Acid Deposition Case Studies

THE CZECH REPUBLIC

Background Information

Since 1st January 1993, the Czech Republic has become a separate state along with Slovakia, both states being previously known as Czechoslovakia.

Key Facts on the Czech Republic

Population:
10.3 million (Dec 1999)

Size:
78 866km²

Capital:
Prague (1.2m population)

Neighbours:
Germany, Austria, Slovakia, Poland

Climate:
Four seasons, coldest January (-2°C), warmest July (20°C)

Average altitude:
450m above sea level

Air Quality:
Generally poor, particularly during winter months

Acid Deposition:
One of the highest acid deposition levels in Europe

Czech Republic, 2001

Source: The Perry-Castañeda Library Map Collection, The General Libraries, The University of Texas at Austin, Austin, TX 78713-8916, USA

Acidic Pollutant Emissions

The main acidic pollutants are sulphur dioxide and oxides of nitrogen and during 1998, the Czech Republic emitted 0.44 million tonnes of sulphur dioxide and 0.41 million tonnes of nitrogen oxides. This is a sizeable output considering the relatively small population of 10.3 million, although sulphur dioxide emissions have fallen by 76% since 1990. Emissions of nitrogen oxides have also been falling in the Czech Republic, by nearly half between 1990 and 1998. Nevertheless, air quality in Czech Republic is still considered to be a problem.

The Czech Republic is an important industrial nation in Europe with its main economic sector being industry, employing more than 2 million and generating 62% of national income. There are several heavily polluted areas within the Czech Republic, such that a large percentage of the population live in severely polluted air. In Prague, winter concentrations of sulphur dioxide and particulates are often more than twice the World Health Organisation (WHO) Air Quality Guidelines (AQG). At these times the long term guidelines set by WHO for exposure to these pollutants are exceeded.

The most polluted area of the Czech Republic is in northern Bohemia which stretches for 60km from Chutomov to Literomice (see map). Here, power stations are fuelled by lignite, otherwise known as brown coal, which has a high sulphur content and when burnt produces large quantities of sulphur dioxide. Additionally, because the coal has a low calorific value, large quantities are required to obtain the power. The low energy value of the coal also means that it has to be burnt near the mines. Hence the industrial areas are situated in the valley of the Ore Mountains where mining takes up almost 10 000 hectares of land.

The towns in the valleys of northern Bohemia are further troubled by temperature inversions which trap the pollutants in the cold air of the valley bottom. This prevents normal air currents from dispersing the pollutants. The towns become enveloped in a cold and smelly smog, whereas up on the hill tops the air is warm and clear. The valley is thus known as the Bohemian basin.

Acidic Pollutant Depositions

The Czech Republic also receives acidic pollutants from other countries, as shown in Table 3.1.

Table 3.1: Originating countries of sulphur deposition on Czech Republic

Total deposition of sulphur on the Czech Republic during 1998 was around 0.14 million tonnes (by weight of sulphur). When this is compared to the amount that is emitted in the Czech Republic (0.44 million tonnes of sulphur dioxide or 0.22 million tonnes of sulphur, 1998) it becomes apparent that much of the sulphur produced within the Republic is transported to other countries. Most of this pollution is exported to Poland, Germany, and the Russian Federation, as shown in Table 3.2.

Table 3.2. Selected countries receiving sulphur from the Czech Republic (1998)

The Czech Republic, along with other countries in the industrialised zone from Poland through to Germany, the Benelux countries to the UK, receive the highest levels of acid deposition in Europe. In the Czech Republic industrial sources of sulphur and nitrogen oxides account for the major emission sources, whilst in the UK for example vehicles are a more important source of nitrogen oxides due to much higher car ownership.

Effects of Acid Deposition on Forests

Around one third of the Czech Republic is covered in forest and so timber is a major economic resource. The high levels of acid deposition experienced over recent decades have had serious damaging effects on both broadleaf and coniferous trees in the Czech Republic. The European Forest Damage Survey results for 2000 show that 52% of all trees in the Czech Republic are classified as moderately to severely damaged (trees with more than 25% loss of leaves or needles). The trees most affected are Norway spruce (Picea abies) in the mountainous area of the country where soil acidification and acidic deposition have resulted in the loss of 100,000 hectares of forest.

Trees aged over sixty years are particularly vulnerable and all trees on the forested areas of the Ore mountains and other land over 800m altitude have been affected by sulphur dioxide. The trees are additionally stressed on occasion with extreme climatic conditions.

The problem of acidification was first observed by foresters in the 1960s and 1970s when individual spruces died and crown thinning of older trees became apparent. The damage is now spreading to the valleys and is also affecting deciduous trees. More resistant species of spruce such as Picea pungens are being planted where trees have died and other areas are being replaced by grassy meadows.

Effects of Acid Deposition on Water

Water supplies in many parts of the Czech Republic are already severely polluted as a result of poor sewage treatment, industrial effluent and artificial fertilisers. The severe soil acidification problems often lead to higher pH levels in groundwaters in the Czech Republic.

Surface water acidification can be expected when acid deposition levels are high and the bedrock is sensitive to acid deposition (i.e. there is little buffering capacity). Lakes and rivers in the mountainous Erzgebirge forested areas have been identified as acidic as a result of high acid deposition levels and sandy soils with low buffering capacity.

Effects of Acid Deposition on Buildings

Many of the buildings in the Czech Republic have become blackened by air pollutants and corrosion is occurring at faster rates than through normal weathering. In the capital city of Prague, there are more than 200 large emission sources in addition to small sources and motor vehicles which contribute around 56 000 tonnes of sulphur dioxide, 24 000 tonnes of nitrogen oxides and 24 000 tonnes of particulates to the city air each year. The highest concentrations of pollutants are recorded in the historical core of the city in the 'Old Town' due to a combination of factors including topography and emission source locations. This air pollution causes high economic losses through accelerated corrosion on buildings in Prague and other buildings in the Czech Republic.

Effects of Acid Deposition on Health

The human health effects from air pollution and acidification are evident in the Czech Republic. Since the 1960s, air pollution has become an increasing problem affecting health. During smog conditions, hospital admissions increase, most relating to respiratory diseases. Those most at risk are the young, the elderly and asthmatics.

Life expectancy and infant mortality appear to be affected in areas associated with high levels of air pollutants. In northern Bohemia high levels of air pollutants are associated with high numbers of bronchial diseases. During February 1993, winter smog conditions occurred in northern Bohemia and daily mean concentrations of 825µgm^-3 sulphur dioxide and 480µgm^-3 particulates were recorded. These levels exceed World Health Organisation AQGs by around 4 times indicating the severity of the air quality in this region.

Control and Policy

The Czech Republic are committed to reducing sulphur emissions through the 1994 UNECE Protocol 'Further Reduction of Sulphur Emissions'. This Protocol requires the Czech Republic to reduce sulphur emissions by 50% by the year 2000, 60% by 2005 and 72% by 2010 (all based on 1980 levels). To date, the country is on target to achieve this level of emissions reduction.

The Government has also introduced counter measures to reduce air pollution during smog conditions. These include limiting car use and the use of high quality coal in power stations at such times.

FINLAND

Key facts on Finland

Population:
5.2 million (1999)

Size:
304 529km²

Capital:
Helsinki (0.55 million population)

Neighbours:
Norway, Sweden, Russian Federation

Climate:
Temperate January (-10°C), July (15°C)

Land use:
Forest 65%, agriculture 8%, water 10%, other 17%

Altitude:
152m (average)

Air Quality:
Generally good, but potential conditions for winter smogs in cities where vehicles contribute large amounts of nitrogen oxides to the atmosphere

Acid Deposition:
Amongst the lowest acid deposition levels in Europe. Surface water acidification is a serious problem.

Source: The Perry-Castañeda Library Map Collection, The General Libraries, The University of Texas at Austin, Austin, TX 78713-8916, USA

Acidic Pollutant Emissions

The main acidic pollutants are sulphur dioxide and oxides of nitrogen, and during 1998 Finland emitted 0.09 million tonnes of sulphur dioxide and 0.25 million tonnes of nitrogen oxides (as NO2). Nitrogen oxides are hence the major acidifying pollutants in Finland and these emissions mainly arise from road transport. The air quality in Finland can be poor in the cities due to the number of vehicles although in the more rural areas there are few large industrial sources of air pollution. Emissions of both sulphurous and nitrous pollutants are falling in Finland but the reduction in nitrogen oxides is very slight as shown in Table 3.3.

Table 3.3: Emissions of Acidifying Air Pollutants in Finland

Around one third of total electricity in Finland is used in the paper and pulp industry which is an important industry within Finland.

Acidic Pollutant Depositions

Air pollutants deposited on Finland originate from other countries as well, as shown in Table 3.4.

Table 3.4: The Originating Countries of Sulphur and Nitrogen Deposition on Finland

Total deposition of sulphur on Finland during 1998 was around 0.12 million tonnes whereas the amount emitted in Finland was less (0.09 million tonnes sulphur dioxide or 0.045 million tonnes sulphur, 1998). This highlights that Finland receives more sulphur pollution than originates there. However, Finland exports a significant proportion of sulphurous and nitrous pollutants to other countries, mainly the Russian Federation and Sweden and to the Baltic Sea and Atlantic Ocean.

Finland does not generally experience high levels of acid deposition although when south westerly winds occur deposition levels increase as pollutants are transported from central Europe.

Effects of Acid Deposition on Forests

Although the level of acid deposition is less in Finland than in many other European countries, the areas of rocky and barren land with thin soils, plus the climate, make Finland particularly susceptible to damage from air pollution. With the economy of Finland being dependent upon forestry, air pollution is considered to be a serious problem. Forests cover 2.6 million hectares of Finland, of which 2 million hectares are productive forest.

Acid deposition is known to wash essential nutrients such as calcium, potassium and magnesium from soils, and aluminium which is normally bound in the soil may be released into ground water. Soil acidification may affect the health of trees.

In the 1995 Forest Damage Survey, 13% of all trees were classified as moderately to severely damaged (more than 25% loss of needles or leaves). Annual surveys have shown a decrease in trees in the moderate to severely damaged category since 1989 when 18% were recorded in this category.

The problem of acidification appears to be affecting older trees in northern Finland where the climate is also harsher. Norway spruce (Picea abies) trees in southern Finland have shown discolouration which significantly correlates with modelled air pollution depositions. Pollution sensitive beard lichens have also become sparser in the southern region which indicates the effects of air pollution.

Effects of Acid Deposition on Water

Water covers 10% of Finland and, relative to its size, Finland has more lakes than any other country.

Acidification studies in Finland have shown that freshwater acidification is a serious problem in this country. Lake pH values have fallen in three out of four lakes studied and approximately 10% of 1000 lakes studied were seriously affected. Acidification has been shown to gradually increase from 1915 to 1950, to rapidly increase between 1950 and 1980 and generally to have since remained unchanged, possibly due to reductions of pollutants in most European countries.

Some smaller forest lakes have become more acidic through acid deposition. No lakes in Finland have been found to be fishless but several have lost gastropods, lamellibranches and many crustacean species.

Spring snow melts, flushing acid waters into lakes and streams, have led to low stocks of fish in the acid lakes in southern Finland.

Effects of Acid Deposition on Buildings

Many of the buildings in the capital city of Helsinki and other towns and cities in the country are likely to experience accelerated corrosion due to the high levels of vehicle pollutants emitted from transport in urban areas.

Effects of Acid Deposition on Health

The human health effects from air pollution and acidification are not serious in Finland. However, in large urban areas such as Helsinki, concentrations of air pollutants may be sufficient, particularly during winter months, to cause aggravation to those most vulnerable to air pollution, such as asthmatics.

Groundwater quality may also be reduced by the leaching of metals such as aluminium from soils.

Control and Policy

Finland is committed to reducing sulphur emissions through the 1994 UNECE Protocol 'Further Reduction of Sulphur Emissions'. This protocol requires Finland to reduce sulphur emissions by 80% by year 2000 (on 1980 levels). Emissions of sulphur dioxide in Finland have fallen dramatically in the last 20 years and this commitment has been met. Finland is also a Party to the Gothenburg Protocol, designed to Abate Acidification, Eutrophication and Ground-level Ozone. Finalnd is committed to reducing 1990 emissions of sulphur dioxide by 75% by 2010 and nitrogen oxides by 50% over the same period.

UNITED KINGDOM

Key facts on United Kingdom

Population:
59.7 million (2000)

Size:
244 014 km²

Capital:
London (7.2 million population in Greater London)

Neighbours:
Ireland

Climate:
Marine West Coast, January (2-7°C), July (13-18°C)

Land use:
Agriculture 77%, forest 10%, urban 10%

Altitude:
0-800m above sea level

Air Quality:
Generally good in rural areas but ozone levels may be high during summer months. High emissions of acidic pollutants in large urban areas from industry and transport lead to potentially poor air quality.

Acid Deposition:
Amongst the highest acid deposition levels in Europe, particularly in eastern England.

Source: The Perry-Castañeda Library Map Collection, The General Libraries, The University of Texas at Austin, Austin, TX 78713-8916, USA

Acidic Pollutant Emissions

In the 1980s, the UK was described by Scandinavian countries as 'the dirty old man of Europe' due to high emissions of sulphur dioxide from industrial sources. Emissions of sulphur dioxide and oxides of nitrogen have since been reduced, resulting in emissions of 1.2 million tonnes of sulphur dioxide and 1.6 million tonnes of nitrogen oxides (as NO₂) in the UK during 1999. However, these amounts are still considerable compared to other European countries.

Most of the UK sulphur dioxide comes from power stations (65% in 1999) and other industries (22% in 1999) whilst the largest source of nitrogen oxides is road transport (44% in 1999) and power stations (21% in 1999). Total emissions of sulphurous and nitrogen oxides in 1990 and 1999 and their reductions over this time are shown in Table 3.5.

Table 3.5: Emissions of Acidifying Air Pollutants in UK

Reductions in UK sulphur dioxide have occurred largely through the reduction in use of coal by power stations and the installation of control technologies such as flue gas desulphurisation at Drax power station. Emissions of nitrogen oxides have also reduced from power stations as a result of increasing generation from Combined Cycle Gas Turbine and decreasing use of coal. Emissions from vehicles have slowly been falling since 1989 through increasing use of diesel fuel and the introduction of catalytic converters to all petrol engined cars sold since 1993. The reduction in nitrogen oxides in the UK has however slowed down due to increasing car ownership.

Acidic Pollutant Depositions

Air pollutants deposited on the UK originate not only from the UK but from other countries as well, as shown in Table 3.6.

Table 3.6: The Originating Countries of Sulphur and Nitrogen Deposition on UK

Total deposition of sulphur on UK during 1998 was around 0.33 million tonnes whereas the amount emitted in UK was more (1.19 million tonnes sulphur dioxide or 0.59 million tonnes sulphur, 1999). This highlights that the UK emits more sulphur pollution than is deposited in the UK. A significant proportion of sulphurous and nitrous pollutants are hence exported to other countries, mainly Germany, France, Norway, Sweden, the Netherlands and the Russian Federation in addition to the North Sea and Atlantic Ocean. The wind direction is the main factor affecting where UK pollutants are deposited.

The UK generally experiences high levels of acid deposition due to the large quantities of acidic pollutants emitted into the atmosphere each year.

Effects of Acid Deposition on Forests

In 1995, the United Nations Economic Commission for Europe (UNECE) Forest Survey revealed that 22% of UK trees were damaged (with 25% or more leaf or needle loss). Both coniferous and broadleaf trees showed the same degree of damage. Damage cannot be attributed to air pollution alone as many other factors such as climatic conditions, pests, age of tree, and exposure need to be considered. However, air pollution may cause an additional stress to trees and therefore may be a direct or indirect factor affecting tree health.

The commercial forest areas in the UK are mainly located in northern and western Britain where acid deposition is high due to higher levels of precipitation, mist and cloud. These areas of the UK are also particularly sensitive to acid deposition due to their granite-based bedrock offering low buffering capacity. Trees in these areas are more vulnerable to the effects of acid precipitation and air pollution

Effects of Acid Deposition on Water

Acidification studies in UK have shown that freshwater acidification is a serious problem in susceptible parts of the UK. These include central and south west Scotland, the Pennines, parts of Cumbria, central and North Wales and parts of Northern Ireland. Some lakes within these areas are acidified to the extent that they can no longer support many fish species.

Diatom analysis from lake sediments has shown that lake acidification has occurred in some UK freshwaters, with most rapid pH changes occurring since the 1950s. Freshwaters that have been intensively studied include Lyn Brianne in Wales and Loch Fleet in south west Scotland. The sensitivity of freshwaters in the UK has been studied and critical loads have been determined for areas of the UK. Critical loads are the amounts of acidic pollutants that an area can tolerate before damage occurs. Many areas of the UK already exceed such levels, although since the 1970s there is evidence that a recovery has taken place in response to significant reductions in emissions of sulphur dioxide.

Effects of Acid Deposition on Buildings

Acid deposition is known to accelerate normal weathering effects on buildings. Certain stone such as limestone, calcareous sandstone and marble have been shown to deteriorate faster through exposure to acid precipitation. Individual pollutants such as sulphur dioxide have effects on building materials, but pollutants can also act synergistically; nitrogen oxides and ozone may increase the effects of sulphur dioxide attack on certain materials.

On limestone, a black crust may form as pollutants react with the stone. This can accelerate damage as frost and other weather conditions cause this crust to blister and peel.

Many historic monuments and buildings are affected by air pollution in the UK and studies of cathedrals such as Lincoln and St. Paul's highlight that aspect and position are important factors in determining corrosion rates on historical buildings. The cost of damage to buildings is very difficult to estimate but includes costs of restoration to historic buildings which amounts to millions of pounds per year.

Effects of Acid Deposition on Health

The human health effects from acid deposition are not serious in the UK. Indirect effects may occur if ground or surface waters are contaminated by heavy metals leached from soils as a result of acidification. Health effects may occur as a result of the acidic pollutants in acid precipitation.

Back in the 1950s, the famous London smogs highlighted the serious nature of the effects of acidic pollutants on human health. 4,000 excess deaths were attributed to the effects of sulphur dioxide and particulate pollution during the December 1952 smog. Since then, smoke and sulphur dioxide levels have fallen considerably and such smogs are now history.

However, the UK does experience poor air quality episodes under certain climatic conditions which are sometimes classified by the UK Department of the Environment as "poor" air quality. Often such conditions occur during the summer months when photochemical reactions cause nitrogen oxides and hydrocarbons (mainly from traffic sources) to produce ozone. This can cause breathing difficulties amongst, for example, asthmatics. During different meteorological conditions such as temperature inversions, "poor" air quality may also occur when sulphurous and nitrous oxides build up in the atmosphere.

Control and Policy

The UK is committed to reducing sulphur emissions through the 1994 UNECE Protocol 'Further Reduction of Sulphur Emissions'. This protocol requires UK to reduce sulphur emissions by 50% by year 2000, 70% by 2005 and 80% by 2010 (all on 1980 levels). Emissions of sulphur dioxide in the UK have fallen dramatically in the last 20 years and this commitment has been met. The UK is also a Party to the Gothenburg Protocol, designed to Abate Acidification, Eutrophication and Ground-level Ozone. The UK is committed to reducing 1990 emissions of sulphur dioxide by 75% by 2010 and nitrogen oxides by 50% over the same period.

A 1988 Directive for European Union countries has also been introduced; it require all member countries to reduce emissions of sulphur dioxide and nitrogen oxides from Large Combustion Plants (over 50MW in size) by varying percentages. The UK is required to reduce sulphur dioxide by 60% by 2003 and nitrogen oxides by 30% by 1998 (on 1980 levels). The UK is well on course to exceed both of these targets, through new gas-fired power stations which produce smaller quantities of acidic pollutants than conventional coal fired stations, and flue gas desulphurisation equipment fitted to Drax and Ratcliffe on Soar power stations.

All petrol engined vehicles sold in EU countries since January 1993 have to be fitted with a catalytic converter. Catalytic converters reduce nitrogen oxide emissions from vehicles considerably compared with non-catalyst cars. However, there are still many non-catalyst cars in the UK and the increasing number of vehicles registered each year is likely to ensure that vehicular pollutants remain a major source of acidic pollution in the UK.

The introduction of the UK National Air Quality Strategy in March 1997 (and updated in 2000) is intended to achieve new air quality objectives throughout the UK by 2005, and hence improve air quality. The proposed standards and objectives of acid deposition pollutants under this new Strategy are shown in Table 3.7.

Table 3.7: The Proposed Standards and Objectives for Acid Deposition Pollutants
in the UK National Air Quality Strategy

The National Air Quality Strategy standards and objectives will require reductions in emissions from sources throughout the UK if the targets are to be met. This should form the basis for less acidic pollution in the UK over the coming years.

CANADA

Key facts on Canada

Population:
30.0 million (2001)

Size:
9 970 610 km²

Capital:
Ottawa

Neighbours:
United States of America, Alaska

Climate:
Cool temperate, polar in far north; January (-30 to -5°C), July (10-20°C)

Altitude:
0-3000+m above sea level

Air Quality:
Generally good in rural areas but ozone levels may be high during summer months. High emissions of acidic pollutants in large urban areas from industry and transport can lead to poor air quality.

Acid Deposition:
Eastern Canada is most sensitive to the effects of acid deposition because of its thin granitic soil. The sensitive area covers 43% of Canada, over 4 million km². Most of the emission sources are also located in the east of the country.

Source: The Perry-Castañeda Library Map Collection, The General Libraries, The University of Texas at Austin, Austin, TX 78713-8916, USA

Acidic Pollutant Emissions

The major sources of acidifying pollutants in Canada arise from human activities. The largest source of sulphur dioxide in Canada is from metal ore smelting and fossil fuel power generation whilst most of the nitrogen oxides arise from transport and industry. Emissions of sulphur dioxide have been falling over recent years, resulting in emissions of 2.7 million tonnes of sulphur dioxide in 1995, a 41% reduction from 1980. Emissions of nitrogen oxides remained fairly static at around 2 million tonnes between 1980 and 1995. Canadian emissions of sulphurous and nitrogen oxides are considerable but are less than the emissions from countries such as Germany, the UK, the Russian Federation and the United States of America. Emissions of sulphur dioxide from the neighbouring USA totalled approximately 16 million tonnes in 1995.

Most of the sulphur dioxide in Canada comes from metal ore smelting and other industrial sources (61% in 1995) and power generation (21% in 1995). The major source of nitrogen oxides in Canada is transport (59% in 1995). Total emissions of sulphurous and nitrogen oxides in 1980 and 1994 and their reductions over this time are shown in Table 3.8.

Table 3.8: Emissions of Acidifying Air Pollutants in Canada

Reductions in Canadian sulphur dioxide have occurred largely as a result of industrial process changes, installation of scrubbers, and fuel switching in the 1990s. Emission reductions of nitrogen oxides are being sought by the introduction of more stringent performance standards on exhaust emissions from new vehicles.

Acidic Pollutant Depositions

Fifty per cent of acid deposition in eastern Canada is estimated to originate from sources in the USA. Because of prevailing southerly winds during summer months, much of the pollution from the USA is exported to Canada. Some pollutants from Canada are transported to the US but on balance, Canada receives much more pollution than it exports. The import / export of pollutants across the border has therefore made acid rain a serious diplomatic issue between the US and Canada. The problem is compounded by the fact that the states in the US that are most heavily populated and have high air pollution emissions are located south of the sensitive eastern regions of Canada.

In a country as large as Canada, long range transport of pollutants means that pollutants emitted in one part of the country may be deposited hundreds or thousands of kilometres away in another part of Canada. With the continents of Europe and Asia being great distances away and separated from North America by the Pacific and Atlantic Oceans, acid pollutants from Canada are unlikely to be transported to countries other than neighbouring countries.

Eastern Canada generally experiences high levels of acid deposition due to the large quantities of acidic pollutants emitted into the atmosphere each year in the heavily populated areas (the southern border and the lakes) of Canada and from pollution imported from the US. Acid deposition is less serious in western Canada due to a less acid-sensitive environment and lower levels of acid deposition.

Effects of Acid Deposition on Forests

In 1995, the Acid Rain National Early Warning System indicated an absence of large scale decline in Canadian forests caused by atmospheric pollution. In certain areas however, a decline in health of one or more particular species was identified. A decline in the health of white birch (Betula papyrifera and B. cordifolia) in eastern Canada around the Bay of Fundy in New Brunswick and Nova Scotia was apparent as leaf browning and premature leaf fall. The area of concern experiences frequent acid fogs during summertime with pH 3.0 or less.

The Canadian sugar maple (Acer saccharum) has also been identified as having sustained reduction in growth with increasing levels of acid deposition. Maples on soils with low buffering capacity also show higher levels of dieback compared to those on well-buffered soils.

Effects of Acid Deposition on Water

Acidification studies in Canada have shown that freshwater acidification is a serious problem in Canada. Between 1986 and 1990 studies of 1 253 lakes in Quebec revealed that 19% had a pH level of less than 5.5, and 52% had a pH of less than 6.0. Acid deposition (mainly sulphuric acid) is thought to be largely responsible for the acidity of lakes in southwestern Quebec and natural organic acids the cause in northeastern Quebec.

Studies of lakes in Ontario, Quebec and the Atlantic Region between 1981 and 1994 have shown that lake acidity has improved in 33% of the 202 lakes studied, 56% remained stable and 11% have worsened. Lakes were noticeably less acidic in the Sudbury region of Ontario and this has been attributed to large reductions in sulphur dioxide emissions from Sudbury's nickel smelters. However, large reductions in sulphur dioxide in eastern Canada over recent years have not generally led to improvements in lake acidity in southern and eastern Canada. This is likely to be a result of the large quantities of pollutants being deposited which have originated in the United States.

Effects of Acid Deposition on Buildings

Acid deposition is known to accelerate normal weathering effects on buildings. The harsh climatic conditions in Canada cause degradation of materials because of the many freeze-thaw cycles that occur in winter and the high humidity in the summer. Acid deposition adds to this and effects can be seen for example on bronze statues in Montreal. The bronze becomes streaked with brown, black and blue-green surfaces which result from a combination of acid deposition, de-icing salts and corrosive dust.

Many historic monuments and buildings are slowly being eroded by acid rain, including the Parliament Buildings.

Effects of Acid Deposition on Health

There is concern in North America that human health is affected by acid deposition. The 1994 Canada - United States Air Quality Agreement have reported that long-term ambient exposures to acid aerosols have been linked to decrease in lung function in children. Acid aerosols are very tiny particles (less than 2.5 micrometres in size) which can enter the respiratory system and because of their size may filter through natural bodily defences. The basis of concern arises from a study of more than 10 000 children aged between 8 and 12 years in 24 North American cities. Most air pollution studies have been carried out on sensitive persons, such as asthmatics but this study identifies that acid aerosols have a detrimental effect on normal lung function.

Short-term exposure to poor air quality episodes may also cause breathing difficulties amongst for example asthmatics. These conditions may occur during summer months, particularly in cities where car pollution is the main source of nitrogen oxides.

Control and Policy

The long range transport of air pollutants is a problem which has long faced Canada. For many years Canada has been receiving much larger amounts of pollution from the United States than vice versa. After many research programmes were carried out during the 1980s, international agreements were set up between Canada and the US in 1991 for mutual reductions in sulphur dioxide and nitrogen oxide emissions. The history of control of acid rain in Canada and the US is outlined in Table 3.9.

Table 3.9: Canadian Acid Rain Control Chronology