Environmental Engineering Reference
In-Depth Information
Current concern over acid rain is not with the
naturally produced variety, but rather with that
which results from modern industrial activity.
Technological advancement in a society often
depends upon the availability of metallic ores,
which can be smelted to produce the great volume
and variety of metals needed for industrial and
socio-economic development. Considerable
amounts of SO
2
are released into the atmosphere
as a by-product of the smelting process,
particularly when non-ferrous ores are involved.
The burning of coal and oil, to provide energy
for space heating or to fuel thermal electric power
stations, also produces SO
2
. The continuing
growth of transportation systems using the
internal combustion engine—another
characteristic of a modern technological society—
contributes to acid rain through the release of
NO
X
into the atmosphere.
Initially, the effects of these pollutants were
restricted to the local areas in which they
originated, and where their impact was often
obvious. The detrimental effects of SO
2
on
vegetation around the smelters at Sudbury
(Ontario), Trail (British Columbia), Anaconda
(Montana) and Sheffield (England) have long
been recognized, for example (Garnett 1967;
Hepting 1971). As emissions increased, and the
gases were gradually incorporated into the larger
scale atmospheric circulation, the stage was set
for an intensification of the problem. Sulphur
compounds of anthropogenic origin are now
blamed for as much as 65 per cent of the acid
rain in eastern North America, with nitrogen
compounds accounting for the remainder
(Ontario: Ministry of the Environment 1980).
In Europe, emission totals for SO
2
and NO
X
are
commonly considered to split closer to 75 per
cent and 25 per cent (Park 1987). Since the early
1970s, however, declining SO
2
emissions and a
growing output of NO
X
have combined to bring
Figure 4.1
The pH scale:
showing the pH level of
acid rain in comparison
to that of other common
substances
