Gas sensor, comprising - a surface tunnel emitter with an electron emitter structure, wherein the electron emitter structure comprises - an atmosphere-stable electron emission layer composed of a mixture of metals, wherein the atmosphere-stable electron emission layer comprises a first side and a second side; and - an electron acceleration structure on the first side of the electron emission layer with at least one electrode electrically insulated from the electron acceleration structure to form an acceleration path which is configured to allow electrons released from the electron emission layer to be accelerated in a targeted manner upon generation of a controllable electric field, wherein the acceleration path has a length l in the range from 10 nm to 1 μm, and wherein the surface tunnel emitter comprises an insulating layer arranged on the second side of the electron emission layer, which has a layer thickness of between 0.5 nm and 6 nm, and a metal layer arranged on a side facing away from the electron emission layer on the insulating layer, which has a layer thickness of between 0.5 nm and 6 nm, wherein both the electron emission layer and the insulating layer have layer thicknesses that can be tunnelled through, - an ion detection device; and - a pressure reduction container, in which the surface tunnel emitter is arranged, during operation of the gas sensor, the pressure in the pressure reduction container is reduced relative to the ambient pressure. - a surface tunnel emitter with an electron emitter structure, wherein the electron emitter structure comprises - an atmosphere-stable electron emission layer composed of a mixture of metals, wherein the atmosphere-stable electron emission layer comprises a first side and a second side; and - an electron acceleration structure on the first side of the electron emission layer with at least one electrode electrically insulated from the electron acceleration structure to form an acceleration path which is configured to allow electrons released from the electron emission layer to be accelerated in a targeted manner upon generation of a controllable electric field, wherein the acceleration path has a length l in the range from 10 nm to 1 μm, and wherein the surface tunnel emitter comprises an insulating layer arranged on the second side of the electron emission layer, which has a layer thickness of between 0.5 nm and 6 nm, and a metal layer arranged on a side facing away from the electron emission layer on the insulating layer, which has a layer thickness of between 0.5 nm and 6 nm, wherein both the electron emission layer and the insulating layer have layer thicknesses that can be tunnelled through, - an atmosphere-stable electron emission layer composed of a mixture of metals, wherein the atmosphere-stable electron emission layer comprises a first side and a second side; and - an electron acceleration structure on the first side of the electron emission layer with at least one electrode electrically insulated from the electron acceleration structure to form an acceleration path which is configured to allow electrons released from the electron emission layer to be accelerated in a targeted manner upon generation of a controllable electric field, wherein the acceleration path has a length l in the range from 10 nm to 1 μm, - an ion detection device; and - a pressure reduction container, in which the surface tunnel emitter is arranged,