The concentration of water vapor decreases drastically with altitude. The upper troposphere has considerably less water vapor than air near the surface, the stratosphere and mesosphere have almost no water vapor, and the thermosphere contains none at all. Air also contains tiny solid particles called aerosols , such as dust, sea salt, and ash from erupting volcanoes or forest fires. Many of these particles are so small that they are microscopic. Others are large enough to see. Aerosols affect climate by helping clouds form and shading the planet by scattering or absorbing sunlight.
In the last century, manufacturing and widespread use of combustion engines have increased the number of aerosols in the atmosphere as particulate matter spews from smokestacks and exhaust pipes. Burning wood and other materials also add particles to the air. Like everything on Earth, the air is made of chemicals. Many of these chemical reactions help maintain healthy natural environments and are vital for plants and animals.
Nitrogen gas in the atmosphere does almost nothing, but nitrogen elsewhere on Earth is essential for life. Through the nitrogen cycle , nitrogen makes its way into soil and water, binds with other elements, and can be used by living things.
Oxygen from the atmosphere causes oxidation reactions that help break down matter and release nutrients into soils, and is used by humans and animals in cellular respiration. Atmospheric chemistry in the troposphere is also influenced by human-made chemicals that can negatively impact human health and the environment.
For example:. The table below lists the major gas components and their role in the atmosphere. However, living things cannot use N 2 in its gaseous form in the atmosphere. Nitrogen gas found in air pockets within soil is converted into a form usable by plants through a process called nitrogen fixation.
Nitrogen-fixing organisms include certain types of bacteria and other micro-organisms that live on the roots of legumes such as soybeans, alfalfa and red clover. The micro-organisms convert N 2 into other compounds such as ammonium and nitrate, which are taken up by plant roots. Consumers eat the plants and later deposit nitrogen compounds back into the soil through elimination or decomposition.
Plants also return nitrogen to the soil when they decompose. The nitrogen-fixing micro-organisms in soil break down these compounds, and the nitrogen cycle continues. Because nitrogen can be highly reactive at high temperatures, nitrogen oxide compounds form when fuel is burned.
One of these compounds, nitrogen dioxide NO 2 , is a byproduct of combustion and is present in emissions from automobiles and factories. In gaseous form, NO 2 is a respiratory irritant. In the presence of water in the atmosphere, it can react to form acid rain. She worked as a researcher and analyst in the biotech industry and a science editor for an educational publishing company prior to her career as a freelance writer and editor.
Alissa enjoys writing about life science and medical topics, as well as science activities for children. When there are too many particles in the air, it can be difficult for plants and animals to breathe. People need to breathe, and so do lots of other animals—and plants!
Breathing is part of a process called respiration. During respiration, a living thing takes in oxygen from the air and gives out carbon dioxide. This process gives animals and plants the energy to eat, grow, and live life! When humans and animals breathe, we give off an odorless gas called carbon dioxide, or CO 2. Plants use this gas, along with sunlight, to make food—a process called photosynthesis. In this process, plants give off oxygen, too! However, large amounts of CO 2 are also produced when cars and power plants burn coal, oil, and gasoline.
CO 2 is also the most important contributor to human-caused global warming. Relative humidity is the amount of water that the air can hold before it rains. Humidity in the air is measured with an instrument called a psychrometer.
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