Powerful synthetic greenhouse gases such as hydrofluorocarbons, perfluorocarbons and sulfur fluoride that are emitted from various industrial processes. F-gases are sometimes used as substitutes for stratospheric ozone-depleting substances (eg, chlorofluorocarbons, hydrochlorofluorocarbons, and halons) and are often used in coolants, foams, fire extinguishers, solvents, pesticides, and aerosol propellants. These gases are emitted in small amounts compared to carbon dioxide (CO ₂ ), methane (CH ₄ ) or nitrous oxide (N ₂ O), but because they are strong greenhouse gases, they are sometimes referred to as gases with a high global warming potential. (High GWP gases).