The Greenhouse Effect and Global Warming - Air Pollution and Global Warming: History, Science, and Solutions - page 298

250

8.07

Polluted surface air

Stratospheric air (25 km)

8.065

200

299.15 K

8.06

298.15 K

150

8.055

220.05 K

100

221.55 K

8.05

50 299.15 K

8.045

Clean surface air

298.15 K

0 8.04

0 0.01 0.02 0.03 0.04

2 10 -6 6 10 -6 1 10 -5 1.4 10 -5

(a) Water vapor mixing ratio (fraction) (b) Water vapor mixing ratio (fraction)

Figure 12.30. Ozone mixing ratio as a function of water vapor mixing ratio under (a) polluted and clean surface
conditions and (b) stratospheric conditions at 25 km. For each condition, two temperatures are shown, a base
temperature (blue line) and a temperature 1 K higher than the base temperature (red line). For clean air
surface conditions, the two lines are nearly on top of each other. Results were obtained considering chemistry
alone over (a) a 12-hour daytime period and (b) a 36-hour period. From Jacobson (2008a).

heat stress-related health problems, including mortal-
ity, more than they do in milder climates (e.g., Medina-
Ramon and Schwartz, 2007). People currently living in
cold climates are likely to experience little or no heat
stress. Heat-related health problems, such as heat rash,
heat stroke, and death, generally affect the elderly and
those suffering from illnesses more than they affect the
general population.

In addition, soot particles containing black carbon are
dangerous to health. However, global warming itself
affects the concentrations of health-affecting air pollu-
tants, such as ozone and particulate matter.
Because greenhouse gases are long lived, they even-
tually become well mixed in the global atmosphere.
Near emission sources, such as over cities, though,
greenhouse gas mixing ratios are higher than they are
in the global atmosphere because emission rates over
cities exceed dilution rates to the global environment.
In the case of carbon dioxide, the high mixing ratio
over a city is referred to as a carbon dioxide dome .
CO 2 (g) domes enhance the formation rate of air pollu-
tion (Jacobson, 2010a). Methane can also form a dome
overacity and have a similar impact.
Both well-mixed greenhouse gases away from cities
and carbon dioxide domes over cities increase not only
tropospheric temperatures, but also water vapor due
to evaporation caused by the higher temperatures. If
chemistry alone is considered, higher temperatures and
higher water vapor both independently increase surface
ozone in polluted air but cause little change in surface
ozone in clean air (Jacobson, 2008a), as illustrated in
Figure 12.30a.
To illustrate, a 1 K rise in air temperature increases
ozone by about 6.7 ppbv at 200 ppbv ozone, but the
same temperature rise increases ozone by only about 0.1
ppbv at 40 ppbv ozone when only chemistry's effects on
ozone are considered. The reason that high temperatures
increase ozone more in polluted air than in clean air is
the fast increase in the thermal dissociation of PAN to

12.5.5. Changes in Disease
Increases in land precipitation as a result of global
warming increase the populations of mosquitoes and
several other insects that carry disease. Furthermore,
because malaria is not transmitted below a certain tem-
perature, rising temperatures will increase the spread of
malaria to places previously too cold for it to thrive,
including higher latitudes and mountains. Similarly,
influenza occurs year-round in the tropics because of
the warm climate. Higher year-round temperatures at
higher latitudes will likely lengthen the flu season. In
addition, drought in rural areas may drive populations
toward cities, where diseases transmit more readily than
in rural areas.

12.5.6. Changes in Air Pollution
Most major greenhouse gases, including carbon diox-
ide, methane, nitrous oxide, and CFCs, do not cause
direct harmful human health problems at normal ambi-
ent mixing ratios (Section 3.6). However, other green-
house gases, such as ozone and carbon monoxide, do.