A measuring device (10) and a measuring method measure a concentration of gaseous and/or aerosol components of a gas mixture. A reaction carrier (14) has a flow channel (42) defining a reaction chamber (46) with an optically detectable reaction material (48) to react with at least one component or with a reaction product of the component. The measuring device (12) includes a gas delivery unit (2) and detection unit (3) having a lighting device (37) for lighting the reaction chamber (46). An optical sensor (38) detects the reaction. An evaluation unit (4) evaluates data of the optical sensor (38) to determines a concentration. The gas delivery unit (2) includes a gas delivering device (28) delivering the gas mixture through the gas outlet channel (18) and a control/regulation unit (31) which controls/regulates a flow of the gas mixture through the flow channel (42) depending on at least one reaction speed parameter.