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When you inhale, you are taking in many other gases besides the oxygen required by your body. Are these other gases important? What roles do they play in your body or in the atmosphere?

An important atmospheric gas is carbon dioxide (CO2). CO2 is a greenhouse gas. This means that it plays a direct role in keeping Earth's atmosphere warm enough to support life by regulating our planet's energy balance. You will learn how this regulation occurs later in the lesson.

Other greenhouse gases include water vapor (H2O), methane (CH4), ozone (O3), nitrous oxide (N2O), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs). Throughout our planet's history, greenhouse gases have regulated Earth's climate, helping to maintain temperatures supportive of life. However, as the concentrations of these gases increase, the temperature of the Earth and other planetary parameters are also affected. This is the primary concern regarding anthropogenic greenhouse gas emissions.

Ozone also plays a vital role in Earth’s atmosphere. While tropospheric ozone acts as a greenhouse gas, stratospheric ozone can be can be found higher up in the atmosphere, where it reacts with ultraviolet (UV) light. This reaction prevents the radiation from reaching the Earth and harming living organisms, including humans.

Nitrogen is an essential element for life, especially for the structure of plant and animal proteins. Although molecular nitrogen, N2, is the most abundant gas in the atmosphere, it is very stable and converting it to compounds that plants and animals can use is difficult. Lightning bolts and nitrogen fixing bacteria in soils are the main natural processes that carry out this conversion. Humans have devised ways to carry out nitrogen conversions, especially to produce fertilizers that have dramatically altered agriculture and natural nitrogen cycles.

The most abundant gases in Earth’s atmosphere—N2 and O2—are not greenhouse gases. These gases cannot increase the temperature of Earth’s atmosphere on their own, although they do play an indirect role by participating in collisional de-excitation.

Why Should We Care

Atmospheric gases play many important roles on Earth. These include the role of oxygen in sustaining life on Earth, the role of greenhouse gases in making Earth's climate suitable for life and the role of stratospheric ozone in providing protection from harmful ultraviolet radiation. Changes in the concentrations of atmospheric gases will affect the entire planet. For instance, changes in the concentration of greenhouse gases alter the temperature of our planet and ultimately impact Earth's climate.