The Chemistry of Carbon and Global Warming Potentials Dr. Erik Krogh, Department of Chemistry; Local 2307

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1 The Chemistry of Carbon and Global Warming Potentials Dr. Erik Krogh, Department of Chemistry; Local 2307 Biogeochemical Cycling - Where on Earth is all the carbon and what s it doing there? Chemical speciation and Residence time Biogeochemical cycle of Carbon - Sources, Reservoirs, Sinks, Stocks and Fluxes The animations that Erik showed are from the King s Centre for Visualization in Science. There are some other instructive animations including one on Radiative Energy Balance and Ice-Core Analysis.

2 Global Warming Potentials (GWPs) An index developed by the IPCC (1990) 1 based on the time-integrated global mean radiative forcing of a pulse emission of some compound relative to the same mass of CO 2. GWP are calculated over a specific time interval and this value must be stated along with the GWP (typically 100 yrs) or else the number is meaningless. GWPs are a function of three intrinsic properties of a GHG; - absorption efficiency of IR radiation (extinction coefficient) - wavelength of IR radiation (relative to atmospheric IR windows) - atmospheric lifetime (τ= stock/flux and t 1/2 = τ) Global Warming Potentials (GWPs) are one type of simplified index based upon radiative properties that can be used to estimate the potential future impacts of emissions of different gases upon the climate system in a relative sense. High GWPs correlate with a strong infrared absorption coefficients in an atmospheric IR window and a long atmospheric lifetime. A gas has the most effect on GWP if it absorbs IR in a "window" of wavelengths where the atmosphere is fairly transparent. Because the GWP of a greenhouse gas depends directly on its infrared spectrum, the use of infrared spectroscopy to study greenhouse gases is centrally important in the effort to understand the impact of human activities on global climate change. The GWP is defined as the ratio of the time-integrated radiative forcing from the instantaneous release of 1 kg of a trace substance relative to that of 1 kg of a reference gas: where TH is the time horizon over which the calculation is considered; a x is the radiative efficiency due to a unit increase in atmospheric abundance of the substance (i.e., Wm -2 kg -1 ) and [x(t)] is the time-dependent decay in abundance of the substance following an instantaneous release of it at time t=0. The denominator contains the corresponding quantities for the reference gas (i.e. CO 2 ). Note that a substance's GWP depends on the timespan over which the potential is calculated. A gas which is quickly removed from the atmosphere may initially have a large effect but for longer time periods as it has been removed becomes less important (see further GWP vales for methane and sulfur hexafluoride over 20 and 100 yr time horizons). Atmospheric Lifetime (yrs) Radiative Efficiency (W m -2 ppb -1 ) GWP GWP GWP 20 year 100 year 500 year CO x CH x N 2 O x SF ,000 22,800 32,600 HFC-23 (CHF 3 ) ,000 14,800 12,200 1 Intergovernmental Panel on Climate Change, Third Assessment Report, accessed Sept 16, 2008

3 Problem Exercises Exercise 1: Carbon Savings in Fuel Efficiency Estimate the mass of carbon dioxide prevented from entering the atmosphere per year year for an automobile rated at 9.2 L/100 km (30 mpg) versus one rated at 14 L/100 km (20 mpg). If the cost of removing carbon dioxide from the atmosphere is estimated to be $200/tonne, estimate the added hidden cost of the less efficient vehicle over a ten year life cycle. Information for Exercises 1 and 2 Density of gasoline ~ 0.75 kg/l % mass of carbon in gasoline ~ 85% Distance driven by average NA automobile 20,000 km/yr

4 Exercise 2: Adjusted Price at the Pump Estimate the adjusted price to a liter of gasoline to offset the cost associated with carbon capture and sequestration (CCS) at $200/ton of CO 2. The current costs of CCS are estimated by the Norwegian state oil company (StatoilHydro) to be roughly $300/ton of CO 2 at their Mongstad plant set to go into full operation in Economists estimate costs of CCS will drop to between $50 100/ton CO 2 with efficiencies of scale and new technologies over the next decade.

5 Exercise 3: Altering the Earth s Atmosphere by Burning Fossil Fuels 2 Background: The primary constituents of the three major types of fossil fuels (natural gas, petroleum and coal) are carbon and hydrogen. When fossil fuel is burned, the oxygen from the atmosphere combines with the carbon to make CO 2 and with the hydrogen to make H 2 O. The Earth s atmosphere contains about 1.8 x moles of air, of which about 7.0 x moles are CO 2 (using the current atmospheric concentration of 390 ppm v, i.e., 390 x 10-6 x 1.8 x ). Information about the average chemical composition and energy content of the three fossil fuels and global consumption rates are summarized below. Average composition Percent combustible of total Worldwide consumption 1980 (x J/yr) Energy content Petroleum CH % (w/w) x 10 6 J/kg Natural Gas CH % (v/v) x 10 7 J/m 3 (STP) Coal CH % (w/w) x 10 6 J/kg In 1980, how much O 2 was removed from the atmosphere due to the combustion of fossil fuels on Earth and how much CO 2 and H 2 O were produced in the combustion process? If all the CO 2 released to the atmosphere in 1980 from fossil-fuel burning remained there, by what percentage would it increase the 1980 atmospheric concentration of 340 ppm v? Update your answer using current fossil fuel consumption estimates. It turns out that H 2 O is a more effective absorber of infrared radiation than is CO 2. Given that the emissions of H 2 O were comparable to those of CO 2, why is there less concern about the effect of H 2 O emissions on the radiative balance in the atmosphere? Rank these fossil fuels based on the mass of CO 2 released per Joule of energy produced. 2 Exercise 3 and 4 adapted from Consider a Spherical Cow: A Course in Environmental Problem Solving, John Harte, University Science Books, Mill Valley, CA, 1988.

6 Exercise 4: Atmospheric CO 2 and the Ocean Sink Background: Prior to the industrial revolution in 1800, the concentration of CO 2 in the atmosphere was about 270 ppm v. Because the atmosphere contains 1.8 x moles of air, there were about 270 x 10-6 x 1.8 x or 4.9 x moles of CO 2 in the atmosphere at that time. The concentration of CO 2 in the atmosphere in 1980 was about 340 ppm v, corresponding to 6.1 x moles of CO 2 a gain of 1.2 x moles. The total CO 2 injected into the atmosphere between 1800 and 1980 is estimated to be about 1.6 x moles. Therefore, 1.2/1.6, or ~75% of the CO 2 originally injected from burning fossil fuels remained present in the atmosphere. A likely possibility is that the oceans have taken up most of the remaining 25%. Using the information in the figure of the carbon cycle, how much more inorganic carbon is present in the Earth s oceans than the atmosphere? What chemical processes are involved in the net flux of atmospheric CO 2 into the ocean? As more CO 2 is dissolved in seawater, what is the predicted effect on the ph of the ocean and the solubility of CaCO 3 and other carbonate bearing minerals?

7 Exercise 5: Assessing the Global Warming Potential of new atmospheric pollutants. Background: It has recently been suggested that nitrogen trifluoride a solvent used in the manufacture of new LCD televisions has significant contributions as a greenhouse gas 3. The global warming potential (GWP) of an atmospheric gas is a measure of its radiative contribution (W m -2 kg -1 ) to global warming relative to that of carbon dioxide. A GWP is calculated over a specific time interval (which must be stated). What information would you need to estimate the global warming potential of NF 3? How would you go about finding this information? What other information is relevant to determine if this gas makes a significant contribution to global warming? 3 For more information of this issue see M.J. Prather and J. Hsu, NF 3, the greenhouse gas missing from Kyoto, Geophysical Res. Letters, 35, L12810, 2008 and Velders et al., The large contribution of projected HFC emissions to future climate forcing, Proceedings of the National Academy of Science, 106, 10949, 2009.

8 Global Warming Potentials Reading Package for GEOL 412 Readings Included: 1. Something Nasty in the Air, New Scientist, 21 January CFC substitutes will still add to global warming, New Scientist, 14 April, TV Boom may boost Greenhouse Effect, New Scientist, 02 July Table 2.14 Lifetimes, Radiative efficiencies and GWPs relative to CO 2, Chapter 2, Third Assessment Report, IPCC 5. High Global Warming Potential (GWP) Gases, US EPA accessed Sept 24, 2009 Further Readings: 1. M.J. Prather and J. Hsu, NF 3, the greenhouse gas missing from Kyoto, Geophysical Res. Letters, 35, L12810, Velders et al., The large contribution of projected HFC emissions to future climate forcing, Proceedings of the National Academy of Science, 106, 10949, McKenna, Phil, Carbon Control: Turning carbon trash into treasure, New Scientist, Sept 22, Collisional Heating by CO 2 in the Atmosphere and Infrared Spectral Windows accessed Sept 28, 2010