Residence trace gases

Carbon monoxide is an important trace gas, which has a mean residence time of about two months and a mean concentration of the order of 0.1 ppm. The principal sources of CO are (1) oxidation of methane and other higher hydrocarbons, (2) biomass burning, (3) traffic, industry and domestic heating, (4) oceans, and (5)... 

The average residence time of an air parcel in the upper stratosphere (above approximately 16 km) is approximately 2 years. The stratosphere should not be regarded as fully mixed, however. Upwelled layers of air, their exact chemical composition changing with season, have been shown to retain an identity for many months. Another example of stratospheric heterogeneity is the air in polar stratospheric vortices (see Section 4.6.4, Fig. 4-41 later) these vortices may have a trace gas chemistry that differs from that of stratospheric air in the tropics. 

Trace gas Mixing ratio Distribution Major sources (Tg y ) Major sinks (Tgy ) Residence time... 

A route of chemical recycling by pyrolysis has been examined (71). The pyrolysis of COC was performed in a fluidized-bed reactor. Various parameters, such as pyrolysis temperature, fluidizing gas or residence time were varied. Under favorite conditions, the undesired tar fraction could be reduced to a minimum of around 10%. Up to 44% of valuable gases and 45% of aromatic light oils could be obtained at a pyrolysis temperature of 700°C. In general, nor-bornene was recovered only in traces. Thus, it is concluded that 2-norbomene is not sufficiently stable to resist the conditions of pyrolysis. Actually, a retro-Alder reaction occurs resulting in ethene and cyclopentadiene. 

The zinc salt and BaS solutions are mixed thoroughly under controlled conditions (vessel geometry, temperature, pH, salt concentration, and stirring speed, see (a) in Fig. 20). The precipitated raw lithopone does not possess pigment properties. It is filtered off (b2) and dried (c) ca. 2 cm lumps of the material are calcined in a rotary kiln (d) directly heated with natural gas at 650-700 °C. Crystal growth is controlled by adding 1-2 wt% NaCl, 2 wt % Na2S04 and traces of Mg2 + (ca. 2000 ppm), and K+ (ca. 100-200 ppm). The temperature profile and residence time in the kiln are controlled to obtain ZnS with an optimum particle size of ca. 300 nm. 

Pcrfluoropropanoic acid (16.4 g. 0.1 mol) was passed through a quartz tube heated to 650 C using as the carrier gas. The residence time in the tube was about 3 s. The products contained 85 -90% tetra-fluoroethene, 10% pentafluoroethane, and traces ofhexafluoropropene and perfluorocyclobutane. 

CO2, and has an average residence time in the atmosphere of 5-10 years. Carbon monoxide has an atmospheric residence time of only a few months. Its low concentration, —0.1 ppm, and its short residence time result from its chemical reactivity with OH radicals. Carbon monoxide is not a greenhouse gas, but its chemical reactivity affects the abundances of ozone and methane which are greenhouse gases. Non-methane hydrocarbons, another unstable form of carbon in the atmosphere, are present in even smaller concentrations. The oxidation of these biogenic trace gases is believed to be a major source of atmospheric CO, and, hence, these non-methane hydrocarbons also affect indirectly the Earth s radiative balance. 

For glucose, complete conversion and constant gas phase composition is already obtained at 30 s (FigureS). At feed concentrations higher than 0.6 M and the low potassium concentrations used, a considerable decrease of the gasification efficiency as well as small formation of soot and tar is observed at a residence time of 120 sec. A marked pressure effect is observed for the CH4 yield. The CH4 content in the product gas increases from about 3 vol% at 250 bar to about 8 vol% at 450 bar along with a decrease of H2 of about 60 vol% at 450 bar to about 50 vol% at 250 bar. For these experiments, the closure of the carbon balance is better than 96% and no or only traces... 

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