The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Describe the composition of air (considering both its gases and its aerosols). Why are trace gases important? (A)

In order to describe the composition of air, it's important to identify its main components. The atmosphere consists primarily of gases, with trace amounts of aerosols and water vapor. Here are the most abundant gases found in the air along with their relative proportions by volume: 1. Nitrogen (N2) - about 78% 2. Oxygen (O2) - about 21% 3. Argon (Ar) - 0.93% 4. Carbon dioxide (CO2) - 0.040% 5. Neon, helium, krypton, and other noble gases - trace amounts Aside from these gases, air also contains tiny solid and liquid particles called aerosols. Some examples of aerosols include dust, pollen, sea salt, and smoke particles.

Trace gases are those that are present in very small amounts in the atmosphere. Although trace gases make up only a small fraction of the air, they are important because they can have a significant impact on various environmental processes. Some examples of trace gases include: 1. Methane (CH4) - a greenhouse gas that contributes to global warming 2. Ozone (O3) - an important contributor to the Earth's ozone layer which helps to protect us from harmful ultraviolet radiation 3. Sulfur dioxide (SO2) - a gas emitted from volcanic eruptions and some human activities which can lead to the formation of acid rain and play a role in climate 4. Water vapor (H2O) - although not usually considered a trace gas due to its higher relative abundance, water vapor is important for the Earth's climate and weather processes

Trace gases are important for several reasons. Firstly, some of them act as greenhouse gases, which help to trap heat in the Earth's atmosphere and regulate the planet's temperature. Additionally, trace gases can influence the Earth's climate and weather patterns, as well as contribute to a variety of environmental phenomena like the ozone layer and air quality. Certain trace gases are also used by plants and animals to carry out essential biological processes. Overall, despite their small quantities in the atmosphere, trace gases play a crucial role in maintaining the balance of our environment and supporting the survival of living organisms on Earth.