Residence time in atmosphere

The Bi/Pb ages of 5 to 8 d found by Fry Menon (1962) and Moore et al. (1972, 1973) are comparable with the results of Table 1.11 and also with the Tr value of 9 d observed for the disappearance of 137Cs from the atmosphere after the Chernobyl accident (Fig. 2.8). In Hawaii, with oceanic air, the Bi/Pb ratio indicates a longer residence time. 

The Po/Pb derived residence lives ranging from 19 to 50 d are longer than the Bi/Pb lives. Possible explanations are as follows  

A small proportion of air derived from a long-residence reservoir will affect the apparent Po/Pb age more than the Bi/Pb age. For example, if the mixture is 85% tropospheric with TR = 5 d and 15% stratospheric with Tr = 200 d, the apparent Bi/Pb age is 7 d and the apparent Po/Pb 

Another possibility is the volatilisation of 210Po from soil or vegetation. In the laboratory, polonium is notorious for its ability to transfer from one surface to another. Abe Abe (1969) found that 60% of 210Po collected on a filter paper volatilised on heating to 200°C for one hour. The inventory of 210Po in topsoil is about 5000 times the inventory in air, when both are expressed per unit area of ground, so only a small degree of volatilisation or resuspension would materially increase the concentration in air. 

Bismuth was irradiated in the Windscale reactor to make 210Po for use in nuclear weapons, and in the reactor fire of October 1957, an estimated 8.8 TBq (240 Ci) of 210Po was released to atmosphere (Crick Linsley, 1983). The fact that 210Po was released was published at the time (Stewart Crooks, 1958 Blok, 1958). 

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In the same way, the concentration of PAHs were measured in the industrial area in Greater Cairo, the obtained values were much higher than recorded for the industrial areas for many eoimtries such as New Jersey, Canada and Belgium. This may be due to the higher local emission of PAHs from the coke factory, iron and steel factory and other industries in and around this area. PAHs are normally associated with small particles that generally have long residence times in atmosphere and, for that reason have the potential to be transported to quite long distances (Hassan, 2006). 

Gas Principal biological source Residence time in the atmosphere... 

The deposition velocities depend on the size distribution of the particulate matter, on the frequency of occurrence and intensity of precipitation, the chemical composition of the particles, the wind speed, nature of the surface, etc. Typical values of and dj for particles below about 1 average residence time in the atmosphere for such particles is a few days. 

Stabilizers counter the effect of the high temperatures and the oxygen rich atmosphere experienced by the resin during the rotational molding process. Since some rotational molded parts require up to one hour of residence time in the oven, such stabilizers are essential. Without them, the polymer would lose its inherent properties, becoming unfit for the final application. 

In operating a fluidized bed reactor such as a fluidized bed coal gasifier, fine particles tend to be elutriated from the fluidized bed. The elutriated fines, if not recovered, represent a significant carbon loss and thus a significant loss of reactor efficiency. In actual industrial practice, the fines are recycled back to the fluidized bed for further consumption. The location of the fines reinjection point into the fluidized bed reactor is important in order to maximize the consumption of fines in each pass. Otherwise, the fines will build up in the recycle loop and increase the heat load of the reactor operation. The fines reinjection location is selected to maximize the fines residence time in the bed and to provide an conducive environment for consumption, such as high temperature and an oxidizing atmosphere. 

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. 

Their residence time in the atmosphere is relatively short (months to a few years). Changes in their production rates are therefore relatively unattenuated and reflected in precipitation with good time resolution. 

Hydrochlorofluorocarbon-141b, or 1,1-dichloro-l-fluoroethane (HCFC141b), has been developed as a replacement for fully halogenated chlorofluorocarbons because its residence time in the atmosphere is shorter, and its ozone depleting potential is lower than that of presently used chlorofluoro... 

Lyman, W. 1982. Atmospheric Residence Time. In Handbook of Chemical Property Estimation Methods, Environmental Behavior of Organic compounds. Lyman, W.J., Reehl, W. F., and Rosenblatt D.H., eds. McGraw Hill Book company, New York, NY. 10-2-10-33. 

Atmospheric transport of chlordecone particles was reported as a result of emissions from a production facility in Virginia. Chlordecone concentrations at up to 15.6 miles away ranged from 1.4 to 20.7 ng/m (Epstein 1978). The long-range transport properties of chlordecone indicate that at least a portion of the emissions were of a fine particle size having a relatively long residence time in the atmosphere (Lewis and Lee 1976). 

Primary outputs are produced essentially by sedimentation and (to a much lower extent) by emissions in the atmosphere. The steady state models proposed for seawater are essentially of two types box models and tube models. In box models, oceans are visualized as neighboring interconnected boxes. Mass transfer between these boxes depends on the mean residence time in each box. The difference between mean residence times in two neighboring boxes determines the rate of flux of matter from one to the other. The box model is particularly efficient when the time of residence is derived through the chronological properties of first-order decay reactions in radiogenic isotopes. For instance, figure 8.39 shows the box model of Broecker et al. (1961), based on The ratio, normal-... 

The most common route of exposure for the general population is probably inhalation. However, cresols have a short residence time in both day- and night- time air despite continual releases of cresols to the atmosphere, levels are probably low. Very few atmospheric monitoring data are available in the literature therefore, an average daily intake via inhalation was not calculated. Cigarette smoke is also a source of atmospheric exposure. An individual who smokes two packs of cigarettes a day may inhale 3.0 pg/day (Wynder and Hoffman 1967). 

The dry deposition velocity of lead-212, a thoron (thoron or radon-220 itself originating from thorium-232) decay product has been reported to be in the range 0.03-0.6 cm/sec (Bigu 1985 Rangarajan et al. 1986). These low deposition velocities indicate that the thoron daughter, stable lead, may have a long residence time in the atmosphere with respect to dry deposition. 

Steam-cracking reactors typically consist of several steel tubes, perhaps 100 m long and 4 in. in diameter in a tube furnace with reactants and steam fed through the several tubes in parallel. The ceramic fined furnace is heated by burning natural gas at the walls to heat the tubes to 900°C by radiation. The reactor is fed by ethane and steam in a ratio of 1 1 to 1 3 at just above atmospheric pressure. The residence time in a typical reactor is approximately 1 sec, and each tube produces approximately 100 tons/day of ethylene. We will return to olefins and steam cracking in Chapter 4. 

Once emitted, individual compounds may react chemically in three post-emission stages First, while suspended in the atmosphere before being sampled, the compound may react in the presence of solar radiation and various reactive species such as hydroxyl radicals and ozone. For example, the average residence time in the Los Angeles atmosphere of a parcel of air is of the order of ten hours. 

Weinstock, B Carbon Monoxide Residence Time in the Atmosphere, Science, 166, 224-225 (1969). 

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