Ozone production/destruction

Stratospheric ozone production is balanced by various catalytic destruction sequences ... 

In this section, we use another chain reaction to show the relation between the steady-state treatment and the quasi-equilibrium treatment. The former is more general than the latter, and leads to more complete but also more complicated results. Ozone, O3, is present in the stratosphere as the ozone layer, and in the troposphere as a pollutant. Ozone production and destruction in the atmosphere is primarily controlled by photochemical reactions, which are discussed in a later section. Ozone may also be thermally decomposed into oxygen, O, although... 

Based on this chemistry, the production rate of 03 is expected to be very sensitive to the NO concentration, increasing with NO (see also Chapter 16 for a discussion of the dependence of 03 generation on NOx). In this context, Folkins et al. (1998) suggest that acetone is likely the major contributor to enhanced ozone production in the upper troposphere, since increased CH3OOH and H202 concentrations at 9- to 12-km altitude were observed only at very small NO concentrations, indicative of clean marine boundary layer air under such low NOx conditions, destruction rather than production of 03 is expected. 

The fact that dissolved ozone is produced brings a very important advantage to subsequent ozone applications mass transfer from the gas to liquid phase is not required. Efficient mixing (e. g. with static mixers) of the ozone-rich pure water stream with the (waste-)water stream to be treated, though, is required. During this in-situ ozone production, the liquid ozone concentration (cL) can easily reach the solubility level (cr ), depending on the pressure (P) and temperature (T) in the cell. Oversaturation of the feed-water will immediately occur, when the pressure drops. Due to this potential degassing, vent ozone gas destruction is also required for this system. 

Throughout the global stratosphere, many of the photochemical mechanisms remain untested. Although certain reactions are clearly occurring, they may not be the only reactions. A simple example is a test for the balance between the production and the destruction of ozone, as represented by equation 8. No experiment has yet been performed during which the abundances of all the rate-limiting components for ozone loss and ozone production, N02, H02, CIO, BrO, and O, have been measured. 

Stimulated by Levy s paper my attention turned towards tropospheric chemistry. First presented at the 1972 International Ozone Symposium in Davos, Switzerland, I proposed that in situ chemical processes could produce or destroy ozone in quantities larger than the estimated downward flux of ozone from the stratosphere to the troposphere (15, 16). Destruction of ozone occurs via reactions R5, R6 and R7 + R8. Ozone production takes place in environments containing sufficient NOx, via... 

The results clearly show the dominance of in situ tropospheric ozone production and destruction over downward transpeat from the stratosphere. With the same model, estimates were also made of the present and pre-industrial ozone concentration distributions. The calculations indicate a clear increase in tropospheric ozone concentrations over the past centuries mainly due to higher amounts of fuel (CO and CH4) and enhancements in the NO catalysts from fossil fuel and biomass burning (19-25). 

We simulated a period of three years (not nudged) to investigate the climatology of the tropospheric ozone budget and the contribution by STE. We focus on the NH where the ozone-PV relation derived from MOZAIC is applied. Figure 4 displays the seasonality of cross-tropopause transports, photochemical production/destruction, dry deposition and the tropospheric content of ozone. 

The importance of photochemical destruction in the 03s tropospheric budget implies that the lifetime of 03s is coupled to the chemical production and destruction of 03. Consequently, the simulated tropospheric budget of 03s may be affected directly by differences in the simulated chemistry. For example, simulations with a pre-industrial and a present-day emission scenario or with and without representation of NMHC chemistry will produce different estimates of the tropospheric oxidation efficiencies [39, 40]. However, our simulations indicate only small effects on the calculated 03s budget [6]. Figure 5 presents the simulated zonal distribution of 03s, the chemical destruction rate, of ozone (day"1) and the chemical loss of 03s (ppbv day 1) for the climatological April. The bulk of the 03s in the troposphere resides immediately below the tropopause, whereas the ozone chemical destruction rate maximizes in the tropical lower troposphere (Figures 5a and 5b). Hence, most 03s is photochemically destroyed between 15-25 °N and below 500 hPa. This region... 

Similar chain reactions can be written for reactions involving R02- In contrast, when relatively little NO is present, as in the remote atmosphere, the following cycle can dominate over ozone production leading to the catalytic destruction of ozone, viz ... 

This ozone production is balanced by various ozone destruction reactions. Principal among these is the catalytic reaction of O3 with NO ... 

If one accepts the classical viewpoint and assumes photochemical ozone production and loss reactions negligible on a global scale, the budget of ozone in the troposphere will be dominated by the injection of ozone from the stratosphere and its destruction at the ground surface. Clearly, this is a minimum budget. Injection and destruction rates are examined below. For steady-state conditions both rates must balance, and if they do not, one would have an indication for the importance of additional sources or sinks of tropospheric ozone. The following discussion will show, however, that within a rather wide margin of error, the two rates are indeed compatible. 

Terrestrial stratospheric chemistry is closely linked to the ozone (O3) layer at 15-35 km, which shields the Earth s surface from harmful UV sunlight (X<300 nm) and dissipates the absorbed solar energy as heat. The abundance of O3 in the stratosphere is a balance between production, destruction, and lateral transport. Production and destruction of O3 in the absence of other perturbing influences is described by the Chapman cycle given in Table V. 

Ozone (O3) exists in the atmosphere, 20-40 km above sea level. Ozone absorbs UV radiation which would otherwise harm living things. The effects of ozone loss could include increased human cataracts and skin cancer, reduction of plankton in ocean waters and destruction of plants, including crops. Ozone layer destruction in the Antarctic was reported in 1985 a major cause of this was believed to be the release of chlorofluorocarbon compounds, such as CCI2F2 (CFCs). These compounds are chemically unreactive, non-toxic and odourless, properties which at one time caused them to be used as solvents, aerosol propellants, refrigerant fluids and blowing agents for expanded plastic foams. They are so stable, however, that they persist in the atmosphere for years and eventually enter its upper layers, where they are broken down by the powerful UV radiation emitted by the sun. Their decomposition products can then destroy ozone ... 

Ozone generation from air, with air preparation equipment, ozone generator, dissolution equipment, off-gas recycling or destruction equipment, safety and monitoring equipment. FOB cost = 545 000 at ozone production rate of 0.46 g/s with n = 0.67 for the range 0.09-30. Factors air feed, X 1.00 oxygen feed, X 0.5. L-rM = 1.2-1.35. 

Reactions (1) to (3) form an equilibrium which is called the phototstationaiy state. It depends on the intensity of solar radiation. The photostationary state does not lead to a net ozone production. The ozone destruction by NO is important close to large emission sources such as busy streets, in particular in the nights (see Section III). Ox has been introduced to account for the influence of the reaction of NO with O3, because Ox is conserved by the titration of O3 by NO (reaction (3)) ... 

The reactions of photochemical production of ozone and destruction of ozone lead to a photochemical equilibrium, which maintains a small concentration of ozone in the oxygen being irradiated. The layer of the atmosphere in which the major part of the ozone is present is about 15 miles above the earth s surface it is called the ozone layer. 

Ozone in the stratosphere is present at a steady-state concentration resulting from the balance of ozone production and destruction by the above processes. The quantities of ozone involved are interesting. A total of about 350,000 metric tons of ozone are formed and destroyed daily. Ozone never makes up more than a minuscule fraction of the gases in the ozone layer. In fact, if all the atmosphere s ozone were in a single layer at surface temperature and pressure conditions of approximately 273 K and 1 atm, it would be only 3 mm thick ... 

Fig. 1.1 Ozone Production and destruction rates, including absolute and relative contributions by the Chapman reaction R4 (Do), NO catalysis Rll + R12 (Dn), HO catalysis R5 + R6 (Dh) and ClOx catalysis R21 + R22 (DCl)x. The calculations neglect the heterogeneous halogen activation which become very important below 25 km under cold conditions...

This reaction chain requires the presence of sufficient NO. At low NO volume mixing ratios, below about 10 pmol moF oxidation of CO may lead to ozone destruction, since the HO2 radical then reacts mostly with O3 [see Eq (6)]. The result of the participating reactions [(18) + (19) + (6)] is CO + O3 —> CO2 + O2. In a similar way, the oxidation of CH4 in the presence of sufficient NOx will lead to tropospheric ozone production. 

A8. Crutzen, P.J., 1975 Physical and Chemical Processes Which Control the Production, Destruction and Distribution of Ozone and Some Other Chemically Active Minor Constituents , in GARP Publications Series 16, World Meterological Organization, Geneva, Switzerland. 

In the years 1972-1974 Cmtzen proposed that NO and NO2 could catalyse ozone production in the background troposphere by reactions occurring in the CO and CH4 oxidation chains. Additional photochemical reactions leading to ozone loss were likewise identified. These gross ozone production and destruction terms are each substantially larger than the downward flux of ozone from the stratosphere, which until then had been considered the main source of tropospheric ozone. 

Figure 3.4. Long-range transport of aerosols and gases and effects on ozone production and destruction [4],...

Despite their instability (or perhaps because of it) the oxides of chlorine have been much studied and some (such as CI2O and particularly CIO2) find extensive industrial use. They have also assumed considerable importance in studies of the upper atmosphere because of the vulnerability of ozone in the stratosphere to destruction by the photolysis products of chlorofluorocarbons (p. 848). The compounds to be discussed are ... 

Oxidation-reduction reactions in water are dominated by the biological processes of photosynthesis and organic matter oxidation. A very different set of oxidation reactions occurs within the gas phase of the atmosphere, often a consequence of photochemical production and destruction of ozone (O3). While such reactions are of great importance to chemistry of the atmosphere - e.g., they limit the lifetime in the atmosphere of species like CO and CH4 - the global amount of these reactions is trivial compared to the global O2 production and consumption by photosynthesis and respiration. 

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