Geoscience Reference
In-Depth Information
0.3
0.3
Central Los Angeles
August 28, 1987
San Bernardino
August 28, 1987
O
3
(g)
0.2
0.2
NO(g)
NO
2
(g)
NO
2
(g)
O
3
(g)
0.1
0.1
NO(g)
0
0
0
6
12
18
24
0
6
12
18
24
Hour of day
Hour of day
(a)
(b)
Figure 4.13.
Evolution of NO(g), NO
2
(g), and O
3
(g) mixing ratios in (a) central Los Angeles and (b) San
Bernardino on August 28, 1987. Central Los Angeles is closer to the coast than is San Bernardino. A sea breeze
sends primary pollutants, such as NO(g), from the west side of the Los Angeles Basin (i.e., central Los Angeles)
toward the east side (i.e., San Bernardino). As the pollutants travel, organic peroxy radicals convert NO(g) to
NO
2
(g). Photolysis of NO
2
(g) produces atomic oxygen, which forms ozone, a secondary pollutant.
include evaporative emissions and incomplete combus-
tion. Evaporative emissions originate from oil fields,
refineries, gas stations, automobiles, petroleum product
production, solvent production and use, and painting,
among other sources. Incomplete combustion occurs in
power plants, factories, homes, incinerators, and auto-
mobiles.
Table 4.1 shows the rates of primary pollutant gas
emissions in the Los Angeles Basin and California for
several species and groups of chemicals in 2005. Carbon
dioxide is the most abundantly emitted anthropogenic
gas. It is not reactive chemically, but its local emis-
sions result in the formation of
carbon dioxide domes
overLos Angeles and other cities that warm the air
locally. The warmer air evaporates water, and both the
water and higher temperature increase the rate of ozone
formation in polluted air (Section 12.5.6). Carbon
monoxide is the second most abundantly emitted gas. It
increases ozone slightly in urban air but is more impor-
tant for producing ozone in the background troposphere.
Methane is the most abundantly emitted organic gas in
urban areas; however, due to its long chemical life-
time, it has little direct chemical impact on local ozone
production. However, it can enhance local ozone by
forming a
methane dome
,which is similar to a carbon
dioxide dome. Methane domes enhance local tempera-
tures and thus local ozone.
Of the ROGs, hexane, butanol, pentane, toluene,
xylene, butane, ethane, ethene, various aldehydes, and
benzene are generally emitted in the greatest abundance.
NO
x
(g) emission rates are five to ten times higher than
are SO
x
(g) emission rates, indicating that Los Angeles
and California are more susceptible to nitric acid depo-
sition than to sulfuric acid deposition problems (Chapter
10). Sulfur emission rates in California are low relative
to those in many other regions worldwide. Ammonia
emission rates are lower than are sulfur emission rates
in California, but they are still high enough to produce
ammonium sulfate and ammonium nitrate aerosol par-
ticles (Chapter 5).
Table 4.2 shows the approximate percentage emis-
sion of several gases by source category in Los Ange-
les. Emissions originate from point, area, and mobile
sources. A
point source
is an individual pollutant
source, such as a smokestack, fixed in space. A
mobile
source
is a moving individual pollutant source, such
as the exhaust of a motor vehicle or an airplane. An
area source
is an area, such as a city block, agricultural
Table 4.1.
Gas-phase emissions (tonnes/day) in
Los Angeles Basin and California, 2005
Substance
Los Angeles California
Carbon dioxide [CO
2
(g)]
693,000
1,450,000
Carbon monoxide [CO(g)]
4,740
13,900
Methane [CH
4
(g)]
479
1,975
Total ROGs
1,070
3,240
TotalNO
x
(g) as NO
2
(g)
1,460
3,840
TotalSO
x
(g) as SO
2
(g)
162
781
Ammonia [NH
3
(g)]
70
553
ROG, reactive organic gas.
Source
:Jacobson and Ginnebaugh (2010).
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