Geology Reference
In-Depth Information
Northern Hemisphere. The natural sources include volcanoes, plants,
soil and biogenic activity in the oceans.
5
In terms of photochemistry the
major sulfur oxide, sulfur dioxide (SO
2
) does not photodissociate in the
troposphere (cf. NO
2
), i.e.
SO
2
(X
1
A
1
)
þ
hn(240
o
l
o
330 nm)
SO
2
(
1
A
2
,
1
B
1
)
-
(2.64)
SO
2
(X
1
A
1
)
þ
hn(340
o
l
o
400 nm)
SO
2
(
3
B
1
)
-
(2.65)
The oxidation of sulfur compounds in the atmosphere has implications
in a number of different atmospheric problems such as acidification,
climate balance and the formation of a sulfate layer in the stratosphere,
the so-called Junge layer. By far the largest sulfur component emitted
into the atmosphere is SO
2
. Figure 19 shows the spatial distribution of
SO
2
emissions in 1980 and 2000 from EMEP.
34
In Europe, the source
regions for SO
2
are quite apparent, the so-called black triangle region
(southern Poland, eastern Germany and the northern part of the Czech
Republic) are the largest sources of anthropogenic sulfur pollution.
There are a number of other large emission sources including central
UK and the Kola Peninsula, also apparent in Figure 19. The absolute
maximum in emissions is in southern Italy around Sicily where the
largest single source of both natural, the volcano Mt. Etna, and anthro-
pogenic SO
2
is found. SO
2
can be detected from space-borne sensors
35
as
a product of volcanic activity and fossil fuel burning. Figure 19 also
illustrates another interesting point in that over much of Europe between
1980 and 2000 there has been a decrease of 1000 ton or more owing
to legislative limits. Interestingly, with decreasing land emissions the
importance of ship emissions has increased (from 5% to 16% of total
European SO
2
emissions).
The atmospheric oxidation of SO
2
can take place by a number of
different mechanisms, both homogeneously and heterogeneously in the
liquid and gas phases (see Figure 20). The gas-phase oxidation of SO
2
, viz
SO
2
þ
OH
þ
M
-
HSO
3
þ
M
(2.66)
HSO
3
þ
O
2
-
HO
2
þ
SO
3
(2.67)
SO
2
þ
H
2
O
þ
M
-
H
2
SO
4
(2.68)
can lead to the formation of sulfuric acid, which owing to its relatively
low vapour pressure can rapidly attach to the condensed phase such as
