising an inlet, a diverter, a body, an outlet, and a porous solid matrix including a reducing agent, the porous solid matrix being positioned within the second cartridge such that there is a space between the body of the second cartridge and the porous solid matrix, wherein the porous solid matrix includes an open passage parallel to the length of the body of the second cartridge; and the second cartridge comprising an inlet, a diverter, a body, an outlet, and a porous solid matrix including a reducing agent, the porous solid matrix being positioned within the second cartridge such that there is a space between the body of the second cartridge and the porous solid matrix, wherein the porous solid matrix includes an open passage parallel to the length of the body of the second cartridge; and an inerting chamber including an inerting material.