Urban Air Pollution - Air Pollution and Global Warming: History, Science, and Solutions - page 99

to the background troposphere, where they decay and
produce ozone. Carbon monoxide is another abundantly
emitted gas in urban air that escapes to the background
troposphere because of its long lifetime. CO(g) not only
produces ozone in the background troposphere, but is
also a chemical source of CO 2 (g). In the background
troposphere, the concentrations of ozone, nitric oxide,
and nitrogen dioxide are strongly coupled through the
photostationary-state relationship. In polluted urban air,
organics convert more NO(g) to NO 2 (g), increasing the
NO 2 (g):NO(g) ratio and thus ozone compared with the
photostationary-state ozone level. The use of ethanol
as a fuel may increase ozone production relative to
gasoline, particularly at low temperature. However, both
ethanol and gasoline, as well as other internal combus-
tion fuels, cause severe health problems. Such problems
can be eliminated most effectively by switching away
from internal combustion, as discussed in Chapter 13.

what do you believe is the reason for the differ-
ence?

4.7. If ozone mixing ratios are 0.16 ppmv and ROG
mixing ratios are 1.5 ppmC, what is the best regulatory
method of reducing ozone, if only the effects of NO x (g)
and ROGs on ozone are considered?

4.8. If NO x (g) mixing ratios are 0.2 ppmv and ROG
mixing ratios are 0.3 ppmC, what is the best regulatory
method of reducing ozone if only the effects of NO x (g)
and ROGs on ozone are considered?

4.9. If NO x (g) mixing ratios are 0.05 ppmv and ROG
mixing ratios are 1 ppmC, what would be the resulting
ozone mixing ratio if ROGs were increased by 1 ppmC
and NO x (g) were increased by 0.1 ppmv?
4.10. In Figure 4.13, why are ozone mixing ratios high
and nitric oxide mixing ratios low in San Bernardino,
whereas the reverse is true in central Los Angeles?

4.6. Problems
4.1. Calculate the photostationary-state mixing ratio of
ozone when p d =

4.11. Why don't aromatic gases, emitted in urban air,
reach the stratosphere to produce ozone?

0.01 s − 1 , 1,013 hPa, T = 298 K, J ≈ 4.12. What are the two fundamental differences

between ozone production in the background tropo-
sphere and in urban air?

10 − 14 cm 3 molec − 1 s − 1 , k 1 ≈ 1.8 × NO(g) = 180 ppbv,

and 76 ppbv. Perform the same calculation

under the same conditions, except

NO 2 (g) =

NO(g) = 9 ppbv and

4.13. If the hydroxyl radical did not break down ROGs,
would aromatics still be important smog producers?
What about aldehydes? Explain.

NO 2 (g) = 37 ppbv.

(a) Ignoring the constant temperature and photolysis
coefficient, which of the two cases do you believe
represents afternoon conditions? Why?
(b) If the NO(g) and NO 2 (g) mixing ratios were mea-
sured in urban air, and ROG mixing ratios were
much higher in the morning than in the afternoon,
do you believe that the morning or afternoon ozone
mixing ratio calculated by the photostationary-state
relationship would be closer to the actual mixing
ratio of ozone? Why?
4.2. Explain why the photostationary-state relationship
is a useful relationship for background tropospheric air
but less usefulforurban air.
4.3. Why does ozone not form at night?
4.4. Why does the hydroxyl radical not form at night?
4.5. Why are nighttime ozone mixing ratios always
nonzero in the background troposphere but sometimes
zero in urban areas?
4.6. If nighttime ozone mixing ratios in one location
are zero and in another nearby location are nonzero,

4.14. Why is CO(g), the most abundantly emitted gas
in urban air, not an important smog producer?
4.15. Why should PAN mixing ratios peak at about
the same time as ozone mixing ratios during the
day?

4.16. In terms of chemical lifetimes and by-products,
what are some of the costs and benefits of methanol and
ethanol as alternative fuels?

4.17. Write out a chemical mechanism for the produc-
tion of ozone from propane [C 3 H 8 (g)] oxidation by
OH(g).

4.18. Write out a chemical mechanism showing how
benzaldehyde [C 6 H 5 CHO(g)] can form ozone.
4.19. Explain the main differences between the effects
of ethanol (E85) and gasoline on ozone production
when the ROG:NO x (g) ratio in background air is (a)
low ( 8:1) and (b) high. Explain your answer in terms

of an ozone isopleth.

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