Environment & Energy

Environmental effectsValentim M B Nunes

Unidade Departamental de Engenharias

Instituto Politécnico de Tomar, March, 2015

IntroductionThe production and consumption of virtually all types of energy have environmental impacts. The use of fossil fuels contributes to the accumulation of CO2 that is the main greenhouse gas. Deforestation also contributes to this effect because the forest is a carbon sink.

The accelerated industrialization in the 20th Century (even more than the population growth) came to bring humanity new problems and challenges: in one hand the growing energy consumption is a reality, on the other the impacts are important, such as global warming, the depletion of the ozone layer or the problem of acid rain…

Great challenge of the 21th century: Energetic issues vs Environment!

Types of production and impact

Hydroelectric power station: causes the flooding of large areas, with consequent modification of wild fauna and flora, and the flooding of cities, causing the displacement of populations. In addition to that, the eventual misuse of water, which is a multiple use, and the possibility of methane gas emissions, by organic decomposition generated by flooding.

Thermoelectric Power station: the burning of fossil fuels for electricity production originates CO2, exacerbating the greenhouse effect and global warming. Also causes contamination of the atmosphere, soil and water through the ashes swept away by the flow of gas. In addition, nitrogen oxides and sulfur can cause lung problems, cardiovascular and kidney of populations residing in the vicinity and contribute to acid rain.

Nuclear Power Plant: it involves the vital issues of security and the treatment of nuclear waste, and has an important negative factor of rising the temperature of watercourses used in refrigeration, damaging local biodiversity.

Wind power: produces high level of noise pollution, causing changes in audition in the nearby population.

Oceanic and Geothermal: can change local food chains, damaging flora and fauna.

Global WarmingGlobal warming is the increase in the average temperature of the oceans and the air near the Earth's surface that occurs since the mid-twentieth century and which will continue in the 21st century. According to the fourth assessment report of the Intergovernmental Panel on climate change (2007), the temperature on the Earth's surface rose 0.74 ± 0.18 °C during the 20th century. Most of the observed temperature increase since the middle of the 20th century was caused by increasing concentrations of greenhouse gases, as a result of human activities such as burning fossil fuels and deforestation.

Carbon dioxide and other greenhouse gases warm the atmosphere preventing heat transfer by radiation from the Earth into outer space. Limiting the growth of the amount of CO2 in the atmosphere of the Earth requires: (a) reducing the amount of fossil fuels burned; (b) sequestration of CO2 below the surface of the Earth or the oceans.

Ozone layer

MAIN RESPONSIBLE FOR THE REDUCTION OF THE OZONE LAYERPollutant Sources

At the national level stand out, for its emissions, industrial and production units of energy as electric power generation, refineries, pulp mills, steel, cement and chemical industry in general. The use of fuels for energy production is one of the major factors.

This layer is critical to ensure life on Earth, since stratospheric ozone has the ability to absorb much of the ultraviolet radiation that can cause harmful effects (or even fatal) in living things.

Acid Rain

The burning of coal and fossil fuels and industrial pollutants released sulfur and nitrogen dioxide in the atmosphere. These gases combine with hydrogen present in the atmosphere in the form of water vapor. The result is acid rain.

The main cause of acidification is the presence in the atmosphere of gases and particles rich in reactive sulfur and nitrogen whose hydrolysis in the middle atmosphere produces strong acids. Of particular importance the nitrogen compounds (NOx) generated by high temperatures from burning of fossil fuels and the sulphur compounds (SOx) produced by the oxidation of sulphur impurities existing in most coals and petroleum.

The Kyoto Protocol

This Protocol was adopted in 1998 in Kyoto, Japan. Requires participating countries to reduce anthropogenic emissions of greenhouse gases (CO2, CH4, N2O, HFCs, PFCs, and SF6) to at least 5% values below 1990 levels during the period 2008 to 2012.

The Protocol encourages signatory countries to cooperate among themselves, through some basic actions:

Reforming the energy and transport sectors;Promote the use of renewable energy sources;Eliminate inappropriate market and financial mechanisms for the purposes of the Convention;Limit methane emissions in waste management and energy systems;Protect forests and other carbon sinks

Global warming is an enhancement of the greenhouse effect of the earth’s atmosphere, resulting in an increase of the annual average surface temperature of the earth on the order of 0.5–1 ◦C since the middle of the nineteenth century. While yet small, this temperature rise might reach 2–3 ◦C by the end of the twenty-first century, an amount believed almost certain to cause global climate changes affecting all biological life on the planet with uncertain consequences.

Most emissions of greenhouse gases and aerosols are a consequence of the use of fossil fuels, to meet the growing needs of energy. Burning 1 kg of coal releases about 3.4 kg of CO2; the burning of oil about 3.1 kg; and natural gas about 2.75 kg. In 1996 the global anthropogenic emissions of CO2 reached 25 Gton per year!

Based on the IPCC recommendations, the Framework Convention on Climate Change convened in Kyoto in late 1997 to discuss international efforts on curbing greenhouse gas emissions. The developed countries and the so-called “transition countries” (mainly the former USSR and eastern European countries) agreed that by 2010 they would reduce their CO2 emissions to an average of 6–8% below 1990 emission levels. (Because CO2 emissions in the developed countries are increasing on average by 1.5–2% per year, the emission reduction target in 2010 would be much greater than 6–8% below unconstrained 2010 levels.) Unfortunately, the lesser developed countries, including China, India, Indonesia, Mexico, and Brazil, did not sign the Kyoto agreement. Also, some developed countries, notably the United States, had not ratified the agreement by 2003.

Intergovernmental Panel on Climate Change (IPCC)

WHAT IS THE GREENHOUSE EFFECT?

The term greenhouse effect is derived by analogy to a garden greenhouse. There, a glass covered structure lets in the sun’s radiation, warming the soil and plants that grow in it, while the glass cover restricts the escape of heat into the ambient surroundings by convection and radiation. Similarly, the earth’s atmosphere lets through most of the sun’s radiation, which warms the earth’s surface, but certain gases, called greenhouse gases (GHG), trap outgoing radiative heat near the surface, causing elevated surface temperatures.The warming effect on the earth’s surface by certain gases in the atmosphere was first recognized in 1827 by Jean-Baptiste Fourier, the famous French mathematician. Around 1860, the British scientist John Tyndall measured the absorption of infrared radiation by CO2 and water vapor, and he suggested that the cause of the ice ages may be due to a decrease of atmospheric concentrations of CO2. In 1896, the Swedish scientist Svante Arrhenius estimated that doubling the concentration of CO2 in the atmosphere may lead to an increase of the earth’s surface temperature by 5–6 ◦C.

In the UV region of spectrum, oxygen and ozone in the stratosphere are the most absorbing gases. In the part of the visible, fluctuations in the density of molecules in the atmosphere reflects sunlight. In the infrared, polyatomic molecules present in the lower parts of the atmosphere (troposphere) as the H2O, CO2, O3, CH4, N2O, and other, absorb solar radiation.

500 nm

So = annual average solar energy that reaches the top of the atmosphere, known as the solar constant, 1367 W.m−2

RE = radius of Earth, 6371 kmα = current average value of terrestrial albedo, 0.3 ± 0.03

σ = Stefan–Boltzmann constant, 5.67 10−8 W m−2 K−4

TE = black body equivalent radiative temperature of the Earth, K

)1(20 ES RSI

424 EEE TRI

At present, the average temperature of the Earth's surface is TS = 288 K (15 ◦C). The difference TS − TE = 33 K is a consequence of the greenhouse effect.

The average temperature of the Earth's surface changed along the geological epoch, as is evidenced by the glacial and interglacial periods. In part, these temperature variations may have been caused by the variation of concentration of GHG in the atmosphere. Other factors to global climate change may have been related to variations in the Earth's orbit around the Sun and the tilt of its axis. At first, the eccentricity of the Earth's elliptical orbit varies over a period of about 100 000 years. This makes the average insolation of the Earth vary. Second, the axis of rotation of the Earth in relation to the elliptical orbit varies between 21.6 and 24.5° (currently 23.5°) over a period of about 41 000 years. This changes the amount of heat that strokes the hemispheres. A third possibility is a change in the solar constant.

The GHG molecules can shorten the terrestrial radiation leaving the Earth only if they are at a temperature lower than the Earth itself. We saw before that the Earth's radiative temperature corresponds to a black body temperature of 255 K. With an average surface temperature of 288 K and medium temperature gradient in the troposphere of approximately − 6 K/km, apparent height (mean radiating height), which originates a 255 K temperature is 5.5 km. Since the temperature effective radiative remains about 255 K, the addition of GHGS to the atmosphere will alter the surface temperature, TS, the profile of altitude average temperatures and radiation.

In addition to the radioactive effect due to increased GHG concentrations, modelling of global warming is more complicated because an increase in surface temperatures inevitably will cause side effects, referred to as feedback effects. This can be expressed by the proportionality:

where ΔTS is the increment in surface temperature, ΔQ is the radiative effect due simply to the GHG, and β is a factor accounting for the feedback effect. If β ˂ 1, the feedback is positive, which causes the surface temperature increase is even bigger than the due only to an increase in the concentration of greenhouse gases. If β ˃ 1, the feedback is negative, which attenuates the rise in surface temperature. There are several possible feedback effects: water vapor, clouds, aerosols, ice albedo, circulation of the oceans.

/QTS

Water vapor feedback

This mechanism is perhaps the most important in terms of feedback effects. Water vapor is a gas that absorbs strongly infrared radiation at wavelengths between 5 and 7 μm and above 10 μm. Since the average temperature of the Earth's surface rises due to increasing concentrations of greenhouse gases, more evaporation will occur from the vast areas of the oceans, the atmosphere will be more saturated in water vapor or humidity will increase. This will cause an increase in the absorption of infrared radiation that leaves Earth, and so cause a positive feedback effect. Radioactive models predict that feedback from the water can cause an increase in global warming in about 60% (β ≈ 0.6).

Cloud-Radiation Feedback

The effect of feedback of clouds is very difficult to quantify. The clouds can have a negative or positive effect. The negative effect is due to the reflection of solar radiation by clouds that arrives on Earth, contributing to an increase in the Earth's albedo and then reducing the temperature of the surface. The positive effect is due to the reflection of heat radiation that leaves the Earth. The balance of these two effects depends on the characteristics of clouds, their altitude and size of droplets or ice crystals. The modelling of these effects contains a high degree of uncertainty. Currently the best estimates point to a positive effect (the highest altitude cloud formation), in such a way that the value of β ≈ 0.8 is used to calculate the surface temperature increase due to increasing GHG concentrations.

Aerosol Feedback

As the clouds, small suspended particles (whether natural or man-made), known as aerosols, can interfere with the solar radiation that hits the Earth and terrestrial radiation. The average composition of aerosols is approximately 1/3 of dust (from soil, sand, rocks ...), 1/3 of sulphides (above all from the sulfur emissions associated with fossil fuels), and 1/3 of carbonaceous materials and nitrates (also from fossil fuels). The average diameter of the aerosol particles are less than 1 µm. This diameter is more effective at dispersing the solar radiation that hits the Earth than to reflect the terrestrial radiation. Thus, the aerosol as negative feedback, reducing the greenhouse effect in about 10-15% (β ≈ 1.1). The aerosols can have an indirect effect of feedback, serving for the condensation nuclei for clouds. This effect is very difficult to account for, and is still under study.

Ice albedo feedback

As the Earth surface rises due to increased concentration of GHG, the layers of the Arctic and Antarctic ice can melt. Also the glaciers, which are in recession during this interglacial period, can go back faster. Once the ice has a very high albedo (reflecting more sunlight) than water and earth, the disappearance of ice will cause a decrease of the total Earth albedo, α, which will cause a radiative temperature of the Earth, TE, and also the surface, TS, slightly higher. This effect may contribute to global warming more 20% (β ≈ 0.8). All together, the various effects of feedback can double the global warming caused by GHG.

Feedback from circulation of the oceans

Another possible mechanism of feedback is the change of the circulation of the oceans and ocean currents. Generally, the colder and more saline water sink to great depths, and warmer waters and less saline rise to the surface. The colder and more saline waters than average, are generated in the Arctic poles, once the ice is formed on the surface. These waters sink into the ocean and move towards the equator. There, warmer waters and less saline rise to the surface and move towards the poles. With the melting of the ice caps, and an increase of precipitation to higher latitudes, the normal pattern of circulation of the oceans can be altered, with possible consequences on global average temperature of the Earth's surface. This effect is very difficult to predict, and can be positive, negative or neutral. However the change in ocean currents may have other consequences such as El Niňo and other storms.

Effects of global warming

Rising of sea level

With the increase in the average surface temperature, the sea will rise due to three factors: melting of the ice caps, glaciers reduction and thermal expansion of ocean waters.

Kiribati, a very small country made up of 32 atolls and one island-volcano in the Pacific Ocean, wants to move to Fiji. The Beretitenti (President) is negotiating the purchase of 20 km2 in Fiji to move to there the entire population.in Public newspaper, March 10, 2012

Emission of greenhouse gasesSince carbon constitutes most of the mass of all living creatures on Earth, there is a huge reservoir of carbon in the biosphere and in the fossilized remains. The sedimentary limestone, CaCO3, contains about 12% of its mass as carbon. This limestone is originated in part from the shells and skeletons of living creatures in the past and in part by precipitation from aqueous solutions oversaturated in CaCO3. There is a continuous exchange of CO2 between the biosphere and the atmosphere. Carbon dioxide is absorbed from the atmosphere during photosynthesis of vegetation earth and and phytoplankton that live in the oceans and other water on the surface. The carbon dioxide back into the atmosphere during respiration and decomposition (slow combustion of carbonaceous materials) of dead plants and animals.

Besides CO2, contribute to global warming methane, nitrous oxide, chlorofluorocarbons (CFCs), which are products entirely produced by man, which are produced in industrial units for uses such as refrigerants, propellants, foaming agents, solvents, etc. and the ozone.In conclusion, in the year 2100, CH4, N2O, and CFCS can contribute with about 1/3 to global warming. The remaining 2/3 that are due to CO2

Carbon

At present, about 6.8 Gt.y−1 of carbon (25 Gt.y−1 of CO2) are emitted into the atmosphere due to the combustion of fossil fuels. Other 1.5 ± 1 Gt.y−1 are emiteddue to deforestation and land use change.

The reduction of CO2 emissions can be achieved by combining several approaches:

• Efficiency improvements in energy end-use.• Efficiency improvements of the energy production side.• Carbon capture and sequestration of CO2 in underground reservoirs or at the bottom of the oceans.• Use of CO2 to increase oil and gas collection and increase production (photosynthesis)• Switch to non-fossil energy sources (renewable)

Reduction of Emissions

The CO2 capture is feasible only in large power plants, especially those that burn coal (because coal emits more CO2 than oil or gas). A 1000-MW coal-emits between 6 to 8 Mt.y−1 of CO2. The capture of CO2 from all the big coal-fired power stations around the world would represent a significant reduction of global emissions. The following technologies for CO2 capture are under development:• Separation from the air, and recycling of CO2

• Solvent Absorption• Separation by membranes After the capture, the CO2 needs to be stored in reservoirs for an indefinite period, so as not to re-emerge into the atmosphere. The following reservoirs are being investigated, and in some cases are already used to storage of CO2:• Depleted oil and gas reservoirs.• Under the Oceans• Under aquifers.

Nature uses CO2 as raw material to produce biomass through photosynthesis:

nCO2 + mH2O + hν→ Cn(H2O)m + O2

Where hν represents a photon, and Cn(H2O)m is a precursor of biomass. The reaction is endothermic. This energy comes from the Sun. All vegetation and phytoplankton in the world is based on that reaction. Once the plants and plankton are at the bottom of the food chain all life on earth depends on that reaction. In fact, all fossil fuels were created by converting biomass geochemistry in coal, oil or natural gas. The use of biomass as fuel in thermal engines is neutral in terms of CO2. The use of biomass as renewable energy will be discussed later in this course.

The contribute of Nature

Problem 1Calculate the Earth's radiative temperature (K) for terrestrial albedo of α = 0.3, α = 0.27 and α = 0.33, admitting that the solar constant does not change.

Problem 2Utilizing the data of the National Aeronautics and Space AdministrationGoddard Institute for Space Studies, available in http://data.giss.nasa.gov/gistemp/graphs_v3/Fig.A2.txt , make an estimative of the increase in Earth temperature since 1950 until nowadays.

Problem 3The fraction by volume of CO2 in the atmosphere is 370 ppm. What is the carbon content (Gt) in the atmosphere if CO2 was the only carrier? The radius of the Earth is 6371 km, and the mass of the atmosphere per unit of surface area is 1,033×104 kg.m-2

rNdt

dN treNtN 0)(

,

Problem 4Current concentrations of CO2 and CH4 are 370 and 1.7 ppm, respectively. The first grows at a rate of 0.4%/y and the other 0.6%/y. What will be the concentrations of these gases in 2100. Use an exponential growth instead of linear.

Problem 5A 1000-MW power station, with a thermal efficiency of 35%, during 100% of time, uses coal with the formula CH and a calorific value of 30 MJ/kg. How much CO2 emits this unit in tones per year?

We will solve this problem in next lecture!

Bibliography

Harold H, Schobert, Energy and Society, Taylor&Francis, New York, 2002

http://www.mocho.pt/Ciencias/ambiente/chuva_acida/

G. Aubrecht, Energy, 2nd ed., Prentice Hall, New Jersey, 1994

Fay, J., Golomb, D.S., Energy and the Environment, Oxford University Press and Open University, Oxford, UK, 2004