Appendix B
Estimates of Signals Created in the Atmosphere by Emissions

To determine how well national emissions can be quantified from atmospheric measurements, it is necessary to first estimate the mole fraction signals produced over a country by its emissions, then compare the result to technical capabilities. The average emissions are defined as the total national emissions divided by the area, and they are expressed in units of moles per square meter per second (mol m–2 s–1). An air mass with a certain thickness, traveling over a region, collects emissions during its transit. The transit time is estimated as the fetch divided by the wind speed. The fetch is taken as the square root of the area, and a wind speed of 5 m s–1 is assumed. When trace gas emissions are mixed into the air mass, its mole fraction changes (denoted by ); the change is smaller when the trace gas is diluted into a larger air mass. The latter is expressed as moles per square meter in the column of air into which the trace is being mixed (equation 1).

(1)

At sea level the total atmospheric column contains ~356,000 mol m–2 of air. The lowest 1 km, a typical height of the atmospheric boundary layer, contains ~40,000 mol m–2 of air at sea level, or ~11 percent of the total atmosphere. In Table B.1 the total column and the boundary layer masses assume the surface to be sea level for each country. At an average wind speed of 5 m s–1, air moves 430 km in 24 hours, so it takes 4.6 days to traverse a fetch of 2,000 km. Air usually remains in the boundary layer 3-5 days. For longer fetches it becomes increasingly unlikely that all of the emissions remain confined to the boundary layer, and the mole fraction change is then overestimated for those cases.

Table B.1 compares national carbon dioxide (CO2) emissions and the estimated atmospheric signal for the 20 largest CO2-emitting nations, which represent more than 80 percent of estimated global emissions. The numbers in the last two columns are typical, but will vary greatly in practice because they are inversely proportional to wind speed. How do the estimates in Table B.1 compare with observations? Based on a very limited number of 14C measurements of CO2 in small aircraft off the coast of Cape May and New Hampshire, the average component of CO2 from recent fossil-fuel combustion is ~3 parts per million (ppm) in the boundary layer.

It is striking to note in Table B.1 how small, relative to background, the mole fraction signals are when averaged over an entire country, and also that the signals for Japan, Germany, and Korea are comparable to those for the two largest emitters: the United States and China. That is due to the higher emissions intensity (per square meter) in the three smaller countries.

Table B.2 presents data from the same 20 countries, for methane (CH4), nitrous oxide (N2O), and sulfur hexafluoride (SF6), estimated in the same way as in Table B.1. When comparing these estimates with U.S. observations from the National Oceanic and Atmospheric Administration network, the estimated



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 89
Appendix B Estimates of Signals Created in the Atmosphere by Emissions T s–1, air moves 430 km in 24 hours, so it takes 4.6 days to o determine how well national emissions can be quantified from atmospheric measurements, it traverse a fetch of 2,000 km. Air usually remains in the is necessary to first estimate the mole fraction boundary layer 3-5 days. For longer fetches it becomes signals produced over a country by its emissions, then increasingly unlikely that all of the emissions remain compare the result to technical capabilities. The average confined to the boundary layer, and the mole fraction emissions are defined as the total national emissions change is then overestimated for those cases. divided by the area, and they are expressed in units of Table B.1 compares national carbon dioxide (CO2) moles per square meter per second (mol m–2 s–1). An air emissions and the estimated atmospheric signal for mass with a certain thickness, traveling over a region, the 20 largest CO2-emitting nations, which represent collects emissions during its transit. The transit time is more than 80 percent of estimated global emissions. estimated as the fetch divided by the wind speed. The The numbers in the last two columns are typical, but fetch is taken as the square root of the area, and a wind will vary greatly in practice because they are inversely speed of 5 m s–1 is assumed. When trace gas emissions proportional to wind speed. How do the estimates in are mixed into the air mass, its mole fraction changes Table B.1 compare with observations? Based on a very (denoted by ∆); the change is smaller when the trace gas limited number of 14C measurements of CO2 in small is diluted into a larger air mass. The latter is expressed aircraft off the coast of Cape May and New Hampshire, as moles per square meter in the column of air into the average component of CO2 from recent fossil-fuel which the trace is being mixed (equation 1). combustion is ~3 parts per million (ppm) in the bound- ary layer. )× ) × fetch ( ( It is striking to note in Table B.1 how small, relative emissions mol s −1 area to background, the mole fraction signals are when aver- area wind speed aged over an entire country, and also that the signals for Japan, Germany, and Korea are comparable to those for 1 = ∆ ( drymole fraction ) the two largest emitters: the United States and China. mol m −2 (1) That is due to the higher emissions intensity (per square meter) in the three smaller countries. At sea level the total atmospheric column contains Table B.2 presents data from the same 20 coun- ~356,000 mol m–2 of air. The lowest 1 km, a typical tries, for methane (CH4), nitrous oxide (N2O), and height of the atmospheric boundary layer, contains sulfur hexafluoride (SF6), estimated in the same way ~40,000 mol m–2 of air at sea level, or ~11 percent of as in Table B.1. When comparing these estimates the total atmosphere. In Table B.1 the total column and with U.S. observations from the National Oceanic and the boundary layer masses assume the surface to be sea Atmospheric Administration network, the estimated level for each country. At an average wind speed of 5 m 

OCR for page 89
0 APPENDIX B TABLE B.1 National CO2 Emissions and Estimated Atmospheric Signal Area Fetch CO2 Population Average Emissions Total Column Boundary Layer 1 km (µmol m–2 s–1) Country (1,000 km2) (km) (Mton yr–1) (millions) (ppm) (ppm) United States 9,827 3,134 5,892 307.0 0.432 0.76 6.8 China 9,571 3,093 5,577 1,329.0 0.420 0.73 6.5 Russia 17,075 4,132 1,568 142.0 0.066 0.15 1.4 Japan 378 614 1,249 128.0 2.379 0.82 7.3 India 3,166 1,779 1,222 1169.0 0.278 0.28 2.5 Germany 357 597 829 82.6 1.672 0.56 5.0 Canada 9,985 3,159 559 32.8 0.040 0.07 0.6 UK 244 493 539 60.8 1.591 0.44 3.9 Italy 301 548 477 58.9 1.141 0.35 3.1 South Korea 99 314 475 48.2 3.455 0.61 5.4 Iran 1,648 1,283 447 71.2 0.195 0.14 1.3 Mexico 1,964 1,401 411 106.5 0.151 0.12 1.1 France 544 737 399 61.6 0.528 0.22 1.9 Australia 7,682 2,771 382 20.7 0.036 0.06 0.5 Indonesia 1,905 1,380 367 232.0 0.139 0.11 1.0 Spain 506 711 367 44.3 0.522 0.21 1.9 Brazil 8,547 2,923 352 192.0 0.030 0.05 0.4 South Africa 1,219 1,104 337 48.6 0.199 0.12 1.1 Saudi Arabia 2,240 1,496 333 24.8 0.107 0.09 0.8 Ukraine 604 777 303 46.2 0.361 0.16 1.4 NOTES: Mton CO2 = million metric ton of CO2. The totals include electricity generation, heating, transportation, manufacturing and construction, and other fuel combustion, but not bunker fuels, land-use change, or waste. SOURCES: National totals for 2005 from the World Resources Institute. Area and population are from the CIA Fact book. TABLE B.2 National Emissions of CH4, N2O, and SF6 and Estimated Atmospheric Signals CH4 N 2O SF6 Average Total Boundary Average Total Boundary Average Total Boundary Emissions (nmol Column Layer 1 Emissions (pmol Column Layer 1 Emissions (fmol Column Layer 1 Country (Mton yr–1) m–2 s–1) (ppb) km (ppb) (Mton yr–1) m–2 s–1) (ppb) km (ppb) (ton yr–1) m–2 s–1) (ppt) km (ppt) United States 20.84 4.20 7.4 65 1.261 92 0.163 1.4 842 18.60 0.0327 0.29 China 34.13 7.06 12.3 109 2.296 172 0.300 2.7 364 8.25 0.0143 0.13 Russia 12.58 1.46 3.4 30 0.193 8 0.019 0.2 175 2.22 0.0052 0.05 Japan 0.84 4.40 1.5 13 0.119 226 0.078 0.7 57 32.73 0.0113 0.10 India 21.91 13.70 13.7 121 0.239 54 0.054 0.5 92 6.31 0.0063 0.06 Germany 2.74 15.20 5.1 45 0.213 429 0.144 1.3 35 21.28 0.0071 0.06 Canada 4.08 0.81 1.4 12 0.194 13 0.025 0.2 110 2.39 0.0042 0.04 UK 1.85 15.01 4.2 37 0.153 451 0.125 1.1 22 19.57 0.0054 0.05 Italy 1.38 9.08 2.8 24 0.150 358 0.111 1.0 18 12.98 0.0040 0.04 South Korea 1.34 26.80 4.7 42 0.057 414 0.073 0.7 96 210.45 0.0372 0.33 Iran 3.83 4.60 3.3 29 0.077 33 0.024 0.2 22 2.90 0.0021 0.02 Mexico 7.39 7.45 5.9 52 0.090 32 0.026 0.2 35 3.87 0.0030 0.03 France 2.44 8.88 3.7 32 0.268 354 0.147 1.3 18 7.18 0.0030 0.03 Australia 5.16 1.33 2.1 18 0.107 10 0.016 0.1 31 0.88 0.0014 0.01 Indonesia 7.32 7.61 5.9 52 0.142 53 0.042 0.4 18 2.05 0.0016 0.01 Spain 1.46 5.71 2.3 20 0.097 138 0.055 0.5 9 3.86 0.0015 0.01 Brazil 15.56 3.61 5.9 52 0.888 74 0.123 1.1 75 1.90 0.0031 0.03 South Africa 2.21 3.59 2.2 19 0.078 46 0.029 0.3 35 6.23 0.0039 0.03 Saudi Arabia 1.11 0.98 0.8 7 0.038 12 0.010 0.1 22 2.13 0.0018 0.02 Ukraine 6.14 20.13 8.8 78 0.091 108 0.047 0.4 31 11.14 0.0049 0.04 NOTES: nmol = nanomol, 10–9 mol; pmol = picomol, 10–12 mol; fmol = femtomol, 10–15 mol. SOURCE: National emissions for 2005 from the World Resources Institute.

OCR for page 89
 APPENDIX B enhancement of greenhouse gas mole fractions is not by mountains on three sides, the residence time over far from, but on the high side of, observed values for the city is much longer. the lowest 1 km, consistent with the fact that over long fetches the emissions tend not to remain confined to SIGNAL FROM A 1 GW(E) COAL FIRED the boundary layer. For CH4, the observed annual aver- POWER PLANT age enhancement in the boundary layer of the United One gigawatt (GW) corresponds to 8.76 109 kWh States, relative to background values, is 20-60 parts per yr–1. Applying the U.S. average 25 mol C kWh–1, the billion (ppb), with large standard deviation of midday plant would produce 2.19 1011 mol yr–1, or 6,900 mol means of 20-30 ppb. For N2O, these numbers are 0.2- s–1. If the perpendicular distance across the plume is 1.7 0.4 ppb, and daily standard deviation of 0.3-0.7 ppb; for SF6, the average enhancement is 0.05-0.2 parts per km at some distance downwind, and the wind speed is 5 m s–1, then 1 second of CO2 emissions is diluted trillion (ppt), with daily variability of 0.07 to 0.13 ppt. into 1,700 × 5 m2 s–1 × 3.56 105 mol of air per square For N2O, the highest observed enhancement is 0.7 ppb over Iowa, which is indicative of intense regional meter (full atmospheric column). The number 1.7 km is chosen to correspond to the 3 km2 footprint of a single emissions. The World Meteorological Organization- recommended accuracies for in situ measurements are 2 Orbiting Carbon Observatory (OCO) sounding. The ppb for CH4, 0.1 ppb for N2O, and 0.02 ppt for SF6. CO2 increase in the total column is then 2.3 ppm. Table B.3 explores expected enhancements of the CO2 mole fraction over metropolitan areas. The signal SIGNAL FROM A GEOLOGICAL expected to be produced over a single large city rela- SEQUESTRATION LEAK tive to its surroundings is comparable to, and in many cases larger than, the average produced by an entire Significant quantities of CO2 may one day be cap- country. Note that the observed average fossil-fuel CO2 tured at large point sources in the utility and industrial enhancement at the surface in Los Angeles based on sectors and injected into storage sites in the Earth, 14C measurements of plants (Figure 4.5) is about five rather than released to the atmosphere. If this occurs, times larger over part of the basin than the number it will be important to monitor both the quantity of estimated in Table B.3. CO2 that is injected into storage sites and the amount The latter is derived with a standard assumption of of any CO2 that leaks from these sites (IPCC, 2005). a steady 5 m s–1 average wind vector, which would imply Leaks from geological sequestration are relatively easy that the residence time of air over the metropolitan area to detect. The emissions are at the surface and are not would be ~4 hours. Because Los Angeles is surrounded buoyant like those from a power plant. At night they TABLE B.3 Expected CO2 Signals for Selected Metropolitan Areas Area Emissions Emissions Total Column Boundary Layer 1 km (µmol m–2 s–1) City (km2)a (Mton CO2 yr–1) (ppm) (ppm) Los Angeles 3,700 73.2 14.2 0.49 4.3 Chicago 2,800 79.1 20.3 0.60 5.4 Houston 3,300 101.8 22.2 0.72 6.4 Indianapolis 900 20.1 16.1 0.27 2.4 Tokyo 1,700 64 27 0.63 5.6 Seoul 600 43 52 0.71 6.3 Beijing 800 74 67 1.1 9.4 Shanghai 700 112 116 1.8 15 NOTES: Mton CO2 is million metric tons of CO2. aArea represents the contiguous area of intense and activity and was estimated using Google maps in “satellite” mode, which shows built up areas by color and road density. SOURCES: Emissions in 1998 for four east Asian cities from Dhakal et al. (2003). U.S. estimates are from the VULCAN emissions inventory for 2002 ().

OCR for page 89
 APPENDIX B will tend to stay at the surface. Assume that the CO2 high, eventually depriving the vegetation of sufficient from a 1 GW(e) power plant is captured and injected oxygen in the root zone and leading to plant death, into a well. If 0.1 percent escapes during the injection, which should be easily detectable. there would be a point source of 6.9 mol s–1 of CO2. At a point 1 km downstream, with a wind speed of 5 m s–1 REFERENCES and a plume width of 100 m and plume height of 100 Dhakal, S., S. Kaneko, and H. Imura, 2003, CO2 emissions from m, the CO2 enhancement would be 3.3 ppm, causing energy use in East-Asian mega-cities, in P roceedings of the In- a 14C depletion of 0.89 percent. A second scenario is ternational Workshop on Policy Integration Towards Sustainable escape from the geological formation into which the Urban Use for Cities in Asia, February 4-5, East-West Center, CO2 has been stored. If 0.2 percent of the sequestered Honolulu, Hawaii, available at . CO2 escapes per year (residence time 500 years), the IPCC (Intergovernmental Panel on Climate Change), 2005, Carbon leak would increase over time as more CO2 is pumped Dioxide Capture and Storage, IPCC Special Report, prepared by into the formation. After 1 year the leak rate would Working Group III of the Intergovernmental Panel on Climate Change, B. Metz, O. Davidson, H.C. de Coninck, M. Loos, be 14 mol s–1, after 2 years 28 mol s–1, and so on. In and L.A. Meyer, eds., Cambridge University Press, New York, addition, when the escaping CO2 goes through soil, 442 pp. the CO2 mole fraction in soil air would become very