Download chem of carbon and GWPS 2010

GEOL 412 – Climate Change: Past, Present and Future
The Chemistry of Carbon and Global Warming Potentials
Dr. Erik Krogh, Department of Chemistry; [email protected]; 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.
http://www.kcvs.ca/site/projects/climate.html
GEOL 412 – Climate Change: Past, Present and Future
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 CO2. 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 t1/2 = 0.693 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; ax 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. CO2). 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
Radiative
Lifetime
Efficiency
(yrs)
(W m-2 ppb-1)
CO2
CH4
N2O
SF6
HFC-23
(CHF3)
1
-5
12
114
3200
270
1.4 x 10
3.7 x 10-4
3.0 x 10-3
0.52
0.19
GWP
GWP
GWP
20 year
1
70
290
16,000
12,000
100 year
1
25
300
22,800
14,800
500 year
1
7.6
153
32,600
12,200
Intergovernmental Panel on Climate Change, Third Assessment Report, 2001
http://www.grida.no/climate/ipcc_tar/wg1/247.htm, accessed Sept 16, 2008
GEOL 412 – Climate Change: Past, Present and Future
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
% mass of carbon in gasoline
Distance driven by average NA automobile
~ 0.75 kg/L
~ 85%
20,000 km/yr
GEOL 412 – Climate Change: Past, Present and Future
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 CO2.
The current costs of CCS are estimated by the Norwegian state oil company
(StatoilHydro) to be roughly $300/ton of CO2 at their Mongstad plant set to go into full
operation in 2012. Economists estimate costs of CCS will drop to between $50 – 100/ton
CO2 with efficiencies of scale and new technologies over the next decade.
GEOL 412 – Climate Change: Past, Present and Future
Exercise 3: Altering the Earth’s Atmosphere by Burning Fossil Fuels2
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 CO2 and with the
hydrogen to make H2O. The Earth’s atmosphere contains about 1.8 x 1020 moles of air,
of which about 7.0 x 1014 moles are CO2 (using the current atmospheric concentration of
390 ppmv, i.e., 390 x 10-6 x 1.8 x 1018). Information about the average chemical
composition and energy content of the three fossil fuels and global consumption rates are
summarized below.
Average
composition
Petroleum
Natural Gas
Coal
CH1.5
CH3.6
CH0.8
Percent
combustible
of total
98% (w/w)
88% (v/v)
75% (w/w)
Worldwide
consumption
1980 (x 1018 J/yr)
135
60
90
Energy content
43 x 106 J/kg
3.9 x 107 J/m3 (STP)
29.3 x 106 J/kg
In 1980, how much O2 was removed from the atmosphere due to the combustion of fossil
fuels on Earth and how much CO2 and H2O were produced in the combustion process?
If all the CO2 released to the atmosphere in 1980 from fossil-fuel burning remained there,
by what percentage would it increase the 1980 atmospheric concentration of 340 ppmv?
Update your answer using current fossil fuel consumption estimates.
It turns out that H2O is a more effective absorber of infrared radiation than is CO2. Given
that the emissions of H2O were comparable to those of CO2, why is there less concern
about the effect of H2O emissions on the radiative balance in the atmosphere?
Rank these fossil fuels based on the mass of CO2 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.
GEOL 412 – Climate Change: Past, Present and Future
Exercise 4: Atmospheric CO2 and the Ocean Sink
Background: Prior to the industrial revolution in 1800, the concentration of CO2 in the
atmosphere was about 270 ppmv. Because the atmosphere contains 1.8 x 1020 moles of
air, there were about 270 x 10-6 x 1.8 x 1020 or 4.9 x 1016 moles of CO2 in the atmosphere
at that time. The concentration of CO2 in the atmosphere in 1980 was about 340 ppmv,
corresponding to 6.1 x 1016 moles of CO2 – a gain of 1.2 x 1016 moles. The total CO2
injected into the atmosphere between 1800 and 1980 is estimated to be about 1.6 x 1016
moles. Therefore, 1.2/1.6, or ~75% of the CO2 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 CO2 into the ocean?
As more CO2 is dissolved in seawater, what is the predicted effect on the pH of the ocean
and the solubility of CaCO3 and other carbonate bearing minerals?
GEOL 412 – Climate Change: Past, Present and Future
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 gas3.
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 NF3?
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, NF3, 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.
GEOL 412 – Climate Change: Past, Present and Future
Global Warming Potentials
Reading Package for GEOL 412
Readings Included:
1. Something Nasty in the Air, New Scientist, 21 January 2006
2. CFC substitutes will still add to global warming, New Scientist, 14 April, 1990
3. TV Boom may boost Greenhouse Effect, New Scientist, 02 July 2008
4. Table 2.14 Lifetimes, Radiative efficiencies and GWPs relative to CO2,
Chapter 2, Third Assessment Report, IPCC
5. High Global Warming Potential (GWP) Gases, US EPA
http://www.epa.gov/highgwp/sources
accessed Sept 24, 2009
Further Readings:
1. M.J. Prather and J. Hsu, NF3, the greenhouse gas missing from Kyoto,
Geophysical Res. Letters, 35, L12810, 2008
2. Velders et al., The large contribution of projected HFC emissions to future
climate forcing, Proceedings of the National Academy of Science, 106, 10949,
2009
3. McKenna, Phil, Carbon Control: Turning carbon trash into treasure, New
Scientist, Sept 22, 2010
4. Collisional Heating by CO2 in the Atmosphere and Infrared Spectral Windows
http://www.kcvs.ca/site/projects/climate.html
accessed Sept 28, 2010