Environmental Chemistry by Owen Borville 11.5.2025
Earth's atmosphere is unique in that it is chemically active and rich in oxygen. Living things use energy from the sun to break down CO2 to obtain carbon, which they incorporate in their own cells during the process of photosynthesis. The major by-product of photosynthesis is oxygen. Another important source of oxygen is the photodecomposition of water vapor by UV light.
Earth's atmosphere consists mainly of nitrogen gases (78 percent), oxygen (21 percent), argon (0.94 percent), CO2 (0.0412 percent), and small amounts of Ne, He, Kr, and Xe.
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The nitrogen cycle in the Earth's atmosphere is one of the major biogeochemical cycles that involves the atmosphere, soil, water, and living organisms. Molecular nitrogen is a very stable molecule.
Through nitrogen fixation, which is the conversion of molecular nitrogen into nitrogen compounds, atmospheric nitrogen gas is converted into nitrates and other compounds.
Lightening also produces nitrates from nitrogen gas, which then enters the soil through rainwater and helps plants.
N2(g) + O2(g) => electric energy + 2NO(g)
2NO(g) + O2(g) => 2NO2(g)
2NO2(g) + H2O(g) => HNO2(aq) + HNO3(aq)
In the nitrogen cycle, nitric acid is converted to nitrate salts in the soil. Animals use nutrients from plants to make proteins and other essential biomolecules. De-nitrification reverses nitrogen fixation to complete the cycle, where nitrates are converted to nitrogen gas and released into the atmosphere.
The oxygen cycle: Atmospheric oxygen is removed through respiration and various industrial processes, which produce carbon dioxide. Photosynthesis is the major mechanism by which molecular oxygen is regenerated from carbon dioxide and water.
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Scientists divide the atmosphere into several different layers according to temperature variation and composition.
The troposphere is the layer of the atmosphere closest to the Earth's surface. The troposphere is the thinnest layer, but it is where all the dramatic events of weather occur. Temperature decreases linearly with increasing altitude in the region.
The stratosphere contains nitrogen, oxygen, and ozone. Air temperature increases with altitude. UV radiation from the sun triggers the formation of ozone, which prevents harmful UV rays from reaching the Earth's surface.
The mesosphere, the concentration of ozone and other gases is low. Temperature decreases with increasing altitude.
The thermosphere (ionosphere) is the uppermost layer of the atmosphere. The increase in temperature is the result of the bombardment of molecular oxygen and nitrogen and atomic species by energetic particles from the sun.
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Phenomena in the Outer Layers of the Atmosphere: Aurora Borealis and Aurora Australis: Violent eruptions on the surface of the sun, called solar flares, result in the ejection of many electrons and protons into space, which create spectacular celestial light shows called auroras, known as the Northern Lights and Southern Lights.
Electrons and protons collide with the molecules and atoms in the Earth's upper atmosphere, causing them to become ionized and electronically excited. These excited molecules and ions return to the ground state with the emission of light.
An excited oxygen atom emits photons at wavelengths of 558 nm (green) and 630 to 636 nm (red): O*
The blue and violet colors result from the transition in the ionized nitrogen molecule: (N2+*) => (N2+) + hv
hv = energy of a photon of light
Aurora borealis is the name of this phenomenon in the Northern Hemisphere. In the Southern Hemisphere, it is called aurora australis.
---------------------------------------------------------------------------
Mysterious Glow of Space Shuttles: An orange glow on the outside surface of their spacecraft at 300 km above Earth, observed by astronauts in the shuttle. Scientists believe that oxygen atoms interact with NO (nitric oxide) absorbed on the shuttle's surface to form electronically excited NO2 (nitrogen oxide):
O + NO => NO2*
As the NO2* leaves the shell of the spacecraft, it emits photons at a wavelength of 680 nm (orange):
NO2* => NO2 + hv
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Depletion of Ozone in the Stratosphere: The formation of ozone begins with the photodissociation of oxygen molecules by solar radiation (ultraviolet light):
O2 => O + O (for UV < 240 nm)
The highly reactive oxygen atoms combine with oxygen molecules to form ozone:
O (oxygen atom) + O2 (oxygen molecule) + M => O3 + M
where M is some inert substance such as N2. This cycle happens continuously.
Ozone itself absorbs UV light between 200 and 300 nm: O3 => O + O2 (in the presence of UV). The process continues when O and O2 recombine to form O3. Ozone shields and protects humans and life on Earth from harmful ultraviolet UV radiation. The formation and destruction of ozone is a dynamic equilibrium that maintains a constant concentration of ozone in the stratosphere.
Since the 1970s, there has been concern about CFCs(chlorofluorocarbons) damaging the ozone layer, specifically chlorine atoms which catalytically destroy ozone molecules.
CFCs slowly diffuse unchanged to the stratosphere, where UV radiation causes them to decompose.
CFCl3 =>CFCl2 + Cl
CF2Cl2 => CF2Cl + Cl
The reactive chlorine atoms then undergo the following reactions:
Cl + O3 => ClO + O2
ClO + O => Cl + O2
The overall result is the net removal of an O3 molecule from the stratosphere: O3 + O => 2O2 The Cl atom is the catalyst. One Cl atom can destroy up to 100,000 O3 molecules. The concentration of O3 decreases in regions that have high amounts of ClO.
Nitrogen oxides are another compound that can destroy stratospheric ozone:
O3 => O2 + O
NO + O3 => NO2 + O2
NO2 + O => NO + O2
-----------------------------
2O3 => 3O2 Overall reaction. NO is the catalyst and NO2 is the intermediate.
Polar Ozone Holes: the Antarctic Ozone Hole develops in late winter, depleting the stratospheric ozone over Antarctica by as much as 50 percent.
A stream of air known as the Polar Vortex circles Antarctica in the winter. Air trapped within this vortex becomes extremely cold during the polar night, leading to the formation of ice particles known as polar stratospheric clouds (or PSCs)
PSCs provide a surface for reactions converting HCl and ClONO2 to more reactive chlorine molecules: HCl + ClONO2 => Cl2 + HNO3
By early spring, the sunlight splits molecular chlorine into chlorine atoms, which then attack ozone: Cl2 + hv => 2Cl
hv represents light energy, which can come from sunlight.
The vortex is not as severe in the warmer Arctic region, where the vortex does not last quite as long.
Nations throughout the world have realized the need to substantially limit or stop the production of CFCs. An strong effort is underway to find CFC substitutes that are not harmful to the ozone layer.
-----------------------------------------------------------------------
Volcanoes and volcanic eruptions are instrumental in forming large parts of the Earth's crust. Molten rock, called magma, in the upper mantle layer of the Earth, rises to the surface and generates volcanic eruptions.
An active volcano emits gases, liquids, and solids: The gases spewed into the atmosphere include N2, CO2, HCl, HF, H2S, and H2O(l) (water vapor). Volcanoes are the source of about two-thirds of the sulfur in the air.
At high temperatures, the hydrogen sulfide gas given off by a volcano is oxidized by air: 2H2S(g) + 3O2(g) => 2SO2(g) + 2H2O(g)
Some of the SO2 is reduced by more H2S from the volcano to elemental sulfur and water: 2H2S(g) + SO2(g) => 3S(s) + 2H2O(g)
The rest of the SO2 is released into the atmosphere, where it reacts with water to form acid rain. Aerosols given off by volcanic eruptions destroy ozone and affect climate by creating a localized cooling effect.
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The Greenhouse Effect is the trapping of heat near the Earth's surface by gases in the atmosphere, particularly carbon dioxide. The transfer of CO2 to and from the atmosphere is an essential part of the carbon cycle. CO2 is produced when any form of carbon or a carbon-containing compound is burned in an excess of oxygen.
The carbon cycle is the natural process in the Earth's ecosystems where carbon atoms are exchanged among the atmosphere, oceans, land, soil, and living organisms, including plants and animals by respiration and decomposition in the soil.
Sources of CO2: Carbohydrates can give off CO2 when heated or treated with acid:
CaCO3(s) + heat => CaO(s) + CO2(g)
CaCO3(s) + 2HCl(aq)(acid) => CaCl2(aq) + H2O(l) + CO2(g)
Carbon dioxide is also a by-product of the fermentation of sugar:
C6H12O6(aq)(glucose) => 2C2H5OH(aq)(ethanol)+ 2CO2(g)
Animals respire and release CO2 as an end product of metabolism: C6H12O6(aq) + 6O2(g) => 6CO2(g) + 6H2O(l).
Volcanic activity is also a major sources of CO2.
Carbon dioxide is removed from the atmosphere by photosynthetic plants and certain microorganisms: 6CO2(g) +6H2O(l) => C6H12O6(aq) + 6CO2(g)
After plants and animals die, the carbon in their tissues is oxidized to CO2 and returns to the atmosphere. There is dynamic equilibrium between atmospheric CO2 and carbonates in the oceans and lakes.
Much of the solar radiant energy received by Earth is in the visible region of the spectrum. Thermal radiation emitted by Earth's surface is characterized by wavelengths in the IR (infrared) region. The outgoing IR radiation can be absorbed by water and carbon dioxide, but not by nitrogen and oxygen.
The incoming radiation from the sun is much higher energy and has much smaller wavelength than the outgoing terrestrial radiation, which is much lower energy and has much larger wavelength.
All molecules vibrate by stretching, compressing, and bending and the energy associated with molecular vibration is quantized.
To absorb a photon in the IR region, the dipole moment of the molecule must change during the course of a vibration. If the molecule is homonuclear, there can be no change in the dipole moment and the molecule has a zero dipole moment. Such molecules are IR-inactive because they cannot absorb IR radiation.
All heteronuclear diatomic molecules are IR-active. They can absorb IR radiation because their dipole moments change. A polyatomic molecule can vibrate in more than one way. Water, for example, is IR active and can vibrate in three different ways.
Carbon dioxide has linear geometry and is non-polar. Carbon dioxide is IR active, along with CO.
Receiving a photon in the IR region, a molecule of H2O or CO2 is promoted to a higher vibrational energy level:
H2O + hv => H2O*
CO2 + hv => CO2*
These excited molecules lose their excess energy either by collision with other molecules or by spontaneous radiation.
The concentration of CO2 has been steadily rising since the turn of the century as a result of the burning of fossil fuels, including petroleum, natural gas, and coal.
Sources of CO2 emission come from electricity, transportation, industry, residential and commercial use. The current rate of increase is more than 1 ppm by volume per year, which is equivalent to roughly 1 x 10^10 tons of CO2.
Other greenhouse gases contribute to gradual warming of the atmosphere, in addition to CO2, including methane (CH4), nitrous oxide (N2O), and fluorinated gases.
Lowering carbon dioxide emissions to reduce greenhouse gases would include: improving energy efficiency in automobiles and households or reducing carbon dioxide emissions in these, developing non-fossil fuel energy sources, stop using CFCs, recovery of methane gas generated at landfills, reduction of natural gas leakages, and preservation of forests.
----------------------------------------------------------------------------
Acid rain causes much damage to stone buildings and structures every year throughout the world. Acid rain is also known as stone leprosy by some scientists to describe the corrosion of stone by acid rain. Acid rain is also toxic to vegetation and aquatic life.
Precipitation in the northeastern U.S. has an average pH of about 4.3. Sulfur dioxide (SO2) and nitrogen oxides from auto emissions are believed to be responsible for the high acidity of precipitation and rainwater. Acidic oxides, such as SO2, react with water to produce acids. Sources of atmospheric SO2 include volcanic eruptions.
Many metals occur in nature combined with sulfur. Separating these metals often includes smelting, or roasting the ores (heating the metal sulfide in air to form the metal oxide and SO2): 2ZnS(s) + 3O2(g) => 2ZnO(s) + 2SO2(g) The metal oxide can be reduced more easily than the sulfide to separate the metal.
Most SO2 produced by humans comes from industrial burning of fossil fuels, power plants, and homes. Up to 60 million tons of SO2 are released into the atmosphere each year. Almost all SO2 produced by humans is oxidized to H2SO4 in the form of aerosol, which becomes acid rain.
Conversion of SO2 to H2SO4 is believed to be initiated by the hydroxyl OH:
OH + SO2 => HOSO2
HOSO3 + O2 => HO2 + SO3
SO3 + H2O => H2SO4: Reaction with water to form sulfuric acid.
CaCO3(s) + H2SO4(aq) => CaSO4(s) + H2O(l) + CO2(g): Acid rain corrodes limestone and marble.
Pollution from SO2 can be reduced by (1) removing sulfur from fossil fuels before combustion, which is difficult. (2) removing SO2 as it is formed from limestone.
Limestone is injected into the power plant boiler or furnace along with the coal. At high temperatures, decomposition occurs: CaCO3(s)(limestone) => CaO(s) + CO2(g)(quicklime). The quicklime reacts with SO2 to form calcium sulfite and some calcium sulfate: CaO(s) + SO2(g) => CaSO3(s)
2CaO(s) + 2SO2(g) +O2(g) => 2CaSO4(s)
Quicklime is also added to lakes and soils in a process called liming to reduce their acidity.
Photochemical Smog: The term smog was used to describe the smoke and fog that accompanied London, UK in the 1950s. The primary cause of this cloud was sulfur dioxide. Photochemical smog is formed by the reactions of automobile exhaust in the presence of sunlight.
Automobile exhaust contains mainly NO, CO, and other hydrocarbons. These gases are primary pollutants because they set in motion a series of photochemical reactions that produce secondary pollutants. The secondary pollutants, mainly NO2 and O3 are responsible for smog.
Photochemical smog is produced by atmospheric N2 and O2 at high temperatures inside an automobile engine: N2(g) + O2(g) => 2NO(g). Nitric oxide is then oxidized to nitrogen dioxide. 2NO(g) + O2(g) => 2NO2(g)
Sunlight causes the photochemical decomposition: NO2(g) + hv => NO(g) + O(g)
Atomic oxygen is a highly reactive species that can initiate the formation of ozone: O(g) + O2(g) + M => O3(g) + M, where M is some inert substance such as N2.
Ozone damages the Carbon=Carbon double bonds in rubber, which can cause automobile tires to crack. Similar reactions are also damaging to lung tissues and other biological substances.
Primary and secondary pollutant concentrations vary significantly with time due to daily cycles, weather patterns, and seasonal changes.
The oxidation of hydrocarbons produces various organic intermediates, which are less volatile than the hydrocarbons themselves. These substances condense into small droplets of liquid called aerosols and cause the air look hazy.
Efforts to reduce primary pollutants include installing catalytic converters (3-way) on automobiles that oxidize hydrocarbons to CO2 and H2O and reduces nitrogen oxides into N2 and O2.
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Radon is an element of the Periodic Table Group 18 and a Noble Gas. Radon is an intermediate product of the radioactive decay of uranium-238. All isotopes of radon are radioactive, but radon-222 is the most hazardous because it has the longest half-life (3.8 days). Radon is generated mostly from the phosphate minerals of uranium.
High levels of radon have been detected in homes built on reclaimed land above uranium mill tailing deposits. The colorless, odorless, and tasteless radon gas enters a building through tiny cracks in the basement floor. Radon-222 is an alpha emitter.
When radon decays, it produces radioactive polonum-214 and polonium-218, which can build up to high levels in an enclosed space. These solid radioactive particles are inhaled into the lungs and deposited in the respiratory tract. Over a long period of time, the particles emitted by polonium and its decay products can cause lung cancer.
The first step to stop or control radon pollution indoors is to measure the radon level in the basement with a reliable test kit. If the radon level is high , then the house must be regularly ventilated.
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Indoor pollution can also include carbon dioxide (CO2) and carbon monoxide (CO), which are products of combustion. Indoor sources of these gases are gas cooking ranges, wood stoves, space heaters, tobacco smoke, human respiration, and exhaust fumes from automobiles in garages.
Carbon dioxide is not a toxic gas, but it does have an asphyxiating effect by reducing the oxygen in the air and causing headaches, dizziness, rapid heart rate, and short breath. Adequate ventilation is the solution to CO2 pollution.
Carbon monoxide is highly poisonous and its toxicity is in its ability to bind very strongly to hemoglobin, the oxygen carrier in the blood. Affinity of hemoglobin is about 200 times greater than it is for O2. The first aid response to CO poisoning is to remove the victim immediately to an area with a plentiful oxygen supply.
Formaldehyde (CH2O) is a liquid used as a preservative for laboratory specimens. Industrial use of formaldehyde resin is as a bonding agent in building and furniture construction materials. Low concentrations of formaldehyde in the air can cause drowsiness, nausea, headaches, and other respiratory problems.
Because formaldehyde is a reducing agent, devices have been constructed to remove it by means of a redox reaction. Proper ventilation is the best way to remove formaldehyde.
Earth's atmosphere is unique in that it is chemically active and rich in oxygen. Living things use energy from the sun to break down CO2 to obtain carbon, which they incorporate in their own cells during the process of photosynthesis. The major by-product of photosynthesis is oxygen. Another important source of oxygen is the photodecomposition of water vapor by UV light.
Earth's atmosphere consists mainly of nitrogen gases (78 percent), oxygen (21 percent), argon (0.94 percent), CO2 (0.0412 percent), and small amounts of Ne, He, Kr, and Xe.
-------------------------------------------------
The nitrogen cycle in the Earth's atmosphere is one of the major biogeochemical cycles that involves the atmosphere, soil, water, and living organisms. Molecular nitrogen is a very stable molecule.
Through nitrogen fixation, which is the conversion of molecular nitrogen into nitrogen compounds, atmospheric nitrogen gas is converted into nitrates and other compounds.
Lightening also produces nitrates from nitrogen gas, which then enters the soil through rainwater and helps plants.
N2(g) + O2(g) => electric energy + 2NO(g)
2NO(g) + O2(g) => 2NO2(g)
2NO2(g) + H2O(g) => HNO2(aq) + HNO3(aq)
In the nitrogen cycle, nitric acid is converted to nitrate salts in the soil. Animals use nutrients from plants to make proteins and other essential biomolecules. De-nitrification reverses nitrogen fixation to complete the cycle, where nitrates are converted to nitrogen gas and released into the atmosphere.
The oxygen cycle: Atmospheric oxygen is removed through respiration and various industrial processes, which produce carbon dioxide. Photosynthesis is the major mechanism by which molecular oxygen is regenerated from carbon dioxide and water.
---------------------------------------------------------------------------------------------------
Scientists divide the atmosphere into several different layers according to temperature variation and composition.
The troposphere is the layer of the atmosphere closest to the Earth's surface. The troposphere is the thinnest layer, but it is where all the dramatic events of weather occur. Temperature decreases linearly with increasing altitude in the region.
The stratosphere contains nitrogen, oxygen, and ozone. Air temperature increases with altitude. UV radiation from the sun triggers the formation of ozone, which prevents harmful UV rays from reaching the Earth's surface.
The mesosphere, the concentration of ozone and other gases is low. Temperature decreases with increasing altitude.
The thermosphere (ionosphere) is the uppermost layer of the atmosphere. The increase in temperature is the result of the bombardment of molecular oxygen and nitrogen and atomic species by energetic particles from the sun.
---------------------------------------------------------------------------
Phenomena in the Outer Layers of the Atmosphere: Aurora Borealis and Aurora Australis: Violent eruptions on the surface of the sun, called solar flares, result in the ejection of many electrons and protons into space, which create spectacular celestial light shows called auroras, known as the Northern Lights and Southern Lights.
Electrons and protons collide with the molecules and atoms in the Earth's upper atmosphere, causing them to become ionized and electronically excited. These excited molecules and ions return to the ground state with the emission of light.
An excited oxygen atom emits photons at wavelengths of 558 nm (green) and 630 to 636 nm (red): O*
The blue and violet colors result from the transition in the ionized nitrogen molecule: (N2+*) => (N2+) + hv
hv = energy of a photon of light
Aurora borealis is the name of this phenomenon in the Northern Hemisphere. In the Southern Hemisphere, it is called aurora australis.
---------------------------------------------------------------------------
Mysterious Glow of Space Shuttles: An orange glow on the outside surface of their spacecraft at 300 km above Earth, observed by astronauts in the shuttle. Scientists believe that oxygen atoms interact with NO (nitric oxide) absorbed on the shuttle's surface to form electronically excited NO2 (nitrogen oxide):
O + NO => NO2*
As the NO2* leaves the shell of the spacecraft, it emits photons at a wavelength of 680 nm (orange):
NO2* => NO2 + hv
--------------------------------------------------------------------------
Depletion of Ozone in the Stratosphere: The formation of ozone begins with the photodissociation of oxygen molecules by solar radiation (ultraviolet light):
O2 => O + O (for UV < 240 nm)
The highly reactive oxygen atoms combine with oxygen molecules to form ozone:
O (oxygen atom) + O2 (oxygen molecule) + M => O3 + M
where M is some inert substance such as N2. This cycle happens continuously.
Ozone itself absorbs UV light between 200 and 300 nm: O3 => O + O2 (in the presence of UV). The process continues when O and O2 recombine to form O3. Ozone shields and protects humans and life on Earth from harmful ultraviolet UV radiation. The formation and destruction of ozone is a dynamic equilibrium that maintains a constant concentration of ozone in the stratosphere.
Since the 1970s, there has been concern about CFCs(chlorofluorocarbons) damaging the ozone layer, specifically chlorine atoms which catalytically destroy ozone molecules.
CFCs slowly diffuse unchanged to the stratosphere, where UV radiation causes them to decompose.
CFCl3 =>CFCl2 + Cl
CF2Cl2 => CF2Cl + Cl
The reactive chlorine atoms then undergo the following reactions:
Cl + O3 => ClO + O2
ClO + O => Cl + O2
The overall result is the net removal of an O3 molecule from the stratosphere: O3 + O => 2O2 The Cl atom is the catalyst. One Cl atom can destroy up to 100,000 O3 molecules. The concentration of O3 decreases in regions that have high amounts of ClO.
Nitrogen oxides are another compound that can destroy stratospheric ozone:
O3 => O2 + O
NO + O3 => NO2 + O2
NO2 + O => NO + O2
-----------------------------
2O3 => 3O2 Overall reaction. NO is the catalyst and NO2 is the intermediate.
Polar Ozone Holes: the Antarctic Ozone Hole develops in late winter, depleting the stratospheric ozone over Antarctica by as much as 50 percent.
A stream of air known as the Polar Vortex circles Antarctica in the winter. Air trapped within this vortex becomes extremely cold during the polar night, leading to the formation of ice particles known as polar stratospheric clouds (or PSCs)
PSCs provide a surface for reactions converting HCl and ClONO2 to more reactive chlorine molecules: HCl + ClONO2 => Cl2 + HNO3
By early spring, the sunlight splits molecular chlorine into chlorine atoms, which then attack ozone: Cl2 + hv => 2Cl
hv represents light energy, which can come from sunlight.
The vortex is not as severe in the warmer Arctic region, where the vortex does not last quite as long.
Nations throughout the world have realized the need to substantially limit or stop the production of CFCs. An strong effort is underway to find CFC substitutes that are not harmful to the ozone layer.
-----------------------------------------------------------------------
Volcanoes and volcanic eruptions are instrumental in forming large parts of the Earth's crust. Molten rock, called magma, in the upper mantle layer of the Earth, rises to the surface and generates volcanic eruptions.
An active volcano emits gases, liquids, and solids: The gases spewed into the atmosphere include N2, CO2, HCl, HF, H2S, and H2O(l) (water vapor). Volcanoes are the source of about two-thirds of the sulfur in the air.
At high temperatures, the hydrogen sulfide gas given off by a volcano is oxidized by air: 2H2S(g) + 3O2(g) => 2SO2(g) + 2H2O(g)
Some of the SO2 is reduced by more H2S from the volcano to elemental sulfur and water: 2H2S(g) + SO2(g) => 3S(s) + 2H2O(g)
The rest of the SO2 is released into the atmosphere, where it reacts with water to form acid rain. Aerosols given off by volcanic eruptions destroy ozone and affect climate by creating a localized cooling effect.
----------------------------------------------------------------------------------
The Greenhouse Effect is the trapping of heat near the Earth's surface by gases in the atmosphere, particularly carbon dioxide. The transfer of CO2 to and from the atmosphere is an essential part of the carbon cycle. CO2 is produced when any form of carbon or a carbon-containing compound is burned in an excess of oxygen.
The carbon cycle is the natural process in the Earth's ecosystems where carbon atoms are exchanged among the atmosphere, oceans, land, soil, and living organisms, including plants and animals by respiration and decomposition in the soil.
Sources of CO2: Carbohydrates can give off CO2 when heated or treated with acid:
CaCO3(s) + heat => CaO(s) + CO2(g)
CaCO3(s) + 2HCl(aq)(acid) => CaCl2(aq) + H2O(l) + CO2(g)
Carbon dioxide is also a by-product of the fermentation of sugar:
C6H12O6(aq)(glucose) => 2C2H5OH(aq)(ethanol)+ 2CO2(g)
Animals respire and release CO2 as an end product of metabolism: C6H12O6(aq) + 6O2(g) => 6CO2(g) + 6H2O(l).
Volcanic activity is also a major sources of CO2.
Carbon dioxide is removed from the atmosphere by photosynthetic plants and certain microorganisms: 6CO2(g) +6H2O(l) => C6H12O6(aq) + 6CO2(g)
After plants and animals die, the carbon in their tissues is oxidized to CO2 and returns to the atmosphere. There is dynamic equilibrium between atmospheric CO2 and carbonates in the oceans and lakes.
Much of the solar radiant energy received by Earth is in the visible region of the spectrum. Thermal radiation emitted by Earth's surface is characterized by wavelengths in the IR (infrared) region. The outgoing IR radiation can be absorbed by water and carbon dioxide, but not by nitrogen and oxygen.
The incoming radiation from the sun is much higher energy and has much smaller wavelength than the outgoing terrestrial radiation, which is much lower energy and has much larger wavelength.
All molecules vibrate by stretching, compressing, and bending and the energy associated with molecular vibration is quantized.
To absorb a photon in the IR region, the dipole moment of the molecule must change during the course of a vibration. If the molecule is homonuclear, there can be no change in the dipole moment and the molecule has a zero dipole moment. Such molecules are IR-inactive because they cannot absorb IR radiation.
All heteronuclear diatomic molecules are IR-active. They can absorb IR radiation because their dipole moments change. A polyatomic molecule can vibrate in more than one way. Water, for example, is IR active and can vibrate in three different ways.
Carbon dioxide has linear geometry and is non-polar. Carbon dioxide is IR active, along with CO.
Receiving a photon in the IR region, a molecule of H2O or CO2 is promoted to a higher vibrational energy level:
H2O + hv => H2O*
CO2 + hv => CO2*
These excited molecules lose their excess energy either by collision with other molecules or by spontaneous radiation.
The concentration of CO2 has been steadily rising since the turn of the century as a result of the burning of fossil fuels, including petroleum, natural gas, and coal.
Sources of CO2 emission come from electricity, transportation, industry, residential and commercial use. The current rate of increase is more than 1 ppm by volume per year, which is equivalent to roughly 1 x 10^10 tons of CO2.
Other greenhouse gases contribute to gradual warming of the atmosphere, in addition to CO2, including methane (CH4), nitrous oxide (N2O), and fluorinated gases.
Lowering carbon dioxide emissions to reduce greenhouse gases would include: improving energy efficiency in automobiles and households or reducing carbon dioxide emissions in these, developing non-fossil fuel energy sources, stop using CFCs, recovery of methane gas generated at landfills, reduction of natural gas leakages, and preservation of forests.
----------------------------------------------------------------------------
Acid rain causes much damage to stone buildings and structures every year throughout the world. Acid rain is also known as stone leprosy by some scientists to describe the corrosion of stone by acid rain. Acid rain is also toxic to vegetation and aquatic life.
Precipitation in the northeastern U.S. has an average pH of about 4.3. Sulfur dioxide (SO2) and nitrogen oxides from auto emissions are believed to be responsible for the high acidity of precipitation and rainwater. Acidic oxides, such as SO2, react with water to produce acids. Sources of atmospheric SO2 include volcanic eruptions.
Many metals occur in nature combined with sulfur. Separating these metals often includes smelting, or roasting the ores (heating the metal sulfide in air to form the metal oxide and SO2): 2ZnS(s) + 3O2(g) => 2ZnO(s) + 2SO2(g) The metal oxide can be reduced more easily than the sulfide to separate the metal.
Most SO2 produced by humans comes from industrial burning of fossil fuels, power plants, and homes. Up to 60 million tons of SO2 are released into the atmosphere each year. Almost all SO2 produced by humans is oxidized to H2SO4 in the form of aerosol, which becomes acid rain.
Conversion of SO2 to H2SO4 is believed to be initiated by the hydroxyl OH:
OH + SO2 => HOSO2
HOSO3 + O2 => HO2 + SO3
SO3 + H2O => H2SO4: Reaction with water to form sulfuric acid.
CaCO3(s) + H2SO4(aq) => CaSO4(s) + H2O(l) + CO2(g): Acid rain corrodes limestone and marble.
Pollution from SO2 can be reduced by (1) removing sulfur from fossil fuels before combustion, which is difficult. (2) removing SO2 as it is formed from limestone.
Limestone is injected into the power plant boiler or furnace along with the coal. At high temperatures, decomposition occurs: CaCO3(s)(limestone) => CaO(s) + CO2(g)(quicklime). The quicklime reacts with SO2 to form calcium sulfite and some calcium sulfate: CaO(s) + SO2(g) => CaSO3(s)
2CaO(s) + 2SO2(g) +O2(g) => 2CaSO4(s)
Quicklime is also added to lakes and soils in a process called liming to reduce their acidity.
Photochemical Smog: The term smog was used to describe the smoke and fog that accompanied London, UK in the 1950s. The primary cause of this cloud was sulfur dioxide. Photochemical smog is formed by the reactions of automobile exhaust in the presence of sunlight.
Automobile exhaust contains mainly NO, CO, and other hydrocarbons. These gases are primary pollutants because they set in motion a series of photochemical reactions that produce secondary pollutants. The secondary pollutants, mainly NO2 and O3 are responsible for smog.
Photochemical smog is produced by atmospheric N2 and O2 at high temperatures inside an automobile engine: N2(g) + O2(g) => 2NO(g). Nitric oxide is then oxidized to nitrogen dioxide. 2NO(g) + O2(g) => 2NO2(g)
Sunlight causes the photochemical decomposition: NO2(g) + hv => NO(g) + O(g)
Atomic oxygen is a highly reactive species that can initiate the formation of ozone: O(g) + O2(g) + M => O3(g) + M, where M is some inert substance such as N2.
Ozone damages the Carbon=Carbon double bonds in rubber, which can cause automobile tires to crack. Similar reactions are also damaging to lung tissues and other biological substances.
Primary and secondary pollutant concentrations vary significantly with time due to daily cycles, weather patterns, and seasonal changes.
The oxidation of hydrocarbons produces various organic intermediates, which are less volatile than the hydrocarbons themselves. These substances condense into small droplets of liquid called aerosols and cause the air look hazy.
Efforts to reduce primary pollutants include installing catalytic converters (3-way) on automobiles that oxidize hydrocarbons to CO2 and H2O and reduces nitrogen oxides into N2 and O2.
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Radon is an element of the Periodic Table Group 18 and a Noble Gas. Radon is an intermediate product of the radioactive decay of uranium-238. All isotopes of radon are radioactive, but radon-222 is the most hazardous because it has the longest half-life (3.8 days). Radon is generated mostly from the phosphate minerals of uranium.
High levels of radon have been detected in homes built on reclaimed land above uranium mill tailing deposits. The colorless, odorless, and tasteless radon gas enters a building through tiny cracks in the basement floor. Radon-222 is an alpha emitter.
When radon decays, it produces radioactive polonum-214 and polonium-218, which can build up to high levels in an enclosed space. These solid radioactive particles are inhaled into the lungs and deposited in the respiratory tract. Over a long period of time, the particles emitted by polonium and its decay products can cause lung cancer.
The first step to stop or control radon pollution indoors is to measure the radon level in the basement with a reliable test kit. If the radon level is high , then the house must be regularly ventilated.
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Indoor pollution can also include carbon dioxide (CO2) and carbon monoxide (CO), which are products of combustion. Indoor sources of these gases are gas cooking ranges, wood stoves, space heaters, tobacco smoke, human respiration, and exhaust fumes from automobiles in garages.
Carbon dioxide is not a toxic gas, but it does have an asphyxiating effect by reducing the oxygen in the air and causing headaches, dizziness, rapid heart rate, and short breath. Adequate ventilation is the solution to CO2 pollution.
Carbon monoxide is highly poisonous and its toxicity is in its ability to bind very strongly to hemoglobin, the oxygen carrier in the blood. Affinity of hemoglobin is about 200 times greater than it is for O2. The first aid response to CO poisoning is to remove the victim immediately to an area with a plentiful oxygen supply.
Formaldehyde (CH2O) is a liquid used as a preservative for laboratory specimens. Industrial use of formaldehyde resin is as a bonding agent in building and furniture construction materials. Low concentrations of formaldehyde in the air can cause drowsiness, nausea, headaches, and other respiratory problems.
Because formaldehyde is a reducing agent, devices have been constructed to remove it by means of a redox reaction. Proper ventilation is the best way to remove formaldehyde.