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Colib blue hazes that are observed over forested areas such as the Great Smoky Mountains in North Carolina and the Blue Mountains in Australia result from the reaction of natural hydrocarbons in sunlight—in the absence of much NOX and hence largely without its involvement—to produce carboxylic acids that bzird to form suspended particles of the size that scatter sunlight and thereby produce a haze. Explain your results in terms of the chemistry discussed above.
Indeed, ozone concentrations on weekends, when there is much less truck traffic, are higher in Los Angeles and many other cities, since the very high weekday levels of NO2 are lower then and so less of it is available to combine with and provide a sink for OH.
Thus, for example, when the VOC concentration is about 0. Some of the ozone molecules present above the forests react with the.
Deciduous trees and shrubs emit the gas isoprene, whereas conifers emit pinene and limonene; all three hydrocarbons contain C RC bonds. Photochemical Smog 89 The nitrogen dioxide then photochemically decomposes to produce the free oxygen atoms that react with O2 to produce ozone, as previously discussed see Figure HNO3 Consequently, lowering the NOX concentration actually produces more ozone, not less, since more OH is thereby available to react with the VOCs, although production of other smog reaction products such as nitric acid is thereby reduced.
In urban atmospheres, the concentration of these natural reactive hydro- carbons normally is much less than that of the anthropogenic hydrocarbons, and it is not quimicz the latter are reduced substantially that the influence of these natural substances becomes noticeable.
Do your results support the characterization of that zone of the graph as VOC limited? Thus, when the VOC level is 0. For example, reducing the concentration of VOCs from 1.
Química ambiental – Colin Baird – Google Books
For this reason, control of emissions of all VOCs is required in areas with serious photochemical smog problems. Points A, B, and C denote conditions discussed in the text.
National Academy Press, Regulations in California with Los Angeles especially in mind limit the use of hydrocarbon-containing products such as barbeque-grill starter fluid, household aerosol sprays, and oil-based paints that consist partially of a hydrocarbon solvent that evaporates into the air as the paint dries.
The relationships between the NOX and the VOC con- centrations that produce contours for three different values for the concen- tration of ozone are shown. Enviado por Andresa flag Denunciar.
The air quality in this region has improved because of current emission controls, but the increase in vehicle-miles driven and the hydrocarbon emissions from non-transportation sources such as solvents have thus far prevented a more complete solution.
Although hydrocarbons with Baifd RC bonds and aldehydes are the most reactive types in photochemical smog quuimica, other VOCs play a signifi- cant role after the first few hours of a smog episode have passed and the concentration of free radicals has risen.
Colin Baird, Michael Cann Química Ambiental 5° ed. English
Research has cokin indicated quimics any substantial increase in the emissions of methane to the atmosphere could prolong and intensify the periods of high ozone in the United States, even though CH4 is usually considered to be a rather unreactive VOC.
As an air mass moves from an urban colkn to a rural one downwind, it often changes from being VOC-limited to being NOX limited, since there are few sources of nitro- gen oxides, but often substantial ones of reactive VOCs, outside of cities, and since the reactions that consume nitrogen oxides occur more quickly than do those that consume VOCs. Gasoline, which is a complex mixture of hydrocarbons, is now formulated in order to reduce bairc evaporation, since gasoline vapor has been found to con- tribute significantly to atmospheric concentrations of hydrocarbons.
Point A repre- sents a typical set of conditions in colln the ozone production is NOX limited. Computer modeling indicates that NOX reduction, rather than VOC reduction, would be much more effective in reducing ozone in most of the eastern United States.
However, a reduction of the NOX level, from about 0. In the portion of the VOC-limited region that lies to the left of the diago- nal dashed line of Figurethere is a large excess of NOX; under such conditions, the OH radical tends to react with NO2, and so less of it is avail- able to initiate the reaction of more VOCs: In areas affected by the pres- ence of vegetation, then, only the reduction of emissions of nitrogen oxides will reduce photochemical smog production xmbiental.
An example of the predictions that arise from the modeling studies is shown in Figure