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Atmospheric Aerosols - Introduction and Overview
Effects of Atmospheric Aerosols
Health
According to the American Academy of Allergy, Asthma and Immunology, approximately 20 million Americans have asthma, and the prevalence of asthma has increased dramatically in recent decades. The cause of this increase is not well understood, but aerosols, both natural and anthropogenic, create serious challenges for people with asthma or other lung problems, and children growing up in heavily polluted cities have lowered lung function. Asthma costs Americans billions of dollars every year. Very fine particulates (2.5 micrometers or less in diameter) can penetrate deep into the lungs. The finest particles can also leave the lungs to enter the bloodstream and affect other parts of the body, especially as carcinogens.
Ozone Layer
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The hole in the ozone layer above Antarctica
Image credit Fritz Hasler and Hal Pierce, Laboratory for Atmospheres, NASA Goddard Space Flight Center. |
High up in the atmosphere is a layer called the stratosphere. Part of the stratosphere is the ozone layer, which absorbs ultraviolet B wavelengths. UVB is known to cause skin cancer; therefore a healthy ozone layer is very important to human health.
Many synthetic products once contained chlorine compounds called chlorofluorocarbons (CFCs) that can end up in the stratosphere or even higher. Some other ozone depleting substances, including methyl bromide and methyl chloroform, are still used as insecticides and industrial solvents. Chlorine or bromine from ozone depleting substances reacts with ozone in the stratosphere, diminishing the ozone layer. Aerosol particles that are able to drift all the way up to the stratosphere are thought to provide a surface on which chlorine can react with ozone more rapidly. In other words, atmospheric aerosols can make chlorine more effective at destroying ozone.
Global Climate Change
Aerosols are a major uncertainty in studies of global climate change. They can have both direct and indirect effects on climate, and depending on what effects predominate, may either contribute to global cooling or global warming. The emission of sulfur dioxide from the burning of coal and oil are of particular concern, because not only does some of this end up as acid rain (another serious environmental problem), but a large fraction becomes sulfate aerosols.
The direct effects of aerosols are the scattering (which causes cooling) and absorption (which causes warming) of sunlight. High concentrations of aerosols in certain localities may cause local warming, which can alter air currents. Atmospheric aerosols can also affect climate indirectly by acting as “cloud condensation nuclei,” which make the liquid droplets in clouds smaller. Clouds with smaller droplets have longer lifetimes and reflect more sunlight. Smoke stacks from cruise ships eject aerosols, and satellites can chart ships' progress across the ocean because they leave an artificial cloud trail behind them.
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