The invention relates to a reducing agent metering system, and to a method for controlling the injection of a reducing agent into the exhaust gas flow (9) of a turbocharged internal combustion engine for selective catalytic reduction, wherein the metering system can be connected to a reducing agent tank (1), from which reducing agent can be removed, wherein the metering system comprises at least one nozzle (5) through which the reducing agent can be injected by means of compressed air into the exhaust gas flow (9), wherein at least one part of the compressed air is taken from a charger of the internal combustion engine, wherein the compressed air supply (6) comprises an electric air pump (7) for generating compressed air, and comprises a bypass (19) in parallel with the air pump (7), so that the charge air of the turbocharger flows over or can flow over the air pump (7).