Production and Destruction of Ozone

From the preceding discussion of atmospheric photochemistry and NO chemistry, it can be seen that the fate of the peroxy radicals can have a marked effect on the ability of the atmosphere either to produce or to destroy ozone. Photolysis of NO2 and the subsequent reaction of the photoproducts with O2 (reactions (2.4) and (2.20)) are the only known way of producing ozone in the troposphere. In the presence of NO the following cycle for the production of ozone can take place  

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  

It is also worth noting that PiO ) can also be expressed in terms of the concentrations of NO , 72.2(N02), O3 and temperature by substitution of Equation (2.27) into Equation (2.33) to give 

At some concentration of NO the system reaches a maximum production rate for ozone at dP(03)/d(N0 c) = 0 and even though P(03) is still significantly larger than 2.(03) the net production rate begins to fall off with increasing NO - Until this maximum is reached the system is said to be NO c limited with respect to the production of ozone. The turn-over, i.e. dP(03)/d(NO t) = 0 is caused by the increased competition for NO by the reaction 

In reality, the situation is somewhat more complicated owing to the presence at high concentrations of NO , of increased levels of nonmethane hydrocarbons (NMHCs), especially in places such as the urban 

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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. 

For centuries, the production and destruction of ozone in Earth s ozone layer was constant. Explain why in recent decades the ozone has been depleted faster than it was replaced. 

Figure 1.3 Chemical reactions involved in the production and destruction of ozone ...

The first issue is the possibility raised in the early 1970 s that human activities might add certain chlorine, nitrogen, and other catalytic substances to the stratosphere. These substances, in turn, would upset the balance between the production and destruction of ozone in a manner that could increase the intensity of ultraviolet light reaching the biosphere with... 

Located several kilometres above the Earth s surface is the stratosphere. Here the ozone layer acts as a filter, protecting life on Earth from harmful low-wavelength ultraviolet radiation known as UV-C, which damages biological macromolecules such as proteins and DNA. In order to understand the effects of anthropogenic input into the stratosphere, the production and destruction of the ozone layer has been studied by a variety of photochemical models and experimental methods. 

With the addition of Reactions 2-173 and 2-174, the production and consumption of ozone include both chain and parallel reactions. The method of solution is nonetheless similar to the case without anthropogenic ozone destruction. To solve for the concentration of [O3], it is necessary to solve for [XO], [O], and [O3] from three equations d[XO]/df=0, d[O]/df=0, and d[O3]/df=0. 

Silent Electric Discharge. Commerdal production and utilization of ozone by silent electric discharge consists of live basic unit operations gas preparation, electrical power supply, ozone generation, contacting (i.e., ozone dissolution in water), and destruction of ozone in contactor off-gases. 

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... 

Carbon monoxide (CO) strongly influences the concentration of the radical OH in the tropical atmosphere. CO oxidation can lead to either production or destruction of ozone, depending on the NOx mixing ratio. Tropical soils are either a sink or a weak source of CO, where photochemical oxidation of methane and other hydrocarbons and biomass burning emissions are the predominant CO sources. 

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. 

In air, the O atoms produced photochemically combine with O2 in the presence of a third body to yield O3 by the reaction already discussed (Section 1.A.4). Ozone itself, however, is readily photodissociated, and also reacts with NO to reform O2 and NO2. The rates of production and destruction of O3 in an air-nitrogen oxide system are such that the concentrations of NO and O3 should be roughly equal. In practice, however, the combination of NO and hydrocarbons plus solar ultraviolet leads to a net production of O3 and other oxidants. 

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. 

The term CFCs is a general abbreviation for ChloroFluoroCarbons. They have been extensively used since their discovery in the thirties, mainly as refrigerant, foam blowing agent, or solvent because of their unique properties (non toxic, non flammable, cheap). However, after the first warning of Rowland and Molina [1] in 1974 that CFCs could destroy the protective ozone layer, the world has moved rapidly towards a phase-out of CFCs. Because the destruction of stratospheric ozone would lead to an increase of harmful UV-B radiation reaching the earth s surface, the production and use of CFCs is prohibited (since January 1, 1995 in the European Union and since January 1, 1996 worldwide). 

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). 

On the global-scale, the destruction of ozone by halocarbons was addressed in the U.S. by banning chlorofluorocarbons in aerosol products. The release of carbon dioxide to the atmosphere from fossil fuel combustion wil1 continue well into or through the twenty-first century. Energy requirements of nations of the temperate zone will require combustion of gas, oil and coal and the atmospheric burden of carbon dioxide will continue to increase with uncertain consequences. 

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