A system for I) collecting nitrous oxide in air exhaled by an individual inhaling nitrous oxide via a face mask arrangement (= face mask) having an outlet OL mask for exhalation, and II) delivering the nitrous oxide collected in to an inlet port IP app of an apparatus for further processing of nitrous oxide, wherein the system comprises a pool of one or more mutually replaceable through-flow adsorption units, each of which comprises a nitrous oxide reversible adsorbent placed in a through-flow chamber and has: i) an inlet port IP ads for inlet of exhalation air (adsorption flow), ii) an outlet port OP ads for discharging gas processed in the chamber to a waste recipient, iii) an inlet port IP des for inlet of a desorbing gas (desorption flow), and iv) an outlet port OP des for discharging desorbing gas from the adsorbent, together with A) a docking arrangement DA ads which is associated with adsorption of nitrous oxide and comprises a connection C1 ads for connecting the outlet port OL mask to the inlet port IP ads, and B) a docking arrangement DA des which is associated with desorption of nitrous oxide and comprises a connection C2 des for connecting the outlet port OP des to the inlet port IP app characterized in that the system is associated with a measuring arrangement which comprises one or more sensors (208a,b,308a,b,c) which are based on measuring the amount of nitrous oxide on the adsorbent during and/or after adsorption, and in that A) the adsorbent in the adsorption units is selected amongst adsorbents for which the adsorption of nitrous oxide is exothermic developing measurable changes in temperature where adsorption is ongoing indicating the advancing front of adsorption, and B) one or more temperature sensitive sensors (308a,b,c) which a) are capable of measuring changes in temperature in the adsorbent caused by adsorption of nitrous oxide, and b) are placed at different predetermined longitudinal positions between an inlet end and an outlet end of the adsorbent. I) collecting nitrous oxide in air exhaled by an individual inhaling nitrous oxide via a face mask arrangement (= face mask) having an outlet OL mask for exhalation, and II) delivering the nitrous oxide collected in to an inlet port IP app of an apparatus for further processing of nitrous oxide, i) an inlet port IP ads for inlet of exhalation air (adsorption flow), ii) an outlet port OP ads for discharging gas processed in the chamber to a waste recipient, iii) an inlet port IP des for inlet of a desorbing gas (desorption flow), and iv) an outlet port OP des for discharging desorbing gas from the adsorbent, together with A) a docking arrangement DA ads which is associated with adsorption of nitrous oxide and comprises a connection C1 ads for connecting the outlet port OL mask to the inlet port IP ads, and B) a docking arrangement DA des which is associated with desorption of nitrous oxide and comprises a connection C2 des for connecting the outlet port OP des to the inlet port IP app characterized in that the system is associated with a measuring arrangement which comprises one or more sensors (208a,b,308a,b,c) which are based on measuring the amount of nitrous oxide on the adsorbent during and/or after adsorption, and in that A) the adsorbent in the adsorption units is selected amongst adsorbents for which the adsorption of nitrous oxide is exothermic developing measurable changes in temperature where adsorption is ongoing indicating the advancing front of adsorption, and B) one or more temperature sensitive sensors (308a,b,c) which a) are capable of measuring changes in temperature in the adsorbent caused by adsorption of nitrous oxide, and b) are placed at different predetermined longitudinal positions between an inlet end and an outlet end of the adsorbent. A) a docking arrangement DA ads which is associated with adsorption of nitrous oxide and comprises a connection C1 ads for connecting the outlet port OL mask to the inlet port IP ads, and B) a docking arrangement DA des which is associated with desorption of nitrous oxide and comprises a connection C2 des for connecting the outlet port OP des to the inlet port IP app A) the adsorbent in the adsorption units is selected amongst adsorbents for which the adsorption of nitrous oxide is exothermic developing measurable changes in temperature where adsorption is ongoing indicating the advancing front of adsorption, and B) one or more temperature sensitive sensors (308a,b,c) which a) are capable of measuring changes in temperature in the adsorbent caused by adsorption of nitrous oxide, and b) are placed at different predetermined longitudinal positions between an inlet end and an outlet end of the adsorbent. a) are capable of measuring changes in temperature in the adsorbent caused by adsorption of nitrous oxide, and b) are placed at different predetermined longitudinal positions between an inlet end and an outlet end of the adsorbent.