Environmental Engineering Reference
In-Depth Information
change, or the predation of warfare and civil
strife, are now crumbling under the attack of acid
rain. The treasures of ancient Greece and Rome
have probably suffered more damage in the last
50 years than they did in the previous 2,000-
3,000 years (Park 1987). On the great cathedrals
of Europe—such as those in Cologne, Canterbury
and Chartres—the craftsmanship of medieval
stone masons and carvers may now be damaged
beyond repair (Pearce 1982a; Park 1987). Few
buildings in the industrialized regions of the
world are immune, and damage to the Taj Mahal
in India from sulphur pollution may be only the
first indication that the problem is spreading to
the developing world also (Park 1987). The
faceless statues and crumbling cornices of the
world's famous buildings receive most publicity,
but less spectacular structures may provide
important information on the rate at which
damage is occurring and its relationship to acid
emissions. In the United States, for example,
researchers investigating the effects of acid rain
on building materials have used the standardized
marble gravestones in national military
cemeteries, as controls in their field studies (Anon.
1984).
The chemical processes involved in acid rain
attacks on the built environment are essentially
the same as those involved in the natural
environment, but there are some differences in
the nature and provenance of the acidity. Damage
in urban areas is more often associated with dry
deposition than with wet, for example (Park
1987). Acidic particles falling out of the
atmosphere close to their source land on
buildings, and, once moisture is added, corrosion
begins. Damage is usually attributed to
deposition from local sources, such as the smelters
or power stations commonly found in urban
areas, with little of the long range transportation
associated with acidification in the natural
environment. However, in cities with little
industrial activity, such as Ottawa, Canada, most
of the damage will be caused by wet deposition
originating some distance upwind (LaBastille
1981), and the same probably applies to acid
corrosion of isolated rural structures (Park 1987).
Since the various Clean Air Acts introduced in
Europe and North America in the 1960s and
1970s had their greatest impact on urban
pollution levels, it might be expected that the
effects of acid rain on the built environment
would be decreasing. There is some indication
that this is so, but there appears to be a time lag
involved, and it may be some time before the
reduction in emissions is reflected in a reduction
of acid damage to buildings and other structures
(Park 1987).
ACID RAIN AND HUMAN HEALTH
The infamous London Smog of 1952 developed
as a result of meteorological conditions which
allowed the build-up of pollutants within the
urban atmosphere. Smoke, produced by domestic
fires, power stations and coal-burning industries,
was the most obvious pollutant, but the most
dangerous was sulphuric acid, floating free in
aerosol form or attached to the smoke particles
(Williamson 1973). Drawn deep into the lungs,
the sulphuric acid caused or aggravated breathing
problems, and many of the 4,000 deaths
attributed to the smog were brought about by
the effect of sulphuric acid on the human
respiratory system (Bach 1972). Although the
Clean Air Acts of the 1960s and 1970s, along
with such developments as the tall stacks policy,
reduced the amount of sulphur compounds in
urban air, recent studies in Ontario and
Pennsylvania have indicated that elevated
atmospheric acidity continues to cause chronic
respiratory problems in these areas (Lippmann
1986).
The acid rain which causes respiratory
problems is in a dry gaseous or aerosol form,
and mainly of local origin. It is therefore quite
different from the far-travelled wet deposition
that has caused major problems in the natural
environment. There is, as yet, no evidence that
wet deposition is directly damaging to human
health, but, because of its ability to mobilize
metals, it may have important indirect effects
(Park 1987). For example, in Norway the intake
of aluminium in acidified water has been linked
