Carbon dioxide atmospheric level

Regarding the first question, at the beginning of the Industrial Revolution carbon dioxide was present in the atmosphere at concentrations of about 270 parts per million by volume (ppmv). By 2000, carbon dioxide levels had risen to more than 370 ppmv. This is a change of more than 33 percent above preindustrial levels. All reputable studies have shown that, even with aggressive mitigation policies, carbon dioxide atmospheric content will have increased to 200 percent of its preindustrial levels by the turn of the next century. 

Replacement of chemical fumigants with nitrogen and/or CO2 atmospheres has been reviewed (Bailey and Banks, 1980). Recent work has emphasised that oxygen is the key factor and that levels of 1% or less, coupled with low temperatures are required (Fleurat-Lessard, 1990). These atmospheres offer opportunities for preservation of cereal products and dried fruits and vegetables, possibly in conjunction with active packaging . Hence provision of a barrier to diffusive loss of nitrogen or carbon dioxide atmospheres could help to avoid the presence of chemical residues as unintended additives. 

Anhydrous, monomeric formaldehyde is not available commercially. The pure, dry gas is relatively stable at 80—100°C but slowly polymerizes at lower temperatures. Traces of polar impurities such as acids, alkahes, and water greatly accelerate the polymerization. When Hquid formaldehyde is warmed to room temperature in a sealed ampul, it polymerizes rapidly with evolution of heat (63 kj /mol or 15.05 kcal/mol). Uncatalyzed decomposition is very slow below 300°C extrapolation of kinetic data (32) to 400°C indicates that the rate of decomposition is ca 0.44%/min at 101 kPa (1 atm). The main products ate CO and H2. Metals such as platinum (33), copper (34), and chromia and alumina (35) also catalyze the formation of methanol, methyl formate, formic acid, carbon dioxide, and methane. Trace levels of formaldehyde found in urban atmospheres are readily photo-oxidized to carbon dioxide the half-life ranges from 35—50 minutes (36). 

Conventional nitrocellulose lacquer finishing leads to the emission of large quantities of solvents into the atmosphere. An ingeneous approach to reducing VOC emissions is the use of supercritical carbon dioxide as a component of the solvent mixture (172). The critical temperature and pressure of CO2 are 31.3°C and 7.4 MPa (72.9 atm), respectively. Below that temperature and above that pressure, CO2 is a supercritical fluid. It has been found that under these conditions, the solvency properties of CO2 ate similar to aromatic hydrocarbons (see Supercritical fluids). The coating is shipped in a concentrated form, then metered with supercritical CO2 into a proportioning airless spray gun system in such a ratio as to reduce the viscosity to the level needed for proper atomization. VOC emission reductions of 50% or more are projected. 

The current debate over controversial global warming theories will continue. The impact of carbon dioxide levels in the atmosphere, whether they are increasing or not over time, and the effect on climate and economics will continue to he discussed. A solution, if it is needed, may evolve—or not. 

Carbon dioxide, considered a wanning gas, comprises about 0.036 percent of the atmosphere by volume. As Figure 1 shows, carbon dioxide levels have increased as a component of the atmosphere by nearly 30 percent from the late eighteenth century to the end of the twentieth century, when the level was close to 365 parts per million by volume. Prior to the period of industrialization, carbon dioxide levels were largely stable, at about 280 parts per million, though fluctuations as low as 200 parts per million or as high as 300 parts per million have been observed through analysis of air bubbles trapped in arctic ice cores. 

Table 1 lA presents tabulations of the safety of important refrigerants, but this list does not include aU available refrigerants. Table 11-5 summarizes a limited list of comparative hazards to life of refrigerant gas and vapor. The current more applicable refrigerants from the m or manufacturers of the CFC and HCFC refrigerants and their azeotropes/ blends/mrxtures are included, but the list excludes the pure hydrocarbons such as propane, chlorinated hydrocarbons such as methyl chloride and others, inorganics, ammonia, carbon dioxide, etc. See Table 11-6. The CFC compounds have a longer and more serious ozone depletion potential than the HCFC compounds, because these decompose at a much lower atmospheric level and have relatively short atmospheric lifetimes therefore, they do less damage to the ozone layer. Table 11-7 summarizes alternate refrigerants of the same classes as discussed previously. Table 11-8 correlates DuPont s SUVA refrigerant numbers to the corresponding ASHRAE numbers.

It should be noted that in intermittently operated steam processes, where condensate is allowed to cool in carbon dioxide-rich atmospheres, the pH level can drop significantly, resulting in devastatingly high localized corrosion, even though the average C02 content of the steam may be relatively low. 

Berner, R, A. (1990). Atmospheric carbon dioxide levels over Phanerozoic time. Science, 249, 1382-1386. 

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