Methane mixing ratio

Figure 5.15. Vertical distribution of the methane mixing ratio (ppmv). Observations at various latitudes and one-dimensional model calculations (from Ehhalt and Tonnissen, 1980.)...

Figure 5.16. Methane mixing ratio (ppmv) measured by HALOE (UARS) during the period 21 September-15 October 1992 and represented as a function of latitude and pressure (Russell et al, 1993).

FIGURE 2.4 Methane mixing ratios over the last 1000 years as determined from ice cores from Antarctica and Greenland (IPCC 1995). Different data points indicate different locations. Atmospheric data from Cape Grim, Tasmania, are included to demonstrate the smooth transition from ice core to atmospheric measurements. 

This you cannot do in an adiabatic reactor unless you go to extremely high mixing ratios of fresh feed and recycle gas. In summary, it is a question of selectivity, which is the reason for using the isothermal reactor for Fischer-Tropsch. An adiabatic reactor with a waste heat boiler is cheaper than an isothermal feactor, and hence it is used for methanation. 

Liquefied petroleum gas (LPG) was used as fuel for the first time in the USA in 1912. Under the general term natural gas liquids (NGL), 60% of global LPG originates as a fraction separated from methane during the production of oil and gas the remaining 40% are generated as a by-product from the fractionated distillation of crude oil in refineries. Liquefied petroleum gas is a mixture of propane and butane, with the mixing ratio dependent on the country and season. 

Breas, O., Guillou, C., Reniero, F. Wada, E. 2002. The global methane cycle Isotopes and mixing ratios, sources and sinks. Isotopes In Environmental and Health Studies, 37, 257-379. 

Bainbridge and Heidt (8) estimated from the rate of decrease of the CH mixing ratio above the tropopause that at most 10% of the tropospheric CH was lost by transport into the stratosphere and suggested that a large tropospheric sink was necessary. Ehhalt and Heidt (53) found that the calculated sink for methane due to transport into the stratosphere was much too small. 

Dhar and Ram (50) found formaldehyde in rain water and estimated a tropospheric mixing ratio of 0.7 ppb, while Cauer (36) measured a mean value of 0.4 ppb. Lodge and Pate (160) obtained an average value of 1.1 ppb for the total aliphatic aldehydes in surface air in the tropics. Levy (152) proposed the formation of formaldehyde via the tropospheric oxidation of methane and calculated (155) an upper limit of 1 ppb for the mixing ratio, with an altitude profile for a summer midlatitude decreasing from 0.6 ppb at the ground to less than 0.01 ppb in the upper troposphere, where methane oxidation is very slow (154). 

Carbon monoxide (CO) strongly influences the concentration of the radical OH in the tropical atmosphere. CO oxidation can lead to either production or destruction of ozone, depending on the NOx mixing ratio. Tropical soils are either a sink or a weak source of CO, where photochemical oxidation of methane and other hydrocarbons and biomass burning emissions are the predominant CO sources. 

It is interesting to note that the sources of both methane and carbon monoxide are mostly continental rather than oceanic. Because most of the world s land mass is in the northern hemisphere, the largest sources of both compounds are there. One might expect, therefore, to find an inter-hemispheric asymmetry for both methane and carbon monoxide. However, as can be seen in Figure 6, whereas considerably more carbon monoxide is found in the northern hemisphere, methane has a nearly constant mixing ratio of 1.65 ppmv with only a slight change in abundance across the ITCZ near the equator. 

By comparison, the average CO mixing ratio in Earth s troposphere is —0.12 ppmv and it is produced from a variety of anthropogenic and biogenic sources such as fossil fuel combustion, biomass burning, and oxidation of methane and other hydrocarbons. Most of the CO in Earth s troposphere is destroyed by reaction with OH radicals, which are also important for the catalytic... 

Performances of each catalyst is shown in Figure 1. The ethanol synthesis catalyst (Fe-based catalyst. Cat. 1) have both functions of F-T synthesis and alcohol synthesis. The main products were hydrocarbons, ethanol and methanol. With the increase of CO in reaction gas, the yield of ethanol increased[l]. The Cu-based catalyst (Cat. 2) converted CO2 to CO with selectivity more than 70% at a temperature range from 270 to 370°C, and other products were methanol and a slight amount of methane. Ethanol and C2 hydrocarbons were not produced. In order to harmonize the three functions, C-C bond growth, partial reduction of CO2 to CO, and OH insertion to products, the mixed ratio of Fe-based catalyst to Cu-based catalyst was coordinated at the range from Cu/Fe =... 

Carbon monoxide (CO), a toxic gas, is produced during combustion, both in wildfires and in fuel-burning devices CO also can be produced and consumed by bacterial activity. The presence of CO may indirectly increase the atmospheric mixing ratios of other gases by competing for oxidant species (such as the hydroxyl radical, OH-), thereby decreasing the oxidation rates of the other gases. This competition for oxidant species is believed to be one reason for the current increase in atmospheric methane, whose major atmospheric sink is reaction with the hydroxyl radical. 

Figure 9. The average surface concentration of methane for each of the three hydrographic domains (see Table III). The equilibrium concentration of methane ranged from about 62-68 nL/L, assuming an atmospheric mixing ratio of 1.66 ppm(v).

One may conclude that approximately 600 Tg of methane are produced each year. Since the total atmospheric burden of methane is about 4900 Tg (corresponding to a mean tropospheric mixing ratio of about 1.75 ppmv), a global atmospheric lifetime of 8 years can be derived. 

Carbon dioxide is another end product of the long chemical methane oxidation chain. The mixing ratio of CO2 is almost constant with altitude in the homosphere (typically 370 ppmv in year 2000), but... 

In the middle and upper stratosphere, where increasing water vapor mixing ratios are observed, the formation of water vapor results from methane oxidation via the mechanisms discussed in Section 5.3. In the mesosphere, the presence of water vapor leads to the formation of hydrated cluster ions, such as H+(H20)n, which have been commonly observed in the D-region (see Chapter 7). H2O photolyzes in the thermosphere and upper mesosphere by absorption of shortwave... 

Atmospheric chemistry is dominated by trace species, ranging in mixing ratios (mole fractions) from a few parts per million, for methane in the troposphere and ozone in the stratosphere, to hundredths of parts per trillion, or less, for highly reactive species such as the hydroxyl radical. It is also surprising that atmospheric condensed-phase material plays very important roles in atmospheric chemistry, since there is relatively so little of it. Atmospheric condensed-phase volume to gas-phase volume ratios range from about 3 x KT7 for tropospheric clouds to 3 x ICE14 for background stratospheric sulfate aerosol. 

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