Ozone photochemical formation

Stohl A, E Williams, G Wotawa, H Kromp-Kolb (1996) A European inventory of soil nitric oxide emissions and the effect of these emissions on the photochemical formation of ozone. Atmos Environ 30 3741-3755. 

Fig. 3.9. Photochemical formation and non-catalytic destruction of ozone. UV-C radiation (200-280 nm wavelength) UV-B radiation (280-320 nm wavelength). Note how high-quality energy (UV radiation) is converted into lower quality energy (heat). Catalysts such as freons or nitrogen oxides can destroy ozone (e.g. Cl + 03 —> CIO + 02).

Low concentrations of VOCs in ambient ah of 1 to 1,000 ppmv (parts per million based on volume) are often harmful to human health. VOCs also promote the photochemical formation of ozone and other contaminants, and in high concentrations are a fire hazard. These severe environmental implications have resulted in increasingly stringent legislation in the U.S.A. and elsewhere to limit release of VOCs into the atmosphere. Control technologies for VOCs release include combustion and vapor recovery. Vapor recovery is preferred as combustion may result in the production of other air pollutants, and destroy valuable VOCs. 

The Stratospheric Ozone Layer Its Photochemical Formation and Degradation... 

Behnke, W., and C. Zetzsch, Heterogeneous Photochemical Formation of Cl Atoms from NaCl Aerosol, NOx and Ozone, J. Aerosol Sci., 21, S229-S232 (1990). 

The mechanism for the photochemical formation of ozone in the Schu-mann-Runge continuum appears to be quite simple. It has been studied... 

Keywords Hemispheric background, Long-term trends, NOx and VOCs, Ozone, Photochemical ozone formation, Regional pollution controls... 

Formaldehyde and other aldehydes are receiving increasing attention both as toxic substances and as promoters in the photochemical formation of ozone in the atmosphere. They are released into residential buildings from plywood and particle board, insulation, combustion appliances, tobacco smoke, and various consumer products. Aldehydes are released into the atmosphere in the exhaust of motor vehicles and other equipment in which hydrocarbon fuels are incompletely burned. A sensitive method for analyzing aldehydes and ketones is based on the sorption of these compounds to an SPE sorbent and their subsequent reaction with 2,4-dinitrophenylhydrazine (DNPH) on the sorbent. They are then analyzed as their hydrazones by HPLC (Fig. 7.9). A gradient analysis by HPLC may separate as many as 17 components with detection by ultraviolet (UV) light. 

Because of the expanded scale and need to describe additional physical and chemical processes, the development of acid deposition and regional oxidant models has lagged behind that of urban-scale photochemical models. An additional step up in scale and complexity, the development of analytical models of pollutant dynamics in the stratosphere is also behind that of ground-level oxidant models, in part because of the central role of heterogeneous chemistry in the stratospheric ozone depletion problem. In general, atmospheric Hquid-phase chemistry and especially heterogeneous chemistry are less well understood than gas-phase reactions such as those that dorninate the formation of ozone in urban areas. Development of three-dimensional models that treat both the dynamics and chemistry of the stratosphere in detail is an ongoing research problem. 

Reaction (12-9) shows the photochemical dissodation of NO2. Reaction (12-10) shows the formation of ozone from the combination of O and molecular O2 where M is any third-body molecule (principally N2 and O2 in the atmosphere). Reaction (12-11) shows the oxidation of NO by O3 to form NO2 and molecular oxygen. These three reactions represent a cyclic pathway (Fig. 12-4) driven by photons represented by hv. Throughout the daytime period, the flux of solar radiation changes with the movement of the sun. However, over short time periods (—10 min) the flux may be considered constant, in which case the rate of reaction (12-9) may be expressed as... 

One strategy in limiting the formation of ozone and other photochemical oxidants has been the use (in the past) of low reactivity fuels in internal combustion engines. More recently, alternate fuels (methanol, for instance) have been proposed for regions that suffer from elevated levels of photochemical air pollution. The effect of switching to such a low-reactivity fuel may be seen in Equation E2 for methanol, which has a simple atmospheric reaction mechanism. 

Moshiri, E. Computer Modeling of Photochemical Ozone Formation A Simplified Approach Ph.D. Thesis Portland State University Portland, OR, 1984 1-211. 

VOCs - A VOC is any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metal carbides or carbonates and ammonium carbonate, which participate in atmospheric photochemical reactions1. VOCs are precursors to ground-level ozone production and various photochemical pollutants and are major components in the formation of smog through photochemical reactions2,3. There are many sources of VOCs, as will be discussed later. 

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