NOVELTY - A system (S1) comprises N-functionalized imidazole, which is non-ionic under neutral conditions.    USE - As system for reducing volatile compounds selected from carbon dioxide, hydrogen sulfide, sulfur dioxide, nitrogen oxide, nitrogen dioxide, carbonyl sulfide and/or carbon disulfide from a stream (where the stream is a gas stream or a liquid stream, and the gas stream is a natural gas stream or a flue gas stream) (claimed); for capture of volatile compounds in industrial and commercial natural gas production and power generation industries; also for reducing carbon monoxide, mercaptans, water, oxygen, hydrogen, nitrogen, and 1-8C hydrocarbons (e.g. methane and propane) from stream.    ADVANTAGE - The system is substantially free from volatile compounds. The N-functionalized imidazole and amine have multiple desired properties (e.g. low viscosity, low volatility, high carbon dioxide capacity). The viscosity of the N-functionalized imidazole is less than 10 cP at 24 degrees C, and the system containing the imidazole or blend of imidazole and amine effectively reduces the volatile compounds from gas streams and liquid streams; and allows sweetening a natural gas feed stream. The system allows removal of at least 10% (preferably 80%, especially 100%) carbon dioxide from stream as compared to a standard or a control system, which allows capture of volatile compounds in industrial and commercial natural gas production and power generation industries.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) reducing carbon dioxide from a stream involving contacting the stream with a system comprising N-functionalized imidazole and an amine, where the N-functionalized imidazole is non-ionic under neutral conditions; and    (2) sweetening (M1) a natural gas feed stream involving contacting the natural gas feed stream with a system (S1) comprising N-functionalized imidazole, where the N-functionalized imidazole is non-ionic under neutral conditions, to form a purified natural gas feed stream and a gas-rich system, and separating the purified natural gas feed stream from the gas-rich system.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the gas solubility apparatus.