Ozone in smog

Air pollutants are divided into two broad categories primary and secondary. Primary pollutants are those emitted directly into the air, in contrast to secondary pollutants, which are created in the atmosphere by the reactions among the primary pollutants, usually in the presence of sunlight. Specifically, a variety of chemical or photochemical reactions (catalyzed by light) produce a wide range of secondary pollutants, especially in urban air. A prime example is the formation of ozone in smog. 

Pryror, W.A. Can vitamin E protect humans against the pathological effects of ozone in smog. Am J Clin Nutr53 (1991) 702-22. 

Regener and his coworkers, in collaboration with Littman, obtained evidence of ozone in smog by its absorption in the ultraviolet (2600 to 3200 A.) using photographic spectrometry (27). Renzetti, using photoelectric spectrometry in the ultraviolet based on the same principle as Regener s instrument (26), reported values for ozone up to 35 p.p.h.m. (29). 

The important wave length range of radiation was 3000 to 4000 A. for the photochemical production of ozone in smog. 

With the increasing use of ozone in industry, the presence of an ozone layer above 50,000 feet, and the occurrence of ozone in smog conditions as in the Los Angeles area, the chronic toxicity of this gas has become an important problem. 

The kinetics of ozone formation at ground level differs substantially from that in the stratosphere. The formation of ozone in smog requires several steps. The key compound, NO2, forms in the high temperature environment of automobile engines. When NO2 absorbs sunlight, it can dissociate ... 

Why does the formation of ozone in smog depend on having less NO(g) present ... 

In addition to increased mortality, human exposure to ozone in smog decreases pulmonary functions and initiates inflammatory processes in the lung. The biochemical basis of these effects is not very well established. One possible mechanism is attack by ozone on endogenous lipids that act as surfactants in the lung. 

Materials The damage that air pollutants can do to some materials is well known ozone in photochemical smog cracks rubber, weakens fabrics, and fades dyes hydrogen sulfide tarnishes silver smoke dirties laundry acid aerosols ruin nylon hose. Among the most important effects are discoloration, corrosion, the soiling of goods, and impairment of visibility. 

Existence of the PSS was predicted theoretically by Leighton (61), and experimental studies of this relationship date back almost 20 years. These experiments have been accomplished in smog chambers (62), polluted urban air (63,64,65), rural environments (66), and in the free troposphere (67). The goal of these experiments has been to verify that our understanding of NOjj chemistry is fundamentally correct, and to ver the role of H02 and R02 in ozone formation. Studies in polluted air seem to confirm the dominance... 

These reactions are important in a cycle that oxidizes CO and hydrocarbons and produces ozone, in the presence of NO (NO + N02). In photochemical smog, ozone can build up to... 

The main environmental issue concerned with VOCs is their ability to form low-level ozone and smog through free radical air oxidation processes. The EPA has published a list detailing a number of adverse health effects, which are now thought to originate from the presence of VOCs in the environment, including ... 

The city of Los Angeles issues a smog alert when the ozone in its atmosphere reaches 0.5 ppm. This means that in every mole of air, there is 0.5 X 10 mol of ozone. This may not seem like much, but ozone is a very toxic substance that is particularly damaging to soft tissue such as the lungs. 

A reaction of ozone provides an example of concentration effects. Ozone in the atmosphere near the Earth s surface is a serious pollutant that damages soft tissues such as the lungs. In major urban areas, smog alerts are issued whenever there are elevated concentrations of ozone in the lower atmosphere. Nitmgen oxide, another component of photochemical smog, is a colorless gas produced in a side reaction in automobile engines. One reaction that links these species is the reaction of NO and O3 to produce O2 and NO2 ... 

It is important and beneficial for the environment to reduce the sulfur levels in refinery products, as well as in energy fuel (e.g. natural gas, LPG and heating oil) [1]. It has been previously reported that atmospheric emission of sulfur combustion products contributes to acid rain, ozone, and smog generation. 

Methods of measuring the components of photochemical smog are reviewed in Chapter 6. There have been significant advances in the calibration of instruments for monitoring ozone in ambient air. A method based on the absorption of ultraviolet radiation at 254 nm has been adopted by California for the calibration of air monitoring instruments. The method is based on the use of a commercially available instrument that measures ultraviolet absorption as a transfer standard in the calibration process. 

The photochemical oxidants that are observed in the atmosphere are ozone, Oj, nitrogen dioxide, NOj and peroxyacetylnitrate (PAN). Several other substances, such as hydrogen peroxide, HjO, may be classified as photochemical oxidants, but their common presence in smog is not well established. The oxidants are secondary pollutants i.e., they are formed as a result of chemical reactions in the atmosphere. Primary pollutants are those emitted directly by pollution sources. 

The major oxidant in smog is ozone, and early research efforts concentrated on the mechanism of its formation. Attention was focused on the nitrogen oxides, specifically nitrogen dioxide, because it was known... 

It is well established that both ozone and PAN can cause damage to. biologic ems (see Chapters 8 and 11). The possibility that the reactive intermediates in smog could directly cause biologic damage has been suggested, but experiments are seldom designed to test this possibility. 

In interpreting the results of human experimental studies with pure ozone in relation to the oxidant standard, it must be remembered that the other oxidants ordinarily present in smog were absent. Conceivably, a larger difference may be necessary between the lowest concentration of pure ozone at which an observed effect occurred and the air quality standard than between the lowest concentration of oxidant mixtures and the standard. 

The development of models requires more knowledge about the chemical, physical, morphologic, and flow properties of the mucus layer the kinetics of the reactions of ozone in the mucus and tissue layers and the molecular diffusivity of ozone in these layers. Similar information is needed for the hydroperozy and singlet oxygen, O, (a A), free radicals, which are reactive interme ates in photochemical smog. 

In moderately high concentrations ozone is very toxic when inhaled, and in lesser concentrations, it is irritating to the nose and eyes. Ozone in the lower atmosphere contributes to air pollution and smog. It can cause damage to rubber, plastics, and paints. These low concentrations can cause headaches, burning eyes, and respiratory irritation. It is particular harmful to asthmatics and the elderly with respiratory problems. 

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