Carbon dioxide atmospheric residence time

This is a contentious figure because of its potential significance in climate change model predictions. In the literature a variety of values are quoted Cawley GC (2011) On the atmospheric residence time of anthropogenically sourced carbon dioxide. Energy Fuels 25 5503-5513... 

The results are shown in Figure 2-3, in which the solid line is the exact solution. This numerical approach shows no sign of instability even for a time step of 40 years, nearly five times larger than the residence time of atmospheric carbon dioxide (distime). In fact, the reverse Euler method is nearly always stable, and so I shall use it from now on. 

Catalytic tests of n-pentane oxidation were carried out in a laboratory glass flow-reactor, operating at atmospheric pressure, and loading 3 g of catalyst diluted with inert material. Feed composition was 1 mol% n-pentane in air residence time was 2 g s/ml. The temperature of reaction was varied from 340 to 420°C. The products were collected and analyzed by means of gas chromatography. A FlP-l column (FID) was used for the separation of C5 hydrocarbons, MA and PA. A Carbosieve Sll column (TCD) was used for the separation of oxygen, carbon monoxide and carbon dioxide. 

From Figure 9.1, it can be seen that the major form of carbon in the atmosphere is C02(g), constituting over 99% of atmospheric carbon. Carbon dioxide makes up 0.035% by volume of atmospheric gases, or 350 ixatm = 350 ppmv. The atmosphere has a mass of CO2 that is only 2% of the mass of total inorganic carbon in the ocean, and both of these carbon masses are small compared to the mass of carbon tied up in sediments and sedimentary rocks. Therefore, small changes in carbon masses in the ocean and sediment reservoirs can substantially alter the CO2 concentration of the atmosphere. Furthermore, there is presently 3 to 4 times more carbon stored on land in living plants and humus than resides in the atmosphere. A decrease in the size of the terrestrial organic carbon reservoir of only 0.1% y-1 would be equivalent to an increase in the annual respiration and decay carbon flux to the atmosphere of nearly 4%. If this carbon were stored in the atmosphere, atmospheric CO2 would increase by 0.4%, or about 1 ppmv y-l. The... 

Carbon dioxide is chemically stable and has an average residence time in the atmosphere of about four years before it enters either the oceans or terrestrial ecosystems. 

The principal components of the atmosphere are nitrogen 78.09%, oxygen 20.95%, argon 0.932%, and carbon dioxide 0.03% (vol%, dry atmospheric air). The water content varies from 0.1 to 2.8vol%. However, there are some other components which in spite of their low concentrations exert strong influence on atmospheric chemistry [4]. Table 1 shows the natural content (i.e. average stationary concentrations) of the principal trace components, their average lifespans and rates of supply and removal from the atmosphere. Two latter values are equal to each other and are calculated as the ratio of the stationary concentration of an atmospheric component to its residence time in the atmosphere. 

It can be seen that the great majority of carbon is cycled in the atmosphere as carbon dioxide. Thus, although the oxidation of CO provides an important sink, the process does not supply an important C02 source. It follows from the data given that the residence times of methane, carbon monoxide and carbon dioxide are 5.0 0.25 and 5.2 years, respectively. 

The residence time of CO2 in the atmosphere is about two years, which makes the atmospheric air quite well mixed with respect to this gas. However, a more recent analysis shows that the terrestrial ecosystems have much stronger sinks of carbon dioxide uptake. The details of major ecosystem-level CO2 experiments have been shown recently (Koch and Mooney, 1996). 

Like methane and nitrous oxide, tropospheric ozone is a natural greenhouse gas, but one which has a short tropospheric residence time. Ozone s bending vibration occurs at 14.2 pm, near that for CO2, and thus it does not contribute much to the enhancement of the greenhouse effect since atmospheric carbon dioxide already removes much of the outgoing light in this wavelength. 

In addition to the biological factors noted above, the isotopic composition of inorganic carbon is influenced by the exchange of carbon between surface waters and the atmosphere. Carbon isotopes are fractionated with the transfer of carbon between water and the atmosphere (Siegenthaler and Munnich 1981 Zhang et al. 1995), with equilibrium fractionation resulting in atmospheric carbon dioxide about 8%o depleted relative to the ocean. This effect is temperature dependent, with a change in fractionation of approximately -0.1%o per K (Mook 1986). Thus, at equilibrium, DIC in colder waters is enriched in C relative to warmer waters. In natural waters, the time required for isotopic equilibration is slow relative to the residence time of carbon in surface waters... 

Carbon dioxide is removed from the atmosphere by photosynthesis in green piants and soiution in aquatic systems like this marsh its average residence time in the atmosphere is about 100 years. (Jaap Hart/iStockphoto)... 

Natural occurrence. Carbon dioxide which is present in the atmosphere at roughly 380 ppm vol. is produced by respiration and by combustion and it is consumed by plants during photosynthesis. Exhaled air contains as much as 4 vol.% carbon dioxide. However, it has a short residence time in this phase. The oceans hold much of the Earth s total inventory of carbon dioxide. 

In the ocean, elements that form insoluble hydroxides have relatively short residence times (e.g., A1 and Fe have residence times in the ocean of 100 and 200 years, respectively). Cations, such as Na (aq) and K (aq), and anions, such as Cl (aq) and Br (aq), have longer residence times in the ocean ( 7 x 10 to 10 years). In the atmosphere, the very stable gas nitrogen has a residence time of a million years or so, while oxygen has a residence time of 5,000-10,000 years. Sulfur dioxide, water, and carbon dioxide, on the other hand, have residence times in the atmosphere of only a few days, 10 days, and 4 years, respectively. Of course, residence times may be determined by physical removal processes (e.g., scavenging by precipitation) as well as chemical. 

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