4AE3 U5 C2 Obj 2.pdf

Unit A-5 • Introduction to Plant Operations and the Environment Objective 2 Identify the common greenhouse and acid rain causing gases and describe their effects. Greenhouse Effect The Earth has existed for a considerable time in an equilibrium state, where the amount of energy received from the s...

Unit A-5 • Introduction to Plant Operations and the Environment Objective 2 Identify the common greenhouse and acid rain causing gases and describe their effects. Greenhouse Effect The Earth has existed for a considerable time in an equilibrium state, where the amount of energy received from the sun is balanced with an equal amount of energy radiated from the Earth back into space. X-rays and high energy ultraviolet light encounter upper atmospheric components such as oxygen and ozone. Here, they are absorbed or reflected back into space. Slightly lower energy radiation (such as visible light and infrared radiation) passes through the atmosphere to ground level. At ground level, it is largely absorbed and eventually radiated back towards space at an even lower energy level. In this way, energy equilibrium is maintained. Greenhouse gases allow high energy radiation to pass through, but restrict the transmission of the lower energy radiation that would normally move towards space. Without greenhouse gases in the atmosphere, the Earth’s average temperature would be about 40 degrees Celsius colder than it is today, and the planet could not support life. Therefore, greenhouse gases are not only beneficial but necessary for life on Earth. A visual representation of the Greenhouse Effect is shown in Figure 2. The sunlight that initially gets through the atmosphere is mostly low energy (visible and infrared) with the UV mostly being trapped. Some energy, which would have radiated back out through the atmosphere, is trapped by greenhouse gases and converted to heat. This causes a temperature rise in the atmosphere and on the Earth’s surface. The stable concentration of greenhouse gases, under natural conditions, accounts for the stability of the Earth’s overall average temperature over many centuries. However, atmospheric greenhouse gas concentrations have increased since the Industrial Revolution of the 1800s due to human activity. With an increase in greenhouse gas concentration, more outgoing radiation is trapped by the atmosphere. This causes an increase in the Earth’s average temperatures. The most common greenhouse gases include: • Carbon Dioxide • Methane • Nitrous Oxide • Chlorofluorocarbons • Fluorinated Gases • Water Vapour • Ozone Carbon dioxide, methane, and water vapour exist naturally. They have always been atmospheric components necessary for human life. Methane has always existed in the atmosphere from natural sources; however, industrial activity has greatly contributed to methane concentrations in the atmosphere. Nitrous oxide normally exists in small amounts in the atmosphere. Like methane, the greatest contributor to atmospheric nitrous oxide has been human activity. Chlorofluorocarbons and fluorinated gases exist entirely due to human activity. 2-10 4th Class Edition 3 • Part A Gas and Noise Emissions • Chapter 2 Figure 2 – Greenhouse Effect Some sunlight is reflected and some reaches the earth ATMOSPHERE Greenhouse gases trap heat, warming the earth Effects of the Various Greenhouse Gases Not all GHGs are created equal. Some have a higher potential to affect the Earth. In order to compare the effects of various GHGs, the Global Warming Potential (GWP) scale was created. Carbon Dioxide was made the standard against which all other greenhouse gases would be compared. As such, CO2 has a GWP of 1. Methane has a GWP of 25. This means that methane is 25 times as potent a greenhouse gas as carbon dioxide. Nitrous Oxide has a GWP of 298. CFCs and fluorinated gases are called high GWP gases, since their GWP is well into the thousands. Table 2 lists some of the greenhouse gases recognized by Environment Canada, and compares their global warming potentials. Table 2 – GWP of Various Greenhouse Gases Greenhouse Gas Formula Carbon dioxide CO2 1 Methane CH4 25 Nitrous oxide N2O 298 Sulfur hexafluoride SF6 22 800 Nitrogen trifluoride NF3 17 200 HFC-134a CH2FCF3 1 430 Perfluoromethane CF4 7 390 Perfluoroethane C2F6 12 200 4th Class Edition 3 • Part A GWP 2-11 Unit A-5 • Introduction to Plant Operations and the Environment Carbon Dioxide (CO2) Carbon dioxide is an important greenhouse gas. It accounts for about 76% of global greenhouse gas emissions. CO2 emissions and other GHGs are rising. CO2 does not remain in the atmosphere. About one-half of the CO2 emitted is used by plants or absorbed by the oceans. The CO2 absorbed by the oceans is eventually transferred by an extremely slow process to ocean sediments. The rest stays in the atmosphere. Methane (CH4) Methane (CH4) is believed to be responsible for about 16% of global greenhouse gas emissions. The carbon in methane makes it a heat-trapping gas, like carbon dioxide, but it is about thirty times more active than CO2. However, while the greenhouse effect of methane is much higher than that of CO2, methane has an atmospheric life time of about 12 years. This is much shorter than carbon dioxide’s. Some scientists believe that methane prevents the atmosphere from eliminating CFCs. Nitrous Oxide (N2O) Nitrous oxide (“laughing gas”) is very stable. It lasts an estimated 150 years or longer in the atmosphere. It contributes to the greenhouse effect, and accounts for about 6% of the problem. When it rises to the stratosphere, it is also responsible for destroying ozone. Chlorofluorocarbons (CFCs) Chlorofluorocarbons are a group of common refrigerants, solvents, and aerosol propellants that were widely used in industry years ago. They are very stable man-made compounds that destroy ozone after they reach the stratosphere. Ozone shields the planet from harmful UV radiation that can cause cancer. In the lower atmosphere, CFCs absorb infrared rays about 10 000 times more effectively than carbon dioxide, making them powerful greenhouse gases. The release of CFCs and other ozone depleting substances has decreased since the mid-1990’s. Multi-national agreements have restricted and ultimately eliminated their use. Fluorinated Gases Fluorinated gases have a very high global warming potential. However, they do not damage the ozone layer, which is why they were proposed as viable replacements for CFCs. Emissions of fluorinated gases has risen in the United States by 77% and in Europe by 60% between 1990 and 2014. New strategies and policies are being developed to deal with rising fluorinated gas emissions. In 2010, fluorinated gas emissions made up 2% of global GHG emissions. Water Vapour Water vapour is the most important and most potent of all greenhouse gases. It absorbs far more radiant energy, from a broader wave spectrum, than CO2. The ability for air to retain water vapour is dependent on the temperature of the air. As a given sample of air increases in temperature, its relative humidity decreases. This allows (but does not mandate) an increase in absolute humidity. The traditional method by which water vapour enters the atmosphere is by: a) Evaporation from bodies of water b) Transpiration from plants c) Naturally-occurring combustion due to forest and brush fires d) Respiration from animals Since the industrial revolution, greater quantities of water vapour have entered the air from industrial activity. This includes combustion of hydrocarbon fuels and evaporative cooling processes. In addition, water vapour carries latent heat to the atmosphere, which adds to the atmospheric energy content. 2-12 4th Class Edition 3 • Part A Gas and Noise Emissions • Chapter 2 Traditionally, greenhouse gas models have not accounted for the effect of water vapour as a greenhouse gas. As well, the scientific community has been reluctant to assign a GWP value to water vapour. This is because the overall effects of atmospheric water vapour on climate change have been difficult to model. In part, this is due to wide variations in atmospheric water vapour content based on latitude, proximity to land masses, and proximity to bodies of water. Ozone In the stratosphere, ozone is very beneficial because it absorbs cancer-causing ultraviolet radiation. However, in the troposphere, ozone is a greenhouse gas. Like water vapour, quantifying the greenhouse gas potency of ozone is difficult. This is because ozone is not present in uniform concentrations across the globe. Figure 3 shows the United States EPA 2014 estimate for relative amounts of greenhouse gas emissions. In their analysis, they differentiate between industrial and land-use CO2 emissions. Figure 3 – Global Greenhouse Gas Emissions as a Percentage of the Total - 2014 (Data Courtesy of U.S. EPA) 4th Class Edition 3 • Part A 2-13 Unit A-5 • Introduction to Plant Operations and the Environment Figure 4 shows the distribution of greenhouse gas emissions by economic sector in Canada during 2014. The Oil and Gas and Transportation sectors collectively produce around 50% of CO2 emissions. Figure 4 – Greenhouse Gas Emissions by Sector - 2014 (Data Courtesy of Environment Canada) Acid Rain Acid rain is formed when NOX and SOX in the atmosphere undergo complex reactions with water vapour and sunlight. The products that result from these reactions include a number of sulfur and nitrogen aqueous compounds, including sulfuric, sulfurous, nitric, and nitrous acids. These precipitate with rain, snow, hail, sleet, and fog. The contaminants which form acid rain can be carried in the atmosphere over great distances from their source. Until technology was applied to clean the flue gases, the nickel smelters around Sudbury, Ontario carried NOX and SOX emissions as far as Quebec, and acidified the lakes and rivers. Smog from California deposits pollution in the snows of Colorado. The snows melt and the acidic runoff leaches hazardous minerals from the mountains. Some of the meltwater returns in the rivers as a water source for California. Effects of Acid Rain on Lakes and Rivers The normal or healthy pH level in lakes is about 5.5 or higher. As the acid levels increase in a lake, the pH decreases. The first to be affected is microscopic life, and this affects the entire food chain. Greater acidity can interfere with the reproductive cycle of aquatic animals. Metals leached from the soil by the acidic liquids reach higher concentrations than normal. This can restrict the ability of some aquatic animals to breathe properly. For example, fish gills can become deformed and the fish can suffocate. 2-14 4th Class Edition 3 • Part A Gas and Noise Emissions • Chapter 2 In a landscape affected by acid rain, the first snowmelt of spring releases a surge of acidic runoff that can lower the natural pH of a still body of water such as a lake. This periodic acidification may only be temporary. Even so, many eggs and hatchlings may not survive. Over time, continuous exposure to acid rain can result in the entire ecosystem within the lake being negatively impacted. Lakes which are affected by acid rain to such an extent that they cannot support most aquatic life are termed “dead lakes.” The degree of negative effects due to acid rain can vary significantly. Some forests, streams, and lakes that experience acid rain do not suffer many negative effects because the alkaline soil in those areas neutralize the acidity in the rainwater. This “buffering” capacity depends on the thickness and composition of the soil and the type of rock underneath it. Effects of Acid Rain on Plant Life Forests are being killed by acid rain. Some problems are directly created by acid deposits on leaves; however, the greater problem appears to be the effects of acid deposits on the soil. Nutrients normally dissolved and used by tree roots have either been leached away or lost, or toxic quantities of other materials have been taken into solution by acidic groundwater. These materials interfere with a plant’s ability to acquire proper nourishment. The result is that plants weaken and die. These effects impact all plant life, not just the forests. Effects of Acid Rain on Human Health Direct contact with acid rain will not cause injury to humans. However, being exposed to the particulates that cause acid rain can present a health hazard. Particulates which trap SOX and NOX can be inhaled by humans. This can cause health problems such as emphysema and bronchitis. These are serious conditions. Many people are hospitalized every year and some of them die. Reducing the amount of these toxic particulates reduces the harm to humans and improves the quality of life for those with breathing ailments. Effects of Acid Rain on Buildings, Structures, and Vehicles Acid rain affects buildings and other structures, which leads to increased maintenance costs. This is especially true in buildings made of limestone or marble that contain calcium carbonate or calcium-based compounds. These are quite reactive with water in highly acidic conditions. Structures with exposed metals are also susceptible to the corrosive action of acid rain. Acid rain effects buildings and other structures, leading to increased maintenance costs. This is especially true in buildings made of limestone or marble which contain calcium carbonate or calciumbased compounds which are quite reactive with water in highly acidic conditions. Structures with exposed metals, such as copper, zinc, nickel and certain types of steel are also susceptible to the corrosive action of acid rain. To reduce damage to building structures and vehicles, acid-resistant paints are often used. 4th Class Edition 3 • Part A 2-15