Sulfate aerosols are mixtures of solid or liquid particles that include sulfuric acid. The particles are a few microns in size. Most sulfate aerosols exist as a haze in the tropo-sphere, the layer of the atmosphere that goes from the ground up to about 9 miles (15 km). These sulfate
aerosols start as emissions from burning fossil fuels and last only a few weeks. Tropospheric sulfate aerosols act as condensation nuclei that cause cloud cover to increase. They are also a source of acid rain.
A severe volcanic eruption, such as Mount Pinatubo in the Philippines in June 1991, can send natural sulfate aerosols up into the stratosphere, the layer in the atmosphere above the troposphere. When sulfate aerosols reach the stratosphere, they can remain there for months and affect global temperatures for as much as a year.
Historical Background and Scientific Foundations
Sulfur dioxide in reactions with other atmospheric gases is converted to sulfur trioxide, which combines with water to form sulfuric acid. The Mount Pinatubo volcano blasted millions of tons of sulfur dioxide gas and very fine particulate matter into the stratosphere.
The volcanic plume reacted with water vapor to create a huge sulfate aerosol that impacted global climate by reducing the solar radiation that could reach Earth. The sulfate aerosol also reduced the ozone layer by about 35% by reacting with ozone, and with chlorine that got into the stratosphere from chlorofluorocarbons (CFCs) that were used for many years as spray-can propellants until they were banned.
Impacts and Issues
The Mount Pinatubo eruption has been extensively studied by scientists to try and better understand the effects produced by sulfate aerosols. There are still many unanswered questions. However, there is agreement that sulfate aerosols in the stratosphere scatter radiation coming from the sun and absorb terrestrial (from Earth) radiation, causing a cooling effect.
The effect of sulfate aerosols created from burning fossil fuels has been identified as having a larger influence on solar radiation over North America, Europe, and East Asia, where major population centers are discharging large quantities of combustion emissions from fossil fuels into the atmosphere. The U.S. National Aeronautics and Space Administration (NASA) measures the relative amount of aerosols suspended in the atmosphere using satellites.
WORDS TO KNOW
ACID RAIN: A form of precipitation that is significantly more acidic than neutral water, often produced as the result of industrial processes.
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.
CONDENSATION NUCLEI: Tiny solid airborne particles around which the water droplets or ice crystals that form clouds condense. By providing additional cloud condensation nuclei, aerosol pollution may influence cloud formation and thus climate.
FOSSIL FUELS: Fuels formed by biological processes and transformed into solid or fluid minerals over geological time. Fossil fuels include coal, petroleum, and natural gas. Fossil fuels are non-renewable on the timescale of human civilization, because their natural replenishment would take many millions of years.
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