ACID RAIN The science of acidic deposition ydlbsna Acid Rain - The Scii^nce of Acidic De.posilion Acid Rain, The Science of Acidic Deposition is published by Alberta Environment. This material is under Crown Copyright and may be freely copied for educational use provided the source is acknowledged. For additional copies, contact: Information Centre - A lberta Environment Main Floor, Great West Life Building 9920- 108 Street Edmonton, Alberta Canada T5K 2M4 Phone: (780) 944-03 1 3 (Monday to Friday - 8: 1 5 to 1 6:30 Mountain Time) Fax: (780) 427-4407 Email: [email protected] Web: www.gov.ab.ca/env/ Updated March 2001 *Note: this is a draft version and subject to revision 2 Acid Ruin - ■ T he Scicfice of Acidic Deposilion TABLE OF CONTENTS CHAPTER ONE 5 ACID RAIN: THE SCIENCE OF ACIDIC DEPOSITION 5 How do we know the strength of a n acid? 6 What is acidic deposition? 7 Sources of acidic deposition 7 Transportation and movement of a irborne acids 9 Buffering capacity 10 Aquatic effects of a cidic deposition 10 Tolerance 11 Leaching of m etals from soils and sediments 12 Sources and Solutions 13 Coal-Fired Electrical Plants 13 Non-Ferrous Smelting Industries 14 Transportation 14 Sour Gas Plants 15 Personal Action 15 CHAPTER TWO 16 Sources Of Acidic Deposition 16 Activity 1 - W hat are the major sources of sulphur dioxide in Alberta? 19 The chemistry of s ulphur dioxide 21 Activity 2 - W hat are the major sources of nitrogen oxide compounds in Alberta? 22 The chemistry of n itrogen oxide compounds 23 Activity 3 - W hat amounts of sulphur dioxide and nitrogen oxide compounds are produced in different regions of Alberta? 25 Activity 4 - W hat amounts of sulphur dioxide and nitrogen oxide compounds are produced in different parts of Canada? 27 Monitoring Changes in the Environment 28 Activity 5 - H ow is the pH of an acid determined by titration? 28 CHAPTER THREE 33 Buffering Capacity 33 Demonstration 1- What is an indicator? 33 Demonstration 2 - W hat is a buffer? .....35 Activity 6 - D oes soil contain a natural buffer system? 36 Activity 7 - H ow do soils vary in the response to changes in pH? 37 Activity 8 - D oes a lake or river water contain a natural buffer system? 41 Activity 9 - W hat is the relationship between locations of acidic deposition, sensitivity of soil, and sensitivity of water in Alberta? 43 CHAPTER FOUR 47 The Effects Of Acidic Deposition 47 Problem 1 - W hat is the effect of simulated acid rain on plant growth? 47 Problem 2 - W hat is the effect of pH on the availability of soil nutrients? 52 Problem 3 - D o all plants require the same soil pH? 53 Problem 4 - H ow does a change in pH affect a natural aquatic community? 55 CHAPTER FIVE 61 Solutions To Acidic Deposition 61 Decrease the pollutants in the fuel. 62 Decrease pollutants during combustion 62 Remove pollutants from the exhaust and flue gases 63 Activity 10 - E valuation of Competing Technology 68 Deciding Which Technology to Use 71 Conservation of e nergy 73 Non-combustion energy sources 73 3 Acid Rain - The Science of Acidic Dcposilion CHAPTER SIX 76 Acidic Deposition - A Socio-Economic Perspective 76 Notes to the Teacher 76 Inside Acid Rain... A Socio-Economic Perspective 77 Acid Rain: The Canadian Perspective 78 Acid rain: A Brief Canadian Case History 79 Chronology of events: 79 Canada-United States Relations 81 Economics of A cidic Deposition 84 The Cost of I mplementing Pollution Controls 85 The Costs Associated with NOT Implementing Pollution Control: 86 Human Health and Acidic Deposition , 86 Sustainable Development 87 The role of t he individual 88 The role of i ndustry: 88 The role of g overnment: 89 Summary 89 Suggested Socio-Economic Activities 90 Activity 1 1 - V ideo Investigation 90 Activity 12 - Conducting a Poll 92 Activity 1 3 - E ssay Writing 93 Activity 14 - D esign a Chronological Map of the Acidic Deposition Issue 94 Activity 1 5 - A cidic Deposition in the Headlines 94 Activity 16 - F act or Fiction 95 4 .Icid Rain ■ The Science of A cidic Deposiiion CHAPTER ONE ACID RAIN: The science of acidic deposition Imagine being on a tour of Canadian regions affected by acidic deposition. Your first stop is a small community north of Sudbury, Ontario. The land is barren, rocky and supports only a sparse amount of stunted vegetation. There appears to be little sign of wildlife in the area. Your torn- guide explains that this area has been exposed to varying degrees of acidic deposition for close to one hundred years. Your next stop seems to contradict your first impression of the environment's response to acidic deposition. You are standing on a hillside overlooking a beautiful lake with crystal clear water. The scene is postcard perfect, yet in this case beauty can be dangerously deceiving. "The lake", your tour guide informs you, "is a victim of acidic deposition. The water is clear only because the lake is virtually dead. Only a few very tolerant species now inhabit this aquatic environment." These scenes are the result of an environment exposed to acidic deposition in amounts greater than can be tolerated. The long-term consequences of acidic deposition reach into the political, economic and environmental realms of our society. Acidic deposition is a serious concern that has varying degrees of regional and global impact. The extent of the impact is dependent upon a variety of factors, including: ■ concentration and length of exposure ■ source and type of acidic deposition ■ climate ■ geological characteristics Unlike many environmental issues that demand immediate attention, acidic deposition is a silent, gradual threat that often goes unnoticed until the damage has been done. It is estimated in Eastern Canada alone, 150,000 lakes are gradually succumbing to the effects of increasing acidity. Unless these lakes are monitored, there is often no way of realizing the actual impact until the damage has become extreme. In North America, public perception of the issue has been shaped to a large extent by accounts of the situation in the eastern half of the continent. Media accounts, environmental interest groups, scientists and government representatives have contributed to this perception. As Albertans, we need to be aware of the global and national concerns as well as the more regional effects that deal with Alberta's situation. 5 Aci'J Rain - The Science of Acidic Deposition How do we know the strength of an acid? The strength of an acid or base is measured using an instrument called a pH meter. pH describes how acidic or alkaline (basic) a substance or solution is. The pH scale ranges from 0 which is very acidic to 14 which is very basic. A pH value of 7 is neutral and is characteristic of distilled water. An acid that has a pH of 4.5 on this scale would be ten times more acidic that an acid that has a pH of 5.5. A change of 1 pH unit represents a ten-fold change in concentration. The following chart illustrates the pH values of a variety of common substances. ALKALINE NEUTRAL ACIDIC pH above 7 = alkalinity pH below 7 = acidity 14 13 12 11 10 9 8 7 6 5 4 3 2 1 , from Caradtan GeoQraphic Nov 19SE Figure 1 : p H values of c ommon substances 6 Acici Rain - - 7 7?;:; Science of A cidic Dcposiiion What is acidic deposition? Often, the term acid rain is used when describing the effects of acidification on lakes and soils. The effect can be the result of both wet and dry acidic pollutants that eventually settle out of the atmosphere. These wet and dry pollutants are collectively referred to as acidic deposition. Acid rain, snow, hail, sleet and fog are formed when dry acidic particles combine with moisture in the air to form mild acids. These fall to earth as wet acidic deposition. Normal rain has a pH value of 5.6. This slight acidity is the result of the rain combining with carbon dioxide to form a mild carbonic acid solution. Any precipitation that has a pH value lower than 5.6 is defined as wet acidic deposition. If the acidic pollutants in the atmosphere do not combine with moisture, they often chemically attach themselves to dust particles in the air and settle out as dry acidic deposition. These dry particles — — will form a mild acid once they are exposed to moisture on the ground. The total effect of acidic deposition on an area is related to the amount of wet and dry acidic deposition an area is exposed to. Sources of acidic deposition The compounds most commonly responsible for acid deposition are produced largely fi-om human-related activities. These compounds are sulphur dioxide (SO2) and nitrogen oxides (NOx). Sulphur dioxide is a by-product of several large-scale industrial processes including the burning of fossil fiiels for power, heating, and transportation. Sulphur dioxide can combine with moisture in the air to form weak sulphuric acid (H2SO4), or it c an chemically combine with dust and other airborne particles and settle out as dry acidic deposition. Coal fired power generators are largely responsible for SO2 emissions because of the sulphur content of the coal that is being burned. During this process, the sulphur is released and combines with oxygen during combustion to form sulphur dioxide. Non-ferrous smelting industries are also responsible for large-scale production of SO2. The ore is heated to extremely high temperatures in order to separate the nickel, copper, lead or zinc. This causes the sulphur within the ore to be released, forming SO2 as it c ombines with oxygen. 7 Acid Rain - The Science of A cidic Deposiiion In Alberta, the main source of acidic deposition is from sour gas refineries that release SO2 during the refining process. There are two types of natural gas in Alberta. Sweet natural gas is the most preferred because it does not contain hydrogen sulphide (H2S), a poisonous gas that has a distinct rotten egg odour. Sour gas, on the other hand, has a high H2S content and must be refined prior to being used. In Alberta, approximately one quarter of all natural gas reservoirs contain sour gas. The dry and windy conditions, characteristic of southern Alberta where the majority of natural gas pockets are located, contribute to an increase in widely dispersed dry acidic deposition. Other sources of SO2 in Alberta include the processes related to refining oil sands into crude oil. SO2 can also be produced naturally through the decomposition of organic material and events such as volcanoes and fires. These events contribute to global concentration of airborne SO2. Human-created SO2, however, is responsible for approximately 90% of the total amount of airborne sulphur dioxide in North America. Nitrogen oxides include nitrogen dioxide (NO2) and nitrogen oxide (NO). These nitrogen compounds are the second major contributor to acidic deposition. Nitrogen oxides are formed when nitrogen present in fossil fuel and in the atmosphere combines with oxygen under high temperature conditions. NOx pollution results largely from our North American dependence on the automobile for transportation. Approximately 70% of all NOx in the atmosphere is produced by human-related activities. The addition of fertilizer to nutrient poor soils can also produce NOx. Ammonia (NH4) produced by animals and from the manufacturing of fertilizers can also contribute to NOx in the atmosphere. Through a series of chemical reactions, the nitrogen oxides are converted to nitrates which can be converted to weak nitric acid (HNO3) when exposed to moisture in the air or on the ground. 8 Acid Rain - The Science of Acidic Dcposinon Presently in Alberta, the single largest source of NOx is the transportation sector, which accounts for almost 40% of the total emissions. The largest potential for reduction is within the natural gas and transportation sectors. NOx emissions are expected to increase by 60-80% from 1980 levels by the year 2000. By using improved technology, however, it i s expected that there will be little change in actual emissions entering the atmosphere compared to 1980 levels. Transportation and movement of airborne acids Airborne acidic pollutants do not necessarily contaminate the regions where they are produced. Vivid examples illustrating this situation include the controversial American-produced acidic pollutants coming from outdated coal-fired electrical plants. These pollutants eventually cause an increase in aquatic and soil acidity in Eastern Canada. Approximately 50% of eastern Canada's acidic deposition pollution has been linked to pollutants produced south of the border. However, it has been difficult to negotiate a solution with any credibility when Canadian-based industries are also responsible for producing considerable SO2 and NOx emissions; some of which ultimately end up as acidic deposition in the United States. To ftirther illustrate the capacity of acidic pollutants to travel large distances, one only has to take a historical look at the INCO non-ferrous smelting plant located in Sudbury, Ontario. INCO has been operating for over 75 years. In the early years of non-ferrous smelting, the ore was heated to great temperatures in open air pits. The resulting acidic emissions eventually increased the water and soil acidity of the surrounding area to the point where habitats were destroyed and entire ecosystems disappeared. The "denuded moonscape" appearance of the landscape near Sudbury is the direct resuU of over acidification. In response to this, a large (381 meter) superstack was erected to disperse the pollutants and to decrease the concentration of the acidic deposition in the surrounding region. This solution, although beneficial to areas closer to the source, creates an increase in acidic deposition in areas fiirther removed. Once the sulphur dioxide and nitrogen dioxide compounds are produced, the length of time they stay airborne and the distance they travel will determine how far they are removed from the actual source. Climatic conditions play a major role in determining the destination of acidic pollutants. Sulphates and nitrates, the precursors to acidic deposition, can generally last about four days as airborne particles. The movement of the particles is determined by wind speed and direction. Alberta does not currently generate nor receive significant quantities of acid- forming emissions from outside of provincial or national boundaries. Any emissions that are generated within Alberta usually move north toward the Northwest Territories or eastward into Saskatchewan. As Alberta oil sands development continues to increase, there is a potential for fiiture problems to exist as acidic pollutants move into more vulnerable areas in northeastern Alberta, the Northwest Territories, and northern Saskatchewan. Within Alberta, dry deposition from short-range, locally produced pollutants, are the major contributors of acidic deposition. 9 Acid Rain The Science of A cidic Deposit ion Buffering capacity The acidic deposition situation in eastern Canada is distinct from Alberta in several ways. The first distinction is related to the volume and type of acidic deposition that falls on these regions. The second is related to the characteristics of the land on which these pollutants fall. Eastern Canada is very vulnerable to the accumulative effects of acidic deposition because the soils and lakes are not capable of neutralizing the acid. Li Alberta, most regions have alkaline soils that can absorb acidic deposition without an accompanying decrease in pH values. This capacity for the soil to act as a buffer to neutralize the acidity is important in combating the effects of acidic deposition. Eastern Canada, because of its large areas of granite and exposed bedrock, has very little natural buffering capacity and is therefore susceptible to the effects of acidic deposition. The aquatic systems of the region have similar buffering characteristics as the soils because the sediment in the lakebeds is usually of the same composition as the surrounding land. Alberta does have some potentially vulnerable areas in the northeastern areas of the province where part of the Canadian Shield is exposed. The lakes and soils in this region do not have good buffering capacity. Dust particles in the air can also neutraUze acidic pollutants. Soils, particularly in southern Alberta, are naturally high in alkalinity. Wind movement causes some of this dust to become suspended in the atmosphere. These particles can attach themselves to acidic pollutants or they can combine with tiny water droplets to form rain. This rain, can, in some instances, have a pH greater than 5.6. Prolonged exposure can cause a region to lose its buffering capacity. When this happens, the pH begins to decrease and the environment begins to demonstrate the effects of increased acidity. For long periods of time, there may be no evidence of acidification. Once the balance point has been reached, it t akes very little time for a region to dramatically drop in pH. At this point, the environmental effects become evident. Aquatic effects of acidic deposition The biological, physical, and chemical characteristics of an aquatic ecosystem determine how sensitive an area is to acidic deposition. In a lake's ecosystem, acidic pollutants are deposited 10