The Greenhouse Effect and Global Warming - Air Pollution and Global Warming: History, Science, and Solutions - page 306

CO 2 (g) ( 1), controlling both FS and BSG causes

greater cooling than controlling the same unit contin-
uous emission of CH 4 (g) or CO 2 (g) over either 20- or
100-year time frames.

= the warming due to BC with lesser warming or cooling

due to other components results in a decrease in the
STRE of FS and BSG relative to BC alone in FS and
BSG.
In sum, FS causes more warming per unit emission
than does BSG, and both cause more warming per unit
emission than do methane or carbon dioxide. However,
BSG causes more than eight times the mortality (caus-
ing more than 1.5 million premature deaths per year)
than FS because, although both result in particulate mat-
ter, the most deadly component of air pollution, BSG
is emitted in much more densely populated regions of
the world. Both FS and BSG cause hundreds of thou-
sands of times greater mortality per unit mass emission
than do CO 2 (g) orCH 4 (g). However, CO 2 (g) causes the
greatest overall warming of climate among the chemi-
cals.
Thus, controlling soot emissions slows global warm-
ing and reduces human mortality faster than does any
other mechanism considered .Due to the speed of its cli-
mate response, controlling soot may be the only method
of preventing the elimination of the Arctic sea ice, which
may occur within two to three decades. However, also
controlling CO 2 (g) and CH 4 (g) is essential for stabiliz-
ing global temperatures, particularly because CO 2 (g)
is the largest component of global warming .

Example 12.4
If a diesel vehicle emits 99 g-CO 2 (g) km −1 and
the Euro 5 particulate matter emission standard
of 5 mg-FS-C km −1 (where FS is fossil fuel soot),
estimate the total CO 2 (g)-equivalent [CO 2 (g)-eq]
emissions of the exhaust over 20 and 100 years.
CO 2 (g)-eq emissions are those of CO 2 (g) plus of
other components of global warming, each multi-
plied by the ratio of the global warming potential
of the component relative to that of CO 2 (g). This
parameter allows different sources of pollution
to be evaluated relative to each other in terms
of their potential contribution to global warm-
ing. Do the same calculation for a gasoline vehi-
cle that emits 103 g-CO 2 (g) km −1 and 1 mg-FS-C
km −1 .Whichvehicle emits more CO 2 (g)-eq over
each period?

Solution
Multiply the 20- and 100-year STREs for FS from
Table 12.6 by the change in FS-C emissions and
add the result to the CO 2 (g) emissions to obtain
the CO 2 (g)-eq emissions from the vehicle. For
example, the low estimate of the 20-year CO 2 (g)-
eq emissions for diesel is 99 g-CO 2 (g) km −1

12.7. Summary
In this chapter, the greenhouse effect; historical tem-
perature trends; and causes, characteristics, effects, and
regulatory control of global warming are discussed.
Greenhouse gases selectively absorb thermal-IR radi-
ation but are transparent to visible radiation. Without
the presence of natural greenhouse gases, particularly
water vapor and carbon dioxide, the Earth would be
too cold to support higher life forms. Global warm-
ing is the increase in the Earth's temperature above
that caused by natural greenhouse gases. Greenhouse
gases that contribute the most to global warming are
carbon dioxide, methane, and nitrous oxide. The sec-
ond most important component of near-surface global
warming, after carbon dioxide and before methane, may
be particulate BC, which absorbs solar and thermal-IR
radiation. Anthropogenic emissions and ambient lev-
els of greenhouse gases and BC have increased since
the mid-1800s. Air temperatures have also increased.
Although temperatures throughout Earth's history have
frequently been higher than they are today, the cur-
rent rate of temperature increase is higher than dur-
ing any time since deglaciation at the end of the

+

0.005 g-CO 2 (g) km −1 2,400 g-CO 2 (g)-eq g −1 - ×

111 g-CO 2 (g)-eq km −1 .
Using this methodology, the overall ranges are
Diesel: 111-118 g-CO 2 (g)-eq km −1 over
20 years and 105-108.5 g-CO 2 (g)-eq km −1
over 100 years.
Gasoline: 105.4-106.8 g-CO 2 (g)-eq km −1 over
20 years and 104.2-104.9 g-CO 2 (g)-eq km −1
over 100 years.

FS-C =

Thus, this gasoline vehicle emits less CO 2 (g)-
eq emissions than the diesel vehicle. However,
both vehicles emit significant levels of CO 2 (g)-eq
compared, for example, with an electric vehicle,
which emits 0 g-CO 2 (g)-eq km −1 from the vehicle
itself.

Table 12.6 indicates that the 20- and 100-year STREs
of black carbon alone in FS and BSG is greater than is
that of FS or BSG as a whole, respectively. The reason
is that BC is a much stronger warming agent than are
the other materials in each FS and BSG, so averaging