O o2 o3

According to the results of Problem 1-3, light having wavelength less than 394 nm is capable of producing photochemical decomposition of NOz. The absorption spectrum of nitrogen dioxide gas in the UV-A region, shown in Figure 3-2, indicates that the gas does indeed absorb in this region, and sunlight having wavelengths of about 394 nm or shorter is found to efficiently induce decomposition.

As discussed above, it is predominantly NO rather than N02 that is emitted from vehicles and power plants into the air. In episodes of photochemical air pollution, NO is oxidized to the dioxide gradually over a period of several hours in complex reaction sequences that involve free radicals as catalysts (see Figure 3-3). Indeed, one can see (Figure 3-4) the concentration of NO first rising from emissions from early-morning vehicle traffic and then falling during the morning as it is converted to N02 in urban atmospheres on smog days.

The concentration of ozone does not rise significantly in a city generating smog until late in the morning (see Figure 3-4), when the NO concentration

free radicals , free radicals ,

sunlight sunlight hno3, organic nitrates, H202

FIGURE 3-3 Summary of photochemical smog reactions discussed in detail in Chapter 5.

Coping with Asthma

Coping with Asthma

If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.

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