Photochemical smog hydroxyl radical

If we were to increase N02 concentrations (in a way that did not use 03), then the equilibrium could be maintained by increasing 03 concentrations. This happens in the photochemical smog through the mediation of hydroxyl (OH) radicals in the oxidation of hydrocarbons. Here we will use methane (CH4) as a simple example of the process ... 

The hydroxyl radical is central in tropospheric chemistry and photochemical smog formation. The hydroxyl radical OH is continually being formed and consumed in the troposphere and it has very short half-life due to its high reactivity, especially in urban polluted air. This species carries no charge, and is therefore chemically distinct from hydroxyl ion, OH", which has an additional electron. The major route for the formation of hydroxyl radical in the troposphere occurs by a complicated mechanism. 

Explain the chemistry of hydroxyl radical in photochemical smog. What are the main sources of OH in rural and urban areas ... 

The VOCs originate from anthropogenic and biogenic sources many species are important reactants in the formation of photochemical smog. The reactive species are readily oxidized by hydroxyl radical (OH), forming a complex mixture of peroxy radicals which oxidize NO to NO2 without consuming O3 and thus allowing O3 to increase in the daytime atmospheric boundary layer (see, e.g.. Refs. 1,2). The compositions, concentrations, and reactivities of the VOCs which... 

Chemistry of the atmosphere review of gas-phase reactions radical reactions and thermodynamics chlorine radicals and the ozone layer , CFCs and other ozone depleting contaminants, catalysis on condensed phases hydroxyl radical, ozone production, proton abstraction, VOCs, NOx, and photochemical smog (four lectures)... 

Also characteristic ate the particulate secondary pollutants sulfate and nitrate, the latter being especially associated with photochemical smog processes. Nitrate formation during daytime occurs through reaction of nitrogen dioxide with the hydroxyl radical, with subsequent neutralization of nitric acid vapor by ammonia to form ammonium nitrate (NH4NO3) particles, which equilibrate with their gas-phase precursors and are termed semivolatile ... 

As discussed in greater detail in Chapter 7 with respect to atmospheric reactions of air pollutants, hydroxyl radical, HO-, is the most important reactive intermediate in atmospheric chemical reactions. Ultraviolet radiation is very much involved in the formation of hydroxyl radical through various photochemical reactions, and depletion of UV-absorbing stratospheric ozone may increase the levels of this species. The HO- radical is very active in determining the fates of atmospheric methane, carbon monoxide, hydrochlorofluorocarbons and hydrofluorocarbons that are substitutes for ozone-depleting CFCs, and other gases relevant to climate and ozone levels, and it is very much involved in the formation and dissipation of photochemical smog (see Chapter 7, Section 7.8). 

Describe the role of the hydroxyl radical in the production of photochemical smog. 

In the presence of organic matter, hydroxyl radical is produced in abundant quantities as an intermediate in the formation of photochemical smog (see Chapter 16). To a certain extent in the atmosphere, and for laboratory experimentation, HO is made by the photolysis of nitrous acid vapor ... 

Paul continued to make major contributions to stratospheric chemistry. For example, he explained how nitric acid clouds cause the Antarctic ozone hole. At the same time, he also turned his attention to the troposphere, which is the air layer that connects with the biosphere and where weather and climate take place. The troposphere is also prone to air pollution, while it is cleaned by oxidation reactions. The self-cleaning capacity relies on the presence of reactive hydroxyl radicals that convert pollutant gases into more soluble compounds that are removed by rain. The primary formation of hydroxyl radicals in turn is from ozone. While most ozone is located in the stratosphere, protecting life on Earth against harmful ultraviolet radiation from the Sun, a small amount is needed in the troposphere to support the self-cleaning capacity. While previous theories had assumed that tropospheric ozone originates in the stratosphere, Paul discovered that much of it is actually chemically formed within the troposphere. The formation mechanism is similar to the creation of ozone pollution in photochemical smog . 

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