Motion of the atmosphere may transport pollutants far from their source,
often crossing national boundaries. The associated pollution can take the
form of isolated, extreme events, or longer-term, lower level pollution.
Although acute events may be the most spectacular, long-term pollution
often gives rise to high cumulative loads, and can be very serious.
There are many possible examples of acute long-distance pollution
events. Among most severe in recent years are
500-600 oil wells were set alight by the retreating Iraqi army during
Gulf War in February 1991. This provided the atmosphere with the largest
loading of anthropogenically-produced aerosols in a single event. The
Iraqi strategy of mining Kuwait's oil wells was announced beforehand, and
the effects of the fires were predicted, some alarmist, some not. The most
alarming predictions were made by Richard Turco of UCLA: he argued that
3 million tonnes of smoke would be produced, covering 100 million km2
(20% of earths surface). He argued that heating of the plume by fires and
sunlight would cause lofting, raising aerosols into the stratosphere, shading
the earth and causing cooling. This was a development of Turco's ‘Nuclear
winter’ scenario. John Cox, (a chemical engineer & CND president) suggested
that the monsoon may be affected. The Asian monsoon arises because the
land in Indian subgcontinent warms more in summer than the surrounding
ocean. The warm air rises, sucking in moist oceanic air. The oil smoke
was predicted to reduce the temperature gradient between land and sea,
thus shutting down the monsoon. The UK Met Office disagreed, as did many
other atmospheric scientists.
Reality : The peak oil burn rate was around 4 million barrels per day in March 1991: this is almost 10% of the World's daily oil consumption. The smoke plumes extended up to 1200 km, with a maximum plume area of 11,000 km2 (an area the size of Kuwait itself). Typical particulate mass densities of 0.5 to 1 g m-3. Smoke only rose to 5,000 m: ie. the lower half of troposphere: it did not rise into the stratosphere. The composition of plume consisted of smoke (soot particles), SO2, NOx, unburnt hydrocarbons, and CO2 (3% of total annual emissions). Absorption of energy by the plume was low due to its high density, therefore the predicted lofting did not occur. The plumes were low, and fires were rapidly extinguished. Most of the plume confined to region, although longer distance transport did occur.
The effects, however, were devastating. The downward flux of shortwave radiation was reduced from 800 W m-2 to zero below centres of plumes. Daytime temperatures were reduced by up to 10°C. Mean monthly temps in region (March- September) were reduced by 0.8-2.4°C, and record lows occurred in July and August. Temperature reductions of 1-2°C were observed up to 2000 km from Kuwait. Black snow fell in the mountains of Pakistan, and Kashmir, 2600 km distant. Soot from the oil fires was detected over Japan, North America, and Hawaii several months later. Unburnt oil fell in drops from the sky within tens of km of the burning wells, leaving a sticky coating on buildings, crops, water reservoirs, livestock, and people, and particulates caused acute and chronic health problems, especially bronchitis and breathing problems among children and the elderly. Acute problems included headaches and nausea. Acid rain fell in neighbouring countries, with pH levels of 3.0-3.6. Thus, although global effects (including monsoon effects) were insignificant compared to the worst predictions, the local effects were huge. The dramatic disaster predictions therefore make the reality less serious, although it was in all respects a major air pollution disaster. This underlines the dangers of environmentalists overstating their case, and weakening their credibility. The reality is serious enough.
http://climate.gsfc.nasa.gov/~cahalan/KuwaitFires/KuwaitFires.html
Some images and a bibliography about the Kuwait oil fires
During September - November 1997, the usual annual burning of vegetation
in Kalimantan (Borneo), Sumatra and Irian Jaya (New Guinea) combined with
severe drought associated with a strong El Nino event resulted in extensive
fires. The fires caused vast smoke plumes and associated photochemical
smogs, that covered much of the region, including parts of the neighbouring
countries of Malaysia and Singapore, and affecting up to 70 million people.
By late september, 15,000 Malaysians and 45,000 Indonesians (mostly elderly
and children) had been treated for smog-related illnesses. An Indonesian
airliner crashed, partly due to poor visibilty, killing 234 people.
The burning is due to 3 factors:
This unprecedented demand for land combined with one of most intense
droughts on record, and led to extensive fires. The drought was caused
by reversal of the usual circulation patterns in the Pacific region - an
El Nino event - and consequent failure of the usual monsoon rains. The
rains came late (Mid November) and ended early.
A similar problem occurred during 1982-1983 El Nino. Recent El Ninos
have been especially severe and prolonged: is this a symptom of global
warming?
Internet sources:
Many internet sites contain information on the fires and associated pollution. Among the most useful are:
http://toms.gsfc.nasa.gov/aerosols/smoke01.html
(Day-by-day images of smoke extent: look up Aerosols: you can see the
global distribution of atmospheric aerosols for any requested day. Looking
at the images for September 1998 shows the Indonesian fires clearly, plus
burning elsewhere in the Tropics.
http://www.pmel.noaa.gov/tao/elnino/el-nino-story.html
Nice page explaining how El Nino works, with links to lots of other
resources
Acid Rain
One of the most important long-range air pollution issues is the problem of acid rain. Acids can be precipitated as snow or dew, as well as rain. Also, acid-forming compounds can be precipitated as dry gases or adhering to the surfaces of solid particles, such as soot (dry deposition). So, strictly speaking, we should refer to acid precipitation, although often the term acid rain is used to cover all kinds of wet and dry deposition. Acid rain is due to the widespread dispersion of acidic aerosols (Nitrogen and Sulphur compounds) in unstable or windy conditions. Acid rain is the regional equivalent of acidic air pollution (sulphurous or photochemical smogs) from cities or industrial complexes. Acid rain is much more dilute than local acidic air quality crisis levels, and its effects are more complex.
Acids; a definition:
Acids are molecules that release hydrogen ions into solution.
Hydrogen ions consist of a single free proton without an
electron: they therefore have positive charge and are written H+.
Hydrogen ions are very reactive: they are able to combine with a wide range
of substances, altering their chemistry. Acids release hydrogen ions, increasing
the hydrogen ion concentration in a solution, and increasing its tendency
to react with other substances.
Acidity is measured by the concentration of hydrogen ions in a solution on the pH scale (potential hydrogen). The scale is negative: lower numbers relate to higher acidity, and logarithmic: a change of one point on the pH scale means a tenfold change in Hydrogen ion concentration. Thus an acid with a pH of 4 has a hydrogen ion concentration ten times that of an acid with pH 5.
Distilled water has a pH of 7, and is neutral. Substances with pH> 7 are alkaline, and those with pH < 7 are acidic. All rainwater is slightly acidic (pH ~5.5) due to the presence of naturally-occuring acids produced by biological and volcanic processes, thunderstorms, and the absorption of CO2 by atmospheric water (weak carbonic acid). This weakly acidic rain participates in natural processes: the return of nitrogen and sulphur to soil helps maintain nutrient levels, and causes the weathering of limestone.
Human activities increase acidity, mainly by the input of SO2
and NOx into the atmosphere. These compounds form Nitric acid (HNO3
or H+ and NO3-), and sulphurous and sulphuric
acids (H2SO3 or H+ and HSO3-
and H2SO4 or H+ and HSO4-)
when they dissolve in water. Sulphur/ Nitrogen compounds account for 65/35%
of anthropogenic acid precipitation in USA and 75/25% in Europe. The European
trend is tending more toward US values (cleaner power stations and increasing
car use). The main polluters are the industrialized nations of N. America
and W.Europe, but E. Europe, Japan and China are also major contributors.
SO2 output in N. America and Europe peaked in 1970s/ early 1980s
and has declined since, but NOx continues to rise (vehicles). SO2
outputs remaining high or increasing in E. Europe and China (China’s economic
growth is largely fuelled by sulphurous coal). Problems also locally very
high in Third World cities.
Acid Rain increased partly due to the response to earlier acid smog problems. One of the responses to urban smogs was to introduce a Tall Stacks policy, higher stacks were built in power stations and factories to prevent pollutants from accumulating locally. In response to the Clean Air Acts, the former UK Central Electricity Generating Board (CEGB) erected 200m stacks at its generating stations in the1970s. The USA followed a similar policy, and by 1977 at least 20 stacks were > 300m high. A 400m superstack was erected at the Nickel smelter in Sudbury, Ontario (1972). These undoubtedly reduced local smog problems, but caused pollutants to remain in the atmosphere longer, increasing the areas affected and increasing the acidity of cloud droplets (though they tended to be more dispersed) because of the longer time available for reactions to be completed before deposition. There was consequently a significant increase in the geographical extent of problems of acid deposition.
The effects of acid precipitation depend on water chemistry in the areas where it falls. In turn, this reflects
Pollutants cross national boundaries, and there is thus a need for international
cooperation in pollution control. The rapid industrialization of China
is fuelled by sulphur-rich coal, and clean technologies are slow to be
introduced due to cost. Downwind pollution is severly affecting Japan,
and it is feared that the effects on forests will be as bad as in Europe.
Effects of acid rain
Vegetation damage:
Effects on vegetation may be direct due to acid particles coming
into contact with leaves, or indirect, via soils and groundwater.
Vegetation can concentrate acids: dry deposition occurs on leaves, and
acids are then washed off into the soil. This acidity affects soil processes:
disturbing nutrient cycles, interfering with bacterial activity; leaching
nutrients, and mobilizing toxic metals (especially aluminium (Al), copper
(Cu), iron (Fe), lead (Pb), zinc (Zn), mercury (Hg)). The released metals
then enter groundwater and lakes. In combinantion, the effects of acidity
cause leaf dieback, beginning with the crown and spreading to the whole
tree, giving it a skeletal appearance. In Europe, the symptoms were recognized
in 15 countries by mid-1980s. Forest damage is known in Germany as Waldsterben
(‘Forest Death’). 1500 hectares of Bavarian forest were dead by the early
1980s; and an estimated 50% of trees in Germany showed some damage by 1990.
Other European and Eastern European countries are also suffering. In North
America, 80% of maple trees in Quebec show damage.
Role of acid rain in damage has been questioned, as natural factors can also cause damage (e.g. water-table changes, insects, fungi). However, man-made and natural factors are not mutually exclusive. The multiple stress hypothesis conveys the idea that acid rain can make trees more susceptible to other stressors, and thus more likely to die or suffer due to a dry season or fungal attack.
Lakes:
Acidification of lake water, and associated increase of toxic metals,
is a major problem in N. America and Europe (especially Scandinavia). Acid
lakes have low nutrient levels, and high concentrations of Al, Mg, Mn,
Zn and Pb. Al is especially problematic. In lakes with pH below 5.6, Al
is usually sufficiently concentrated to kill fish. Acidification also causes
changes to ecosystem structure: acid-tolerant species thrive (Sphagnum,
green algae, water boatmen) and others perish.
Built environment:
Limestone is a common building material, which is attacked by acidic
water. Calcium and Magnesium carbonates react with sulphuric acid, and
form soluble sulphates. The sulphates are washed out, weakening the stone
and destroying fine decoration. Water in such solutions also evaporates,
precipitating calcium and magnesium sulphate crystals, which cause disintegration
of the surrounding stone. The buildings of ancient Greece & Rome have
suffered more damage in the last 50 yr than in previous 2000. Damage has
also been done to the great Medieval cathedrals. Even the Taj Mahal has
suffered (minor) damage from local sulphur pollution.
Human Health:
Human health problems are less immediately obvious than for acid smogs
(due to the lesser concentrations of acid). However, there ay be indirect
effects due to release of metals such as Al . In Scandinavia, kidney problems
(renal failure) have been attributed to high concentrations of Al in drinking
water.
Previous solutions to acid smogs (tall stacks) merely passed on
the problem. Two other types of solution can be employed:
Alleviating effects
Acidified lakes can be neutralised by the addition of powdered lime
(CaCO3). This buffers acidity, increasing pH, and allowing ecosystem re-establishment.
In 1973: several lakes near Sudbury, Ontario were treated. Acidity returned
to normal and nutrient levels increased, although Cu and Ni remained at
toxic levels at lakes closest to plant. In Sweden over 3,000 lakes have
been limed since mid-1970s. The results are encouraging: the lower organisms
recover first (plankton) followed by invertebrates, amphibians and fish.
This is, however, a temporary measure (similar to taking antacid tablets
for indigestion). The problem will return in 3-5 yr if acid loading continues.
Liming only tackles consequences, not causes.
Controlling emissions
See Lecture
2
Internet resources:
http://www.epa.gov/airmarkets/acidrain/index.html
(homepage of the US Environmental Protection Agency acid rain program)