Methane, tropospheric

Recent estimates indicate that the level of carbon dioxide in the atmosphere has increased by a third since the beginning of the industrial age, and that it contributes significantly to global warming. Other major contributors include methane, tropospheric ozone, and nitrous oxide. Methane is the principal component of natural gas, but it is also produced by other sources such as rice paddies and farm animals. Tropospheric ozone is generated naturally and by the sunlight-... 

Carbon dioxide, methane, tropospheric ozone, the CFCs, and nitrous oxide contribute most to the greenhouse effect. HCFCs represent less than 1%, the chlorinated solvents part is roughly estimated at 0.04 % of the total. 

HO oxidation of CO is much faster than the reaction with methane, resulting in a mean CO lifetime of about two months, but considerably slower than reaction with the majority of the nonmethane hydrocarbons. Table I gives representative removal rates for a number of atmospheric organic compounds their atmospheric lifetimes are the reciprocals of these removal rates (see Equation E4, below). The reaction sequence R31, R13, R14, R15 constitutes one of many tropospheric chain reactions that use CO or hydrocarbons as fuel in the production of tropospheric ozone. These four reactions (if not diverted through other pathways) produce the net reaction... 

When NMHC are significant in concentration, differences in their oxidation mechanisms such as how the NMHC chemistry was parameterized, details of R02-/R02 recombination (95), and heterogenous chemistry also contribute to differences in computed [HO ]. Recently, the sensitivity of [HO ] to non-methane hydrocarbon oxidation was studied in the context of the remote marine boundary-layer (156). It was concluded that differences in radical-radical recombination mechanisms (R02 /R02 ) can cause significant differences in computed [HO ] in regions of low NO and NMHC levels. The effect of cloud chemistry in the troposphere has also recently been studied (151,180). The rapid aqueous-phase breakdown of formaldehyde in the presence of clouds reduces the source of HOj due to RIO. In addition, the dissolution in clouds of a NO reservoir (N2O5) at night reduces the formation of HO and CH2O due to R6-RIO and R13. Predictions for HO and HO2 concentrations with cloud chemistry considered compared to predictions without cloud chemistry are 10-40% lower for HO and 10-45% lower for HO2. 

Etheridge, D. M., Pearman, G. I., and Fraser, P. J. (1992). Changes in tropospheric methane between 1841 and 1978 from a high accumulation rate Antarctic ice core. Tellus 44B, 282-294. 

Methane sulfonic acid is produced by tropospheric oxidation of methyl sulfides, and there are naturally occurring sulfonates including derivatives of taurine and of glucose-6-sulfonate (sulfoquinovose),... 

Important weather details are not only provided by the newest information from the Cassini orbiter the Very Large Telescope in the Atacama desert and the W. M. Keck Observatory on Hawaii are also involved. Near-IR spectra show increased cloudiness in the Titanian troposphere on the morning side, i.e., there are methane clouds at a height of about 30 km and methane drizzle at the surface (Adamkovics et al., 2007). 

The temperatures in the troposphere allow methane to reach its saturated vapour pressure and hence the potential to condense and produce precipitation. This suggests that regions of the surface may be covered with liquid methane or, more... 

Air pollution in cities can be considered to have three components sources, transport and transformations in the troposphere, and receptors. The sources are processes, devices, or activities that emits airborne substances. When the substances are released, they are transported through the atmosphere, and are transformed into different substances. Air pollutants that are emitted directly to the atmosphere are called primary pollutants. Pollutants that are formed in the atmosphere as a result of transformations are called secondary pollutants. The reactants that undergo the transformation are referred to as precursors. An example of a secondary pollutant is troposphere ozone, O3, and its precursors are nitrogen oxides (NO = NO + NO2) and non-methane hydrocarbons, NMHC. The receptors are the person, animal, plant, material, or urban ecosystems affected by the emissions (Wolff, 1999). 

Taylor JA, Brasseur GP, Zimmermann PR, Cicerone RJ. 1991. A study of the sources and sinks of methane and methyl chloroform using a global three-dimensional Lagrangian tropospheric tracer transport model. Journal of Geophysical Research 96D 3013-3044. 

Theoretical interpretation of the experimental observations will help in determining the relative roles played by stratospheric injection, plant emission, background methane, and transport to surfaces in the natural portion of the tropospheric ozone cycle. 

This is a very broad conclusion, and additional measurements must be made. Some of this effort (which is current) should address the problem of other pollutants and condensation nuclei that accompany the nonurban oxidant. Interpretation of these measurements will increase the specificity of separating anthropogenic sources from natural background sources. Theoretical assessments of the existing observations will shed light on the relative roles played by stratospheric injection, plant emission, background methane, and diy deposition on surfaces in the natural portion of the tropospheric ozone cycle. 

Photolysis of an aqueous solution containing chloroform (314 pmol) and the catalyst [Pt(cohoid)/Ru(bpy) /MV/EDTA] yielded the following products after 15 h (mol detected) chloride ions (852), methane (265), ethylene (0.05), ethane (0.52), and unreacted chloroform (10.5) (Tan and Wang, 1987). In the troposphere, photolysis of chloroform via OH radicals may yield formyl chloride, carbon monoxide, hydrogen chloride, and phosgene as the principal products (Spence et al., 1976). Phosgene is hydrolyzed readily to hydrogen chloride and carbon dioxide (Morrison and Boyd, 1971). 

Historically, organics in the troposphere have been measured as non-methane hydrocarbons (NMHC). As... 

The first thing that stands out in Table 6.2 is that the OH-CH4 rate constant, 6.2 X 10 15 cm3 molecule 1 s-1, is much smaller than those for the higher alkanes, a factor of 40 below that for ethane. This relatively slow reaction between OH and CH4 is the reason that the focus is on non-methane hydrocarbons (NMHC) in terms of ozone control in urban areas. Thus, even at a typical peak OH concentration of 5 X 106 molecules cm 3, the calculated lifetime of CH4 at 298 K is 373 days, far too long to play a significant role on urban and even regional scales. Clearly, however, this reaction is important in the global troposphere (see Chapter 14.B.2b). 

The destruction of 03 by chlorine and bromine can be short-circuited by removing either Cl and Br or, alternatively, CIO and BrO. For chlorine atoms, this occurs by reaction with methane that has been transported from the troposphere ... 

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