Ozone depletion Ozone depletion Ozone depletion describes two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone around Earth's polar regions. The latter phenomenon is referred to as the ozone hole. There are also springtime polar tropospheric ozone depletion events in addition to these stratospheric events. The main cause of ozone depletion and the ozone hole is manufactured chemicals, especially manufactured halocarbon refrigerants, solvents, propellants and foam-blowing agents (chlorofluorocarbons (CFCs), HCFCs, halons), referred to as ozone-depleting
Ozone Action Day Ozone Action Day An Ozone Action Day, which can be declared by a local municipality, country or state, is observed at certain times during the summer months, when weather conditions (such as heat, humidity, and air stagnation) run the risk of causing health problems. Ozone Action Days, alternately called an "Ozone Alert" or a "Clean Air Alert", primarily center in the midwestern portion of the United States; particularly in well-urbanized areas such as Chicago, Cleveland, Detroit, and Indianapolis. Although the ozone found at the Earth's surface is the same chemical species as that found in the ozone layer, they have