A trace gas is any type of gas that occurs in small concentrations, many of them in concentrations of one part per billion (ppb) or lower. Trace gases are often used when referring to gases within the atmosphere of Earth. In this context, trace gases make up less than 1% of all atmospheric gases. The noble gas argon (Ar) is the most common trace gas found in Earth's atmosphere. Other trace gases within the atmosphere include hydrogen (H), helium (He), neon (Ne), krypton (Kr), and xenon (Xe).
The most important trace gases found in Earth's atmosphere are the so-called greenhouse gases. These trace gases are called greenhouse gases because they help to keep Earth warm by absorbing light from the sun. Found in the troposphere, these gases include water vapor, ozone (O3), carbon dioxide (CO2), methane (CH4), sulfur dioxide (SO2), and nitrous oxide (N2O). The two most abundant greenhouse gases by volume are water vapor and carbon dioxide.
Historical Background and Scientific Foundations
Scientists have found that natural greenhouse gases keep the surface of Earth warmer when compared to its temperature if Earth did not have an atmosphere. However, over the past 150 years or so, human activities have introduced artificial greenhouse gases into the atmosphere, which are adding extra warmth to the surface of Earth—what is called the greenhouse effect.
An important natural trace gas with respect to the greenhouse effect is ozone. In the stratosphere, the ozone layer helps to screen out harmful ultraviolet radiation from the sun. Other naturally produced trace gases in the atmosphere come from natural phenomena such as forest fires, lightning bolts, and volcanic eruptions. Such gases include nitrous oxide and sulfur dioxide.
Humans have also increased these two gases in the atmosphere with the production of pollution from such activities as operating motorized vehicles and the combustion of fossil fuels within manufacturing facilities. Other trace gases introduced into the atmosphere by human processes include chlorofluorocarbons (CFCs), which damage the ozone layer.
Impacts and Issues
Naturally produced trace gases in Earth's atmosphere have played important roles in climate change for millennia. Research today has found that the reduction of trace gases is important for controlling global climate in the future. Thus, scientists are studying the relationship between trace gases, carbon dioxide, and global warming.
Carbon dioxide is widely considered the largest compound, which has been introduced into the atmosphere by human activities, to cause detrimental environmental affects on Earth. Studies to slow its emissions into the atmosphere are ongoing by scientists. Trace gases—what are also called non-carbon-dioxide gases— also need to be reduced, according to these scientific studies, in order to take positive steps toward a cleaner atmosphere.
Specifically, researchers have shown that reductions of trace gases may reduce the growth of global warming. They contend that emissions of carbon dioxide, which is the largest atmospheric pollutant, must be slowed. However, its decrease in emissions might be less than first thought if trace gases are also limited at the same time.
In fact, researchers at the National Aeronautics and Space Administration's Goddard Institute for Space Studies contend that global warming could be kept to a temperature increase of less than 1.8°F(1°C) per year when such action—reductions in the emissions of both carbon dioxide and non-carbon-dioxide gases (trace gases)—is performed. This combined reduction could help alleviate global climate concerns by preventing further degradation of coastlines around the world, reducing the melting of ice masses, increasing agricultural productivity, and improving the global environment.
WORDS TO KNOW
CHLOROFLUOROCARBONS: Members of the larger group of compounds termed halocarbons. All halocarbons contain carbon and halons (chlorine, fluorine, or bromine). When released into the atmosphere, CFCs and other halocarbons deplete the ozone layer and have high global warming potential.
NOBLE GAS: Elements of group 18 of the periodic table, including helium, neon, argon, krypton, xenon, and radon. These are called noble because they do not easily form chemical bonds with other elements (i.e., keep aloof, as nobles might be supposed to do).
OZONE LAYER: The layer of ozone that begins approximately 9.3 mi (15 km) above Earth and thins to an almost negligible amount at about 31 mi (50 km) and shields Earth from harmful ultraviolet radiation from the sun. The highest natural concentration of ozone (approximately 10 parts per million by volume) occurs in the stratosphere at approximately 15.5 mi (25 km) above Earth. The stratospheric ozone concentration changes throughout the year as stratospheric circulation changes with the seasons. Natural events such as volcanoes and solar flares can produce changes in ozone concentration, but man-made changes are of the greatest concern.
STRATOSPHERE: The region of Earth's atmosphere ranging between about 9 and 30 mi (15 and 50 km) above Earth's surface.
TROPOSPHERE: The lowest layer of Earth's atmosphere, ranging to an altitude of about 9 mi (15 km) above Earth's surface.
ULTRAVIOLET RADIATION: The energy range just beyond the violet end of the visible spectrum. Although ultraviolet radiation constitutes only about 5% of the total energy emitted from the sun, it is the major energy source for the stratosphere and mesosphere, playing a dominant role in both energy balance and chemical composition.
The Atmosphere, edited by R. F. Keeling. Boston: Elsevier, 2006.
Emissions of Atmospheric Trace Compounds, edited by Claire Granier, Paulo Artaxo, and Claire E. Reeves. Boston: Kluwer Academic Publishers, 2004.
Seinfeld, John H. Atmospheric Chemistry and Physics: From Air Pollution to Climate Change. Hoboken, NJ: John Wiley, 2006.
“Climate Change and Trace Gases.” Philosophical Transactions of the Royal Society, May 18,2007. <http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf> (accessed November 10, 2007).
“Trace Gases Are Key to Halting Global Warming.” Science Daily, February 9, 2001. <http://www.sciencedaily.com/releases/2004/11/041122100820.htm> (accessed November 10, 2007).
William Arthur Atkins