Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases, as from a fireplace, oven, furnace, boiler or steam generator. It often refers to the exhaust gas of combustion at power plants. Technology is available to remove pollutants from flue gas at power plants.
Combustion of fossil fuels is a common source of flue gas. They are usually combusted with ambient air, with the largest part of the flue gas from most fossil-fuel combustion being nitrogen, carbon dioxide, and water vapor.