A refrigerant is considered a Class I substance if it has a significant potential to affect which atmospheric layer?

A refrigerant is classified as a Class I substance if it has a significant potential to deplete the ozone layer, which is located in the stratosphere. The stratospheric ozone layer is crucial for absorbing the majority of the sun's harmful ultraviolet (UV) radiation, thereby protecting life on Earth from damage caused by excessive exposure to UV rays.

Class I substances typically include certain chlorofluorocarbons (CFCs) and halons, which release chlorine or bromine when they break down in the stratosphere. These released chemicals catalyze the destruction of ozone molecules, leading to thinning of the ozone layer and an increase in harmful UV radiation reaching the Earth's surface.

The other atmospheric layers—troposphere, mesosphere, and thermosphere—do not play a direct role in ozone depletion associated with refrigerants. While pollutants can have impacts in these layers, it is the stratosphere specifically that is concerned with the protection and maintenance of the ozone layer. This classification is critical in environmental regulations aimed at protecting the ozone layer and minimizing the impact of chemical substances on ecological health.