Geoscience Reference
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coarse mode, nitrate is usually in the coarse mode. The
high coarse mode nitrate concentration in Figure 5.13
was most likely due to acidification of sea spray and
soil dust particles.
Other (2.31)
Forest fires (3.60)
Chemical production
(6.68)
Agricultural waste burning (1.47)
Savannah burning (5.33)
Manure
management
(21.3)
5.3.2.1.5. Sulfuric Acid.
Gas-phase
sulfuric acid
[H
2
SO
4
(g)] is condensable due to its low saturation
vapor pressure. Once it condenses, it does not read-
ily evaporate, so it is
involatile
.Assulfuric acid con-
denses, water vapor molecules simultaneously hydrate
to it. Thus, condensation of sulfuric acid produces a
solution of sulfuric acid and water, even if a solution
did not preexist.
Once condensed irreversibly, sulfuric acid dissoci-
ates reversibly. Condensation and dissociation are rep-
resented by
Manure
use (12.8)
Soil emissions (46.5)
Figure 5.14.
Percentage of the 2005 worldwide
ammonia gas emissions of 48.389 Tg-NH
3
(g) from
different sources. “Other” includes electricity and
heat production (0.21 percent), other energy
industries (0.023 percent), manufacturing industries
and construction (0.31 percent), road transport
(0.95 percent), residential (0.086 percent), fugitive
dust emissions from solid fuels (0.0047 percent),
mineral production (0.077 percent), grassland fires
(0.61 percent), and other waste handling (0.037
percent). Data from EC-JRC/PBL (2010).
HSO
4
H
+
H
2
SO
4
(g)
→
H
2
SO
4
(aq)
+
Sulfuric
Dissolved
Hydrogen
Bisulfate
acid gas
sulfuric acid
ion
ion
2H
+
SO
2
−
4
+
(5.10)
Hydrogen
Sulfate
ion
ion
The first dissociation [producing the
bisulfate ion
(HSO
4
−
)] occurs when the pH exceeds -3, so sulfu-
ric acid is a strong acid. The second dissociation [pro-
ducing the
sulfate ion
(SO
4
2
−
)] occurs when the pH
exceeds
(NH
4
+
)by
NH
3
(g)
NH
3
(aq)
(5.11)
2, so the bisulfate ion is also a strong acid.
Condensation of sulfuric acid occurs most readily
over the particle size mode with the most surface area,
which is the accumulation mode. When sulfuric acid
condenses on coarse mode sea spray drops, it displaces
the chloride ion as hydrochloric acid to the gas phase.
When it condenses on soil dust particles, sulfuric acid
displaces the carbonate ion as carbon dioxide to the
gas phase. In a competition with nitrate, sulfuric acid
also displaces the nitrate ion as nitric acid to the gas
phase.
+
Ammonia
Dissolved
gas
ammonia
NH
4
H
+
NH
3
(aq)
+
(5.12)
Dissolved
Hydrogen
Ammonium
ammonia
ion
ion
Because the ammonium ion is positively charged, it pri-
marily enters particles that have an abundance of nega-
tively charged ions (anions) in order to maintain charge
balance. Particles that have an abundance of anions are
acidic and thus have a low pH. Acidic particles gen-
erally contain sulfate, nitrate, or chloride, which are
all anions. Particles that are basic (have a high pH),
often contain significant amounts of sodium, potas-
sium, calcium, or magnesium, which are all cations.
Thus, the ammonium ion generally enters particles that
have an abundance of anions but not particles that
have an abundance of cations
.Because sea spray and
soil particle solutions contain high concentrations of
cations, and thus have a high pH, ammonia rarely enters
these particles. An exception is when high concentra-
tions of sulfate or nitrate ions are also present (e.g.,
Figure 5.13).
5.3.2.1.6. Ammonia.
Ammonia gas
[NH
3
(g)] is
emitted during bacterial metabolism in domestic and
wild animals and their waste, humans, fertilizers, natu-
ral soil, and the oceans. It is also emitted during biomass
burning (forest fires, savannah and grassland burning,
outdoor agricultural waste burning), biofuel burning,
and fossil fuel combustion. Figure 5.14 summarizes
the relative source contributions to worldwide ammo-
nia emissions in 2005.
When ammonia dissolves in water, it combines
with the hydrogen ion to form the
ammonium ion
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