Aerosols are fine solid or liquid particles suspended in a gas. Carbonaceous aerosols are fine, solid carbon particles suspended in the atmosphere. They result from burning fossil fuels, which are not completely consumed in the combustion process. Sometimes, these aerosols are referred to as "soot." They can affect the global climate, as well as causing problems for people who breathe the air: They are associated with allergies and respiratory diseases, as they interfere with breathing by clogging the air sacs in a person's lungs. These aerosols are also a major cause of pollution-related mortality.

Carbonaceous aerosols are made up of two parts: Organic carbon (OC), which scatters light, and black carbon (BC), which absorbs light. These particles can block radiation from the Sun and scatter light, so they can affect Earth's climate in several ways. They can scatter and absorb radiation from the Sun. They can reflect light back into space, increasing Earth's albedo directly, and they can also make clouds more reflective, increasing it indirectly. OC in particular is able to do this, offsetting the warming that greenhouse gases (GHGs) cause. Carbonaceous aerosols, particularly BC, can also heat the atmosphere by absorbing sunlight.

Carbonaceous aerosols can block light from reaching the Earth's surface. BC also does this, which can lead to cooling the Earth's surface. They can affect the amounts of trace gases in the atmosphere, which may affect warming or cooling of the atmosphere depending on which type of gas is affected. They can combine with each other and other particles to interact in different ways that lead to unusual, and sometimes perplexing, effects on the global climate.

Thus, carbonaceous aerosols can affect both the warming and cooling of the Earth and its atmosphere. Scientists are still trying to understand the complexities of how these aerosols affect global climate change, though some estimate that black carbon particles may be responsible for 15 to 30 percent of global warming.

Tihomir Novakov and his research group at Lawrence Berkeley National Laboratory have been leaders in performing significant research on carbonaceous aerosals since the 1970's, and it is mostly due to this work that these particles are now accepted as being common in the atmosphere. (Previously, scientists thought that fossil fuels burned completely and left no fine solid particles in the atmosphere.)

The effect that carbonaceous aerosols have on the environment can be influenced by the number of these particles contained in the total volume of air, the size of the particles, and the proportion of organic versus black carbon composing each particle. Studying aerosols can be difficult. Carbonaceous aerosols do not last long and do not mix in the same way in all areas across the Earth, which makes analyzing their effects difficult. The way these particles interact with water, particularly salt water, and over areas covered with snow and ice is not well understood and is a subject of scientific inquiry. Previous major studies, such as the Asian-Pacific Regional Aerosol Characterization Experiment (ACE-Asia) in 2001 and the Indian Ocean Experiment (INDOEX) in 1991, relied on large teams of scientists using aircraft, balloons, ships, and surface stations to help analyze these effects.

Carbonaceous aerosols can affect the hydrologic cycle by cutting down the amount of sunlight that is able to reach the ocean, affecting how quickly seawater evaporates into the air. They may also affect how clouds are formed. Both these actions can reduce the amount and frequency of rainfall. Carbonaceous aerosols can also affect plants by coating their leaves and affecting their ability to photosynthesize or use light to break down chemical compounds, thus also contributing to global climate change.

Bibliography:

1)         Gelencser, Andras. Carbonaceous Aerosol. Dordrecht, the Netherlands: Springer, 2004.

2)         Jacobson, Mark. "Strong Radiative Heating Due to the Mixing State of Black Carbon in Atmospheric Aerosols." Nature 409 (February 15, 2001): 695-697.

3)         Novakov, T. "The Role of Soot and Primary Oxidants in Atmospheric Chemistry." The Science of the Total Environment 36 (1984): 1-10.

4)         Ramanathan, V., and G. Carmichael. "Global and Regional Climate Changes Due to Black Carbon." Nature Geoscience 1 (2008): 221-227.

5)         Rosen, H., T. Novakov, and B. Bodhaine. "Soot in the Arctic." Atmospheric Environment 15 (1981): 1371-1374.

6)         Wolff, G. T., and R. L. Klimisch, eds. Particulate Carbon-Atmospheric Life Cycle. New York: Plenum, 1982.

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