Christian universalism

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Christian_universalism

Christian universalism is a school of Christian theology focused around the doctrine of universal reconciliation – the view that all human beings will ultimately be saved and restored to a right relationship with God. "Christian universalism" and "the belief or hope in the universal reconciliation through Christ" can be understood as synonyms. Opponents of this school, who hold that eternal damnation is the ultimate fate of some or most people, are sometimes called "infernalists."

The term Christian universalism was used in the Christian Intelligencer in the 1820s by Russell Streeter—a descendant of Adams Streeter who had founded one of the first Universalist Churches on September 14, 1785. Some Christian universalists claim that in Early Christianity (prior to the 6th century), this was the most common interpretation of Christianity.

As a formal Christian denomination, Christian universalism originated in the late 18th century with the Universalist Church of America. There is no single denomination uniting Christian universalists, but a few denominations teach some of the principles of Christian universalism or are open to them. Instead, their membership has been consolidated with the American Unitarian Association into the Unitarian Universalist Association in 1961.

Beliefs

In his Plain Guide to Universalism, the universalist Thomas Wittemore wrote, "The sentiment by which Universalists are distinguished, is this: that at last every individual of the human race shall become holy and happy. This does not comprise the whole of their faith, but, merely that feature of it which is peculiar to them and by which they are distinguished from the rest of the world."

The remaining central beliefs of Christian universalism are compatible with Christianity in general:

• God is the loving parent of all people (see Love of God).
• Jesus Christ reveals the nature and character of God and is the spiritual leader of humankind (see New Covenant).
• Humankind is created with an immortal soul which death does not end—or a mortal soul that shall be resurrected and/or preserved by God—and which God will not wholly destroy.
• Sin has negative consequences for the sinner either in this life or the afterlife.

In 1899 the Universalist General Convention, later called the Universalist Church of America, adopted the Five Principles: the belief in God, belief in Jesus Christ, the immortality of the human soul, that sinful actions have consequence, and universal reconciliation.

Views on hell

Christian Universalists disagree on whether or not hell exists. However, they do agree that if it does, the punishment there is corrective and remedial, and does not last forever.

Purgatorial hell and patristic universalism

Purgatorial universalism was the belief of some of the early church fathers, especially Greek-speaking ones such as Clement of Alexandria, Origen, and Gregory of Nyssa. It asserts that the unsaved will undergo hell, but that hell is remedial (neither everlasting nor purely retributive) according to key scriptures and that after purification or conversion all will enter heaven.

Fourth-century Christian theologian and Bishop Diodorus of Tarsus wrote: "For the wicked there are punishments, not perpetual, however, lest the immortality prepared for them should be a disadvantage, but they are to be purified for a brief period according to the amount of malice in their works. They shall therefore suffer punishment for a short space, but immortal blessedness having no end awaits them ... the penalties to be inflicted for their many and grave sins are very far surpassed by the magnitude of the mercy to be shown to them."

Ilaria Ramelli, a scholar of the early Patristic history writes, "In the minds of some, universal salvation is a heretical idea that was imported into Christianity from pagan philosophies by Origen" (c. 185–253/54). Ramelli argues that this view is mistaken and that Christian theologians were the first people to proclaim that all will be saved and that their reasons for doing so were rooted in their faith in Christ.

Eastern Orthodox theologian David Bentley Hart makes the case on the basis of the earliest Christian writings, theological tradition, scripture, and logic, that if God is the good creator of all, he is the savior of all, without fail.

Eternal hell in Christian history

Christian Universalists assert that the doctrine of eternal Hell was not a part of Christ's teachings nor even the early church, and that it was added in. The first clear mention of endless misery is to be found in a work from 155 to 165 AD by Tatian. According to theologian Edward Beecher, in the first four centuries there were six main theological schools and only one of them advocated the idea of eternal hell.

Origins of the idea of hell as eternal

Christian universalists point towards mistranslations of the Greek word αιών (aion – an epoch of time), as giving rise to the idea of eternal hell. Dr. Ken Vincent writes "When it (aion) was translated into Latin Vulgate, aion became aeternam which means 'eternal'." He also states that the first written record of the idea of an eternal hell comes from Tertullian, who wrote in Latin.

The second major source of the idea of hell as eternal was the 4th-century theologian Augustine. According to author Steve Gregg, it was Tertullian's writings, plus Augustine's views and writings on eternal hell, which "overwhelmed" the other views of a temporary hell. First Augustine's views of hell were accepted in the early Latin Church, Up until the Reformation Augustine's view of hell as eternal was not questioned.

Mistranslation of the Greek word aion

About the word aion as having connotations of "age" or "temporal", the 19th-century theologian Marvin Vincent wrote:

Aion, transliterated aeon, is a period of longer or shorter duration, having a beginning and an end, and complete in itself. Aristotle (peri ouranou, i. 9,15) says: "The period which includes the whole time of one's life is called the aeon of each one." Hence it often means the life of a man, as in Homer, where one's life (aion) is said to leave him or to consume away (Iliad v. 685; Odyssey v. 160). It is not, however, limited to human life; it signifies any period in the course of events, as the period or age before Christ; the period of the millennium; the mythological period before the beginnings of history.

The adjective aionios in like manner carries the idea of time. Neither the noun nor the adjective, in themselves, carry the sense of endless or everlasting. They may acquire that sense by their connotation, as, on the other hand, aidios, which means everlasting, has its meaning limited to a given point of time in Jude 6. Aionios means enduring through or pertaining to a period of time. Both the noun and the adjective are applied to limited periods.

Words which are habitually applied to things temporal or material cannot carry in themselves the sense of endlessness. Even when applied to God, we are not forced to render aionios everlasting. Of course the life of God is endless; but the question is whether, in describing God as aionios, it was intended to describe the duration of his being, or whether some different and larger idea was not contemplated.

Arguments against the idea of eternal hell

Author Thomas Talbott states that if one believes in the idea of eternal hell or that some souls will be destroyed, one must either let go of the idea that it is God's wish and desire to save all beings, or accept the idea that God wants to, but will not "successfully accomplish his will and satisfy his own desire in this matter".

Author David Burnfield defends the postmortem view that God continues to evangelize to people even after they die (1 Chronicles 16:34; Isaiah 9:2; Romans 8:35–39; Ephesians 4:8–9; 1 Peter 3:18–20; 4:6).

History

See also: History of Christian universalism

According to the New Schaff–Herzog Encyclopedia of Religious Knowledge (1912), over the first five hundred years of Christian history there are records of at least six theological schools: four of these schools were Universalist (one each in Alexandria, Antioch, Caesarea, and Edessa–Nisibis), one taught conditional immortality (in Ephesus), and the last taught eternal Hell (in Carthage or Rome). However, the Encyclopedia also notes that most contemporary scholars would take issue with classifying these early schools as Universalist.

An important figure in early American Christian Universalism was George de Benneville, a French Huguenot preacher and physician who was imprisoned for advocating Universalism and later emigrated to Pennsylvania where he continued preaching on the subject. De Benneville was noted for his friendly and respectful relationship with Native Americans and his pluralistic and multicultural view of spiritual truth which was well ahead of his time. One of his most significant accomplishments was helping to produce the Sauer Bible, the first German language Bible printed in America. In this Bible version, passages teaching universal reconciliation were marked in boldface.

Other significant early modern Christian Universalist leaders include Elhanan Winchester, a Baptist preacher who wrote several books promoting the universal salvation of all souls after a period in Purgatory, who founded the first Universalist church in Philadelphia, and founded a church that ministered to enslaved African Americans in South Carolina; Hosea Ballou, a Universalist preacher and writer in New England; and Hannah Whitall Smith, a writer and evangelist from a Quaker background who was active in the Holiness movement as well as the women's suffrage and temperance movements.

The Unity School of Christianity, founded in 1889 by Charles and Myrtle Fillmore, has taught some Universalist beliefs such as God's total goodness, the divine nature of human beings, and the rejection of the traditional Christian belief that God condemns people to Hell.

In the early 20th century, some Primitive Baptists in Appalachia started espousing Universalist ideas. By 1924, these churches branched off to form the Primitive Baptist Universalists. They are often known as "No Hellers" and believe that temporal punishment and separation from God during life is the only hell.

The logo of Universalist Church of America

The Universalist Church of America gradually declined in the early to mid 20th century and merged with the American Unitarian Association in 1961, creating the modern-day Unitarian Universalist Association, which does not officially subscribe to exclusively Christian theology. Christian Universalism largely passed into obscurity for the next few decades with the end of the Universalist Church as a separate denomination. However, the Unitarian Universalist Christian Fellowship remains as an organization for Christians from the Unitarian Universalist tradition and liberal Christians interested in Unitarianism and Universalism.

Some Christians from a Pentecostal background who were involved in the Latter Rain Movement of the 1940s and 1950s came to believe in the ideas of Christian Universalism on their own, separately from the Universalist Church tradition. They emphasized the teachings of universal reconciliation and theosis. These ideas were spread primarily through newsletters and traveling evangelists from the 1950s to 1980s, and were not typically identified by the term "Universalism". The only significant organization representing these beliefs that emerged within the Charismatic tradition was the Home Missions Church, a loosely organized network of ministers and house churches founded in 1944.

In 2007, the Christian Universalist Association was founded by thirteen ministers from diverse denominational backgrounds as an ecumenical organization promoting a revival of Christian universalism.

Universal reconciliation and pre-modern Christianity

Yale Professor of Philosophy Keith DeRose points out that in the Christian Scriptures there are verses which point to universal reconciliation and verses which point to destruction or eternal punishment for some. If looking only to scripture, he argues that Universalism is not only based in scripture, but has a stronger scriptural backing than the position of destruction or eternal damnation. Like early Christians, he points to Purgatorial Hell, a temporary place of cleansing of sin that will be necessary for some as a way to reconcile these seeming differences.

Modern types

There are three general types of Christian Universalism today – Evangelical Universalism, Charismatic Universalism, and Liberal Christian Universalism – which by themselves or in combination with one another describe the vast majority of currently existing and identifiable versions of Christian Universalist belief and practice.

Evangelical Universalism

The type of Christian Universalism that departs the least from orthodox or traditional Protestant Christian doctrine is Evangelical (Christian) Universalism, also called Biblical or Trinitarian Universalism. Evangelical Universalists hold to conservative positions on most theological or doctrinal issues except for the doctrine of hell, in which case they assert universal reconciliation instead of eternal torment. They tend to emphasize the substitutionary atonement of Jesus Christ for the sins of all humanity as the basis for their Universalism.

In 2006 a mainstream evangelical writer, revealed as Robin Parry in 2009, under the pseudonym of "Gregory MacDonald" (taken from the names, Gregory of Nyssa and George MacDonald) released a book, The Evangelical Universalist. In 2008 this inspired the creation of a forum, featuring "Gregory MacDonald" and Thomas Talbott, to discuss Evangelical Universalism and related topics. Evangelical Universalists derive a large part of their beliefs from Evangelicalism and Reformed theology. Many of them come from an Evangelical Christian background, but they may or may not identify with this movement and seek to remain with it.

Some Evangelical Universalists avoid using the word "Universalism" to describe their beliefs, perhaps because of the negative connotations of this word among conservative Christians. Alternative terms that are in use among Evangelical Universalists include the "Larger Hope" or "Blessed Hope" and the "Victorious Gospel".

Charismatic Universalism

Some Christians with a background in the Charismatic movement or Pentecostalism have developed a version of Universalism which could be called Charismatic (Christian) Universalism. Charismatic Universalists usually do not call their theology "Universalism" but commonly refer to their specific beliefs by the terms "Reconciliation" (shorthand for universal reconciliation, the doctrine of apocatastasis) and "Sonship" (shorthand for "Manifest Sonship" which is a variant of the doctrine of theosis). The term "Feast of Tabernacles" is used by some Charismatic Universalists as a term for their post-Pentecostal spiritual tradition, reflecting a symbolic interpretation of this Jewish festival as an entrance into a fuller knowledge and relationship with God and understanding of God's plan for humanity.

Charismatic Universalism is marked by its emphasis on theosis; the idea that the return of Christ is a body of perfected human beings who are the "Manifested Sons of God" instead of a literal return of the person of Jesus; the idea that these Sons will reign on the earth and transform all other human beings from sin to perfection during an age that is coming soon (a version of millennialism); and the absolute sovereignty of God, the nonexistence or severe limitation of human free will, and the inevitable triumph of God's plan of universal reconciliation.

Many Charismatic Universalists meet in house churches or do not belong to a church at all. Most of the evidence of Universalism existing as a school of thought within the Charismatic movement is found in a large number of internet-based ministries that are informally networked with one another.

Liberal Christian Universalism

Liberal Christian Universalists include some members of mainline Protestant denominations, some people influenced by the New Age and New Thought movements, some people in the emerging church movement, some Unitarian Universalists who continue to follow Jesus as their primary spiritual teacher, and some Christians from other religious backgrounds.

Liberal Christian Universalism emphasizes the all-inclusive love of God and tends to be more open to finding truth and value in non-Christian spiritual traditions compared to the attitude of other forms of Christian Universalism, while remaining generally Christ-centered. In contrast to Evangelical Universalism, Liberal Christian Universalism views the Bible as an imperfect human document containing divine revelations, is not necessarily Trinitarian, and often downplays or rejects blood atonement theology in its view of the crucifixion of Jesus. Some Liberal Christian Universalists believe in mystical philosophies such as panentheism and process theology, Gnostic or New Age ideas such as the preexistence and reincarnation of the soul, and New Thought ideas such as the law of attraction.

The Unitarian Universalist Christian Fellowship is an organization for Liberal Christian Universalists, especially those who belong to the Unitarian Universalist Association. The Unity Church is a liberal Christian denomination which teaches some Universalist beliefs.

The Liberal Catholic Church believes in Universal Salvation. Within its articles of faith it declares: "We believe that God is Love and Power and Truth and Light; that perfect justice rules the world; that all His sons shall one day reach His feet, however far they stray."

Hybrid types

Prior to his death in November 2023, former Pentecostal Bishop Carlton Pearson promoted his "Gospel of Inclusion" with his teachings and beliefs being a hybrid between Charismatic and Liberal Christian Universalism. A minister in the liberal Christian denomination of the United Church of Christ, Pearson continued to believe in ideas and practices of Pentecostal or Charismatic forms of Christianity. Pearson incorporated New Age and New Thought teachings into his message. Pearson was declared a heretic by his Christian Pentecostal and Charismatic peers in 2004.

Brian McLaren is a Christian leader in the emerging church movement who is sympathetic to the idea of Universalism but does not embrace it.

A number of ministers and evangelists connected with Restoration Nation conferences are Universalists who draw from both the Evangelical and Charismatic traditions. One notable example is Robert Rutherford, a minister from Georgia (USA) who was a finalist on The Learning Channel's 2006 reality TV series The Messengers. Another example is Dick King, an independent Charismatic Baptist pastor in North Little Rock, Arkansas, whose church left the Southern Baptist Convention in 2004.

Modern proponents

The conversion of Bishop Carlton Pearson to a form of Universalism and his subsequent excommunication by the Joint College of African-American Pentecostal Bishops in 2004 caused Christian Universalism to gain increased media attention because of Pearson's popularity and celebrity status.

Since 2007, the Christian Universalist Association has ordained more than 30 ministers in the United States and other countries who believe in Christian universalism.

Disagreements

There are many religious issues on which Christian Universalists disagree with each other, depending on their theological background and denominational tradition. Some examples include:

• Various views of atonement
• Whether non-Christians are saved through other means (inclusivism), or whether salvation occurs only after profession of belief in the Lordship of Jesus Christ (exclusivism).

Soil retrogression and degradation

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Soil_retrogression_and_degradation

Soil retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a stable soil. Retrogression is primarily due to soil erosion and corresponds to a phenomenon where succession reverts the land to its natural physical state. Degradation is an evolution, different from natural evolution, related to the local climate and vegetation. It is due to the replacement of primary plant communities (known as climax vegetation) by the secondary communities. This replacement modifies the humus composition and amount, and affects the formation of the soil. It is directly related to human activity. Soil degradation may also be viewed as any change or ecological disturbance to the soil perceived to be deleterious or undesirable.

According to the Center for Development Research at the University of Bonn and the International Food Policy Research Institute in Washington, the quality of 33% of pastureland, 25% of arable land and 23% of forests has deteriorated globally over the last 30 years. 3.2 billion people are dependent on this land.

General

At the beginning of soil formation, the bare rock outcrops are gradually colonized by pioneer species (lichens and mosses). They are succeeded by herbaceous vegetation, shrubs, and finally forest. In parallel, the first humus-bearing horizon is formed (the A horizon), followed by some mineral horizons (B horizons). Each successive stage is characterized by a certain association of soil/vegetation and environment, which defines an ecosystem.

Intensive tillage result on soil degradation

 

Willow hedge strengthened with fascines for the limitation of runoff, northern France

After a certain time of parallel evolution between the ground and the vegetation, a state of steady balance is reached. This stage of development is called climax by some ecologists and "natural potential" by others. Succession is the evolution towards climax. Regardless of its name, the equilibrium stage of primary succession is the highest natural form of development that the environmental factors are capable of producing.

The cycles of evolution of soils have very variable durations, between tens, hundreds, or thousands of years for quickly evolving soils (A horizon only) to more than a million years for slowly developing soils. The same soil may achieve several successive steady state conditions during its existence, as exhibited by the Pygmy forest sequence in Mendocino County, California. Soils naturally reach a state of high productivity, from which they naturally degrade as mineral nutrients are removed from the soil system. Thus older soils are more vulnerable to the effects of induced retrogression and degradation.

Ecological factors influencing soil formation

There are two types of ecological factors influencing the evolution of a soil (through alteration and humification). These two factors are extremely significant to explain the evolution of soils of short development.

• A first type of factor is the average climate of an area and the vegetation which is associated (biome).
• A second type of factor is more local, and is related to the original rock and local drainage. This type of factor explains appearance of specialized associations (ex peat bogs).

Biorhexistasy theory

Main article: biorhexistasy

The destruction of the vegetation implies the destruction of evoluted soils, or a regressive evolution. Cycles of succession-regression of soils follow one another within short intervals of time (human actions) or long intervals of time (climate variations).

The climate role in the deterioration of the rocks and the formation of soils lead to the formulation of the theory of the biorhexistasy.

• In wet climate, the conditions are favorable to the deterioration of the rocks (mostly chemically), the development of the vegetation and the formation of soils; this period favorable to life is called biostasy.
• In dry climate, the rocks exposed are mostly subjected to mechanical disintegration which produces coarse detrital materials: this is referred to as rhexistasy.

Perturbations of the balance of a soil

When the state of balance, characterized by the ecosystem climax is reached, it tends to be maintained stable in the course of time. The vegetation installed on the ground provides the humus and ensures the ascending circulation of the matters. It protects the ground from erosion by playing the role of barrier (for example, protection from water and wind). Plants can also reduce erosion by binding the particles of the ground to their roots.

A disturbance of climax will cause retrogression, but often, secondary succession will start to guide the evolution of the system after that disturbance. Secondary succession is much faster than primary because the soil is already formed, although deteriorated and needing restoration as well.

However, when a significant destruction of the vegetation takes place (of natural origin such as an avalanche or human origin), the disturbance undergone by the ecosystem is too important. In this latter case, erosion is responsible for the destruction of the upper horizons of the ground, and is at the origin of a phenomenon of reversion to pioneer conditions. The phenomenon is called retrogression and can be partial or total (in this case, nothing remains beside bare rock). For example, the clearing of an inclined ground, subjected to violent rains, can lead to the complete destruction of the soil. Man can deeply modify the evolution of the soils by direct and brutal action, such as clearing, abusive cuts, forest pasture, litters raking. The climax vegetation is gradually replaced and the soil modified (example: replacement of leafy tree forests by moors or pines plantations). Retrogression is often related to very old human practices.

Influence of human activity

Soil erosion is the main factor for soil degradation and is due to several mechanisms: water erosion, wind erosion, chemical degradation and physical degradation.

Erosion can be influenced by human activity. For example, roads which increase impermeable surfaces lead to streaming and ground loss. Improper agriculture practices can also accelerate soil erosion, including by way of:

• Overgrazing of animals
• Monoculture planting
• Row cropping
• Tilling or plowing
• Crop removal
• Land-use conversion

See also: soil contamination, soil salination, soil compaction, soil pollution, and soil health

Consequences of soil regression and degradation

Main article: land degradation

Here are a few of the consequences of soil regression and degradation:

• Yields impact: Recent increases in the human population have placed a great strain on the world's soil systems. More than 6 billion people are now using about 38% of the land area of the Earth to raise crops and livestock. Many soils suffer from various types of degradation, that can ultimately reduce their ability to produce food resources. This reduces the food security, which many countries facing soil degradation already do not have. Slight degradation refers to land where yield potential has been reduced by 10%, moderate degradation refers to a yield decrease of 10–50%. Severely degraded soils have lost more than 50% of their potential. Most severely degraded soils are located in developing countries. In Africa, yield reduction is 2–40%, with an average loss of 8.2% of the continent.^[8]
• Natural disasters: natural disasters such as mud flows, floods are responsible for the death of many living beings each year. This causes a cycle as floods can degrade soil, and soil degradation can cause floods.
• Deterioration of the water quality: the increase in the turbidity of water and the contribution of nitrogen and of phosphorus can result in eutrophication. Soils particles in surface waters are also accompanied by agricultural inputs and by some pollutants of industrial, urban and road origin (such as heavy metals). The run-off with pesticides and fertilizers make water quality dangerous. The ecological impact of agricultural inputs (such as weed killer) is known but difficult to evaluate because of the multiplicity of the products and their broad spectrum of action.
• Biological diversity: soil degradation may involve perturbation of microbial communities, disappearance of the climax vegetation and decrease in animal habitat, thus leading to a biodiversity loss and animal extinction.
• Economic loss: the estimated costs for land degradation are US$44 billion per year. Globally, the annual loss of 76 billion tons of soil costs the world about US$400 billion per year. In Canada, on-farm effects of land degradation were estimated to range from US$700 to US$915 million in 1984. The economic impact of land degradation is extremely severe in densely populated South Asia, and sub-Saharan Africa.

Soil enhancement, rebuilding, and regeneration

Problems of soil erosion can be fought, and certain practices can lead to soil enhancement and rebuilding. Even though simple, methods for reducing erosion are often not chosen because these practices outweigh the short-term benefits. Rebuilding is especially possible through the improvement of soil structure, addition of organic matter and limitation of runoff. However, these techniques will never totally succeed to restore a soil (and the fauna and flora associated to it) that took more than a 1000 years to build up. Soil regeneration is the reformation of degraded soil through biological, chemical, and or physical processes.

When productivity declined in the low-clay soils of northern Thailand, farmers initially responded by adding organic matter from termite mounds, but this was unsustainable in the long-term. Scientists experimented with adding bentonite, one of the smectite family of clays, to the soil. In field trials, conducted by scientists from the International Water Management Institute (IWMI) in cooperation with Khon Kaen University and local farmers, this had the effect of helping retain water and nutrients. Supplementing the farmer's usual practice with a single application of 200 kg bentonite per rai (6.26 rai = 1 hectare) resulted in an average yield increase of 73%. More work showed that applying bentonite to degraded sandy soils reduced the risk of crop failure during drought years.

In 2008, three years after the initial trials, IWMI scientists conducted a survey among 250 farmers in northeast Thailand, half who had applying bentonite to their fields and half who had not. The average output for those using the clay addition was 18% higher than for non-clay users. Using the clay had enabled some farmers to switch to growing vegetables, which need more fertile soil. This helped to increase their income. The researchers estimated that 200 farmers in northeast Thailand and 400 in Cambodia had adopted the use of clays, and that a further 20,000 farmers were introduced to the new technique.

Acid rain

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Acid_rain

Processes involved in acid deposition (only SO₂ and NO_x) play a significant role in acid rain

Acid clouds can grow on SO₂ emissions from refineries, as seen here in Curaçao.

Acid rain is rain or any other form of precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). Most water, including drinking water, has a neutral pH that exists between 6.5 and 8.5, but acid rain has a pH level lower than this and ranges from 4–5 on average. The more acidic the acid rain is, the lower its pH is. Acid rain can have harmful effects on plants, aquatic animals, and infrastructure. Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids.

Acid rain has been shown to have adverse impacts on forests, freshwaters, soils, microbes, insects and aquatic life-forms. In ecosystems, persistent acid rain reduces tree bark durability, leaving flora more susceptible to environmental stressors such as drought, heat/cold and pest infestation. Acid rain is also capable of detrimenting soil composition by stripping it of nutrients such as calcium and magnesium which play a role in plant growth and maintaining healthy soil. In terms of human infrastructure, acid rain also causes paint to peel, corrosion of steel structures such as bridges, and weathering of stone buildings and statues as well as having impacts on human health.

Some governments, including those in Europe and North America, have made efforts since the 1970s to reduce the release of sulfur dioxide and nitrogen oxide into the atmosphere through air pollution regulations. These efforts have had positive results due to the widespread research on acid rain starting in the 1960s and the publicized information on its harmful effects. The main source of sulfur and nitrogen compounds that result in acid rain are anthropogenic, but nitrogen oxides can also be produced naturally by lightning strikes and sulfur dioxide is produced by volcanic eruptions.

Definition

"Acid rain" is a popular term referring to the deposition of a mixture from wet (rain, snow, sleet, fog, cloudwater, and dew) and dry (acidifying particles and gases) acidic components. Distilled water, once carbon dioxide is removed, has a neutral pH of 7. Liquids with a pH less than 7 are acidic, and those with a pH greater than 7 are alkaline. "Clean" or unpolluted rain has an acidic pH, but usually no lower than 5.7, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid according to the following reaction:

H₂O (l) + CO₂ (g) ⇌ H₂CO₃ (aq)

Carbonic acid then can ionize in water forming low concentrations of carbonate and hydronium ions:

H₂O (l) + H₂CO₃ (aq) ⇌ HCO−3 (aq) + H₃O⁺ (aq)

Unpolluted rain can also contain other chemicals which affect its pH (acidity level). A common example is nitric acid produced by electric discharge in the atmosphere such as lightning. Acid deposition as an environmental issue (discussed later in the article) would include additional acids other than H₂CO₃.

Occasional pH readings in rain and fog water of well below 2.4 have been reported in industrialized areas.

The main sources of the SO₂ and NO_x pollution that causes acid rain are burning fossil fuels to generate electricity and power internal combustion vehicles, to refine oil, and in industrial manufacturing and other processes.

History

Acid rain was first systematically studied in Europe, in the 1960s, and in the United States and Canada, the following decade.

In Europe

The corrosive effect of polluted, acidic city air on limestone and marble was noted in the 17th century by John Evelyn, who remarked upon the poor condition of the Arundel marbles. Since the Industrial Revolution, emissions of sulfur dioxide and nitrogen oxides into the atmosphere have increased. In 1852, Robert Angus Smith was the first to show the relationship between acid rain and atmospheric pollution in Manchester, England. Smith coined the term "acid rain" in 1872.

In the late 1960s, scientists began widely observing and studying the phenomenon. At first, the main focus in this research lay on local effects of acid rain. Waldemar Christofer Brøgger was the first to acknowledge long-distance transportation of pollutants crossing borders from the United Kingdom to Norway – a problem systematically studied by Brynjulf Ottar in the 1970s. Ottar's work was strongly influenced by Swedish soil scientist Svante Odén, who had drawn widespread attention to Europe's acid rain problem in popular newspapers and wrote a landmark paper on the subject in 1968.

In the United States

Since 1998, Harvard University wraps some of the bronze and marble statues on its campus, such as this "Chinese stele", with waterproof covers every winter, in order to protect them from corrosion caused by acid rain and acid snow

The earliest report about acid rain in the United States came from chemical evidence gathered from Hubbard Brook Valley; public awareness of acid rain in the US increased in the 1970s after The New York Times reported on these findings.

In 1972, a group of scientists, including Gene Likens, discovered the rain that was deposited at White Mountains of New Hampshire was acidic. The pH of the sample was measured to be 4.03 at Hubbard Brook. The Hubbard Brook Ecosystem Study followed up with a series of research studies that analyzed the environmental effects of acid rain. The alumina from soils neutralized acid rain that mixed with stream water at Hubbard Brook. The result of this research indicated that the chemical reaction between acid rain and aluminium leads to an increasing rate of soil weathering. Experimental research examined the effects of increased acidity in streams on ecological species. In 1980, scientists modified the acidity of Norris Brook, New Hampshire, and observed the change in species' behaviors. There was a decrease in species diversity, an increase in community dominants, and a reduction in the food web complexity.

In 1980, the US Congress passed an Acid Deposition Act. This Act established an 18-year assessment and research program under the direction of the National Acidic Precipitation Assessment Program (NAPAP). NAPAP enlarged a network of monitoring sites to determine how acidic precipitation was, seeking to determine long-term trends, and established a network for dry deposition. Using a statistically based sampling design, NAPAP quantified the effects of acid rain on a regional basis by targeting research and surveys to identify and quantify the impact of acid precipitation on freshwater and terrestrial ecosystems. NAPAP also assessed the effects of acid rain on historical buildings, monuments, and building materials. It also funded extensive studies on atmospheric processes and potential control programs.

From the start, policy advocates from all sides attempted to influence NAPAP activities to support their particular policy advocacy efforts, or to disparage those of their opponents. For the US Government's scientific enterprise, a significant impact of NAPAP were lessons learned in the assessment process and in environmental research management to a relatively large group of scientists, program managers, and the public.

In 1981, the National Academy of Sciences was looking into research about the controversial issues regarding acid rain. President Ronald Reagan dismissed the issues of acid rain until his personal visit to Canada and confirmed that the Canadian border suffered from the drifting pollution from smokestacks originating in the US Midwest. Reagan honored the agreement to Canadian Prime Minister Pierre Trudeau's enforcement of anti-pollution regulation. In 1982, Reagan commissioned William Nierenberg to serve on the National Science Board. Nierenberg selected scientists including Gene Likens to serve on a panel to draft a report on acid rain. In 1983, the panel of scientists came up with a draft report, which concluded that acid rain is a real problem and solutions should be sought. White House Office of Science and Technology Policy reviewed the draft report and sent Fred Singer's suggestions of the report, which cast doubt on the cause of acid rain. The panelists revealed rejections against Singer's positions and submitted the report to Nierenberg in April. In May 1983, the House of Representatives voted against legislation that aimed to control sulfur emissions. There was a debate about whether Nierenberg delayed to release the report. Nierenberg himself denied the saying about his suppression of the report and stated that the report was withheld after the House's vote because it was not ready to be published.

In 1991, the US National Acid Precipitation Assessment Program (NAPAP) provided its first assessment of acid rain in the United States. It reported that 5% of New England Lakes were acidic, with sulfates being the most common problem. They noted that 2% of the lakes could no longer support Brook Trout, and 6% of the lakes were unsuitable for the survival of many species of minnow. Subsequent Reports to Congress have documented chemical changes in soil and freshwater ecosystems, nitrogen saturation, decreases in amounts of nutrients in soil, episodic acidification, regional haze, and damage to historical monuments.

Meanwhile, in 1990, the US Congress passed a series of amendments to the Clean Air Act. Title IV of these amendments established a cap and trade system designed to control emissions of sulfur dioxide and nitrogen oxides. Both these emissions proved to cause a significant problem on U.S. citizens and their access to healthy clean air. Title IV called for a total reduction of about 10 million tons of SO₂ emissions from power plants, close to a 50% reduction. It was implemented in two phases. Phase I began in 1995, and limited sulfur dioxide emissions from 110 of the largest power plants to a combined total of 8.7 million tons of sulfur dioxide. One power plant in New England (Merrimack) was in Phase I. Four other plants (Newington, Mount Tom, Brayton Point, and Salem Harbor) were added under other provisions of the program. Phase II began in 2000, and affects most of the power plants in the country.

During the 1990s, research continued. On March 10, 2005, the EPA issued the Clean Air Interstate Rule (CAIR). This rule provides states with a solution to the problem of power plant pollution that drifts from one state to another. CAIR will permanently cap emissions of SO₂ and NO_x in the eastern United States. When fully implemented, CAIR will reduce SO₂ emissions in 28 eastern states and the District of Columbia by over 70% and NO_x emissions by over 60% from 2003 levels.

Overall, the program's cap and trade program has been successful in achieving its goals. Since the 1990s, SO₂ emissions have dropped 40%, and according to the Pacific Research Institute, acid rain levels have dropped 65% since 1976. Conventional regulation was used in the European Union, which saw a decrease of over 70% in SO₂ emissions during the same time period.

In 2007, total SO₂ emissions were 8.9 million tons, achieving the program's long-term goal ahead of the 2010 statutory deadline.

In 2007 the EPA estimated that by 2010, the overall costs of complying with the program for businesses and consumers would be $1 billion to $2 billion a year, only one fourth of what was originally predicted. Forbes says: "In 2010, by which time the cap and trade system had been augmented by the George W. Bush administration's Clean Air Interstate Rule, SO₂ emissions had fallen to 5.1 million tons."

The term citizen science can be traced back as far as January 1989 to a campaign by the Audubon Society to measure acid rain. Scientist Muki Haklay cites in a policy report for the Wilson Center entitled 'Citizen Science and Policy: A European Perspective' a first use of the term 'citizen science' by R. Kerson in the magazine MIT Technology Review from January 1989. Quoting from the Wilson Center report: "The new form of engagement in science received the name "citizen science". The first recorded example of the use of the term is from 1989, describing how 225 volunteers across the US collected rain samples to assist the Audubon Society in an acid-rain awareness raising campaign. The volunteers collected samples, checked for acidity, and reported back to the organization. The information was then used to demonstrate the full extent of the phenomenon."

In Canada

Canadian Harold Harvey was among the first to research a "dead" lake. In 1971, he and R. J. Beamish published a report, "Acidification of the La Cloche Mountain Lakes", documenting the gradual deterioration of fish stocks in 60 lakes in Killarney Park in Ontario, which they had been studying systematically since 1966.

In the 1970s and 80s, acid rain was a major topic of research at the Experimental Lakes Area (ELA) in Northwestern Ontario, Canada. Researchers added sulfuric acid to whole lakes in controlled ecosystem experiments to simulate the effects of acid rain. Because its remote conditions allowed for whole-ecosystem experiments, research at the ELA showed that the effect of acid rain on fish populations started at concentrations much lower than those observed in laboratory experiments. In the context of a food web, fish populations crashed earlier than when acid rain had direct toxic effects to the fish because the acidity led to crashes in prey populations (e.g. mysids). As experimental acid inputs were reduced, fish populations and lake ecosystems recovered at least partially, although invertebrate populations have still not completely returned to the baseline conditions. This research showed both that acidification was linked to declining fish populations and that the effects could be reversed if sulfuric acid emissions decreased, and influenced policy in Canada and the United States.

In 1985, seven Canadian provinces (all except British Columbia, Alberta, and Saskatchewan) and the federal government signed the Eastern Canada Acid Rain Program. The provinces agreed to limit their combined sulfur dioxide emissions to 2.3 million tonnes by 1994. The Canada-US Air Quality Agreement was signed in 1991. In 1998, all federal, provincial, and territorial Ministers of Energy and Environment signed The Canada-Wide Acid Rain Strategy for Post-2000, which was designed to protect lakes that are more sensitive than those protected by earlier policies.

In India

Increased risk might be posed by the expected rise in total sulphur emissions from 4,400 kilotonnes (kt) in 1990 to 6,500 kt in 2000, 10,900 kt in 2010 and 18,500 in 2020.

Emissions of chemicals leading to acidification

The most important gas which leads to acidification is sulfur dioxide. Emissions of nitrogen oxides which are oxidized to form nitric acid are of increasing importance due to stricter controls on emissions of sulfur compounds. 70 Tg(S) per year in the form of SO₂ comes from fossil fuel combustion and industry, 2.8 Tg(S) from wildfires, and 7–8 Tg(S) per year from volcanoes.

Natural phenomena

The principal natural phenomena that contribute acid-producing gases to the atmosphere are emissions from volcanoes. Thus, for example, fumaroles from the Laguna Caliente crater of Poás Volcano create extremely high amounts of acid rain and fog, with acidity as high as a pH of 2, clearing an area of any vegetation and frequently causing irritation to the eyes and lungs of inhabitants in nearby settlements. Acid-producing gasses are also created by biological processes that occur on the land, in wetlands, and in the oceans. The major biological source of sulfur compounds is dimethyl sulfide.

Nitric acid in rainwater is an important source of fixed nitrogen for plant life, and is also produced by electrical activity in the atmosphere such as lightning.

Acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe.

Human activity

See also: Nitrogen cycle, Human impact on the nitrogen cycle, and sulfur cycle

The coal-fired Gavin Power Plant in Cheshire, Ohio

The principal cause of acid rain is sulfur and nitrogen compounds from human sources, such as electricity generation, animal agriculture, factories, and motor vehicles. These also include power plants, which use electric power generators that account for a quarter of nitrogen oxides and two-thirds of sulfur dioxide within the atmosphere. Industrial acid rain is a substantial problem in China and Russia and areas downwind from them. These areas all burn sulfur-containing coal to generate heat and electricity.

The problem of acid rain has not only increased with population and industrial growth, but has become more widespread. The use of tall smokestacks to reduce local pollution has contributed to the spread of acid rain by releasing gases into regional atmospheric circulation; dispersal from these taller stacks causes pollutants to be carried farther, causing widespread ecological damage. Often deposition occurs a considerable distance downwind of the emissions, with mountainous regions tending to receive the greatest deposition (because of their higher rainfall). An example of this effect is the low pH of rain which falls in Scandinavia. Regarding low pH and pH imbalances in correlation to acid rain, low levels, or those under the pH value of 7, are considered acidic. Acid rain falls at a pH value of roughly 4, making it harmful to consume for humans. When these low pH levels fall in specific regions, they not only affect the environment but also human health. With acidic pH levels in humans comes hair loss, low urinary pH, severe mineral imbalances, constipation, and many cases of chronic disorders like Fibromyalgia and Basal Carcinoma.

Chemical process

Combustion of fuels produces sulfur dioxide and nitric oxides. They are converted into sulfuric acid and nitric acid.

Gas phase chemistry

In the gas phase sulfur dioxide is oxidized by reaction with the hydroxyl radical via an intermolecular reaction:

SO₂ + OH· → HOSO₂·

which is followed by:

HOSO₂· + O₂ → HO₂· + SO₃

In the presence of water, sulfur trioxide (SO₃) is converted rapidly to sulfuric acid:

SO₃ (g) + H₂O (l) → H₂SO₄ (aq)

Nitrogen dioxide reacts with OH to form nitric acid:

This shows the process of the air pollution being released into the atmosphere and the areas that will be affected.

NO₂ + OH· → HNO₃

Chemistry in cloud droplets

When clouds are present, the loss rate of SO₂ is faster than can be explained by gas phase chemistry alone. This is due to reactions in the liquid water droplets.

Hydrolysis

Sulfur dioxide dissolves in water and then, like carbon dioxide, hydrolyses in a series of equilibrium reactions:

SO₂ (g) + H₂O ⇌ SO₂·H₂O

SO₂·H₂O ⇌ H⁺ + HSO₃⁻

HSO₃⁻ ⇌ H⁺ + SO₃²⁻

Oxidation

There are a large number of aqueous reactions that oxidize sulfur from S(IV) to S(VI), leading to the formation of sulfuric acid. The most important oxidation reactions are with ozone, hydrogen peroxide and oxygen (reactions with oxygen are catalyzed by iron and manganese in the cloud droplets).

Acid deposition

Wet deposition

Wet deposition of acids occurs when any form of precipitation (rain, snow, and so on) removes acids from the atmosphere and delivers it to the Earth's surface. This can result from the deposition of acids produced in the raindrops (see aqueous phase chemistry above) or by the precipitation removing the acids either in clouds or below clouds. Wet removal of both gases and aerosols are both of importance for wet deposition.

CAM plants are predominantly found in arid environments, where water availability is limited.

Dry deposition

Acid deposition also occurs via dry deposition in the absence of precipitation. This can be responsible for as much as 20 to 60% of total acid deposition. This occurs when particles and gases stick to the ground, plants or other surfaces.

Adverse effects

Acid rain has been shown to have adverse impacts on forests, freshwaters and soils, killing insect and aquatic life-forms as well as causing damage to buildings and having impacts on human health.

Surface waters and aquatic animals

Further information: Water pollution

Not all fish, shellfish, or the insects that they eat can tolerate the same amount of acid; for example, frogs can tolerate water that is more acidic (i.e., has a lower pH) than trout.

Both the lower pH and higher aluminium concentrations in surface water that occur as a result of acid rain can cause damage to fish and other aquatic animals. At pH lower than 5 most fish eggs will not hatch and lower pH can kill adult fish. As lakes and rivers become more acidic biodiversity is reduced. Acid rain has eliminated insect life and some fish species, including the brook trout in some lakes, streams, and creeks in geographically sensitive areas, such as the Adirondack Mountains of the United States.

However, the extent to which acid rain contributes directly or indirectly via runoff from the catchment to lake and river acidity (i.e., depending on characteristics of the surrounding watershed) is variable. The United States Environmental Protection Agency's (EPA) website states: "Of the lakes and streams surveyed, acid rain caused acidity in 75% of the acidic lakes and about 50% of the acidic streams". Lakes hosted by silicate basement rocks are more acidic than lakes within limestone or other basement rocks with a carbonate composition (i.e. marble) due to buffering effects by carbonate minerals, even with the same amount of acid rain.

Sulfur dioxide and nitrous oxide concentration has many implication on aquatic ecosystems, including acidity change, increased nitrogen and aluminum content, and altering biogeochemical processes. Typically, sulfur dioxide and nitrous oxide do not have direct physiological effects upon exposure; most effects are developed by accumulation and prolonged exposure of these gases in the environment, modifying soil and water chemistry.

Soils

Soil biology and chemistry can be seriously damaged by acid rain. Some microbes are unable to tolerate changes to low pH and are killed. The enzymes of these microbes are denatured (changed in shape so they no longer function) by the acid. The hydronium ions of acid rain also mobilize toxins, such as aluminium, and leach away essential nutrients and minerals such as magnesium.

2 H⁺ (aq) + Mg²⁺ (clay) ⇌ 2 H⁺ (clay) + Mg²⁺ (aq)

Soil chemistry can be dramatically changed when base cations, such as calcium and magnesium, are leached by acid rain, thereby affecting sensitive species, such as sugar maple (Acer saccharum).

Soil acidification

Diagram of nutrient leaching in soil with high levels of Soil acidity.

Impacts of acidic water and soil acidification on plants could be minor or in most cases major. Most minor cases which do not result in fatality of plant life can be attributed to the plants being less susceptible to acidic conditions and/or the acid rain being less potent. However, even in minor cases, the plant will eventually die due to the acidic water lowering the plant's natural pH. Acidic water enters the plant and causes important plant minerals to dissolve and get carried away; which ultimately causes the plant to die of lack of minerals for nutrition. In major cases, which are more extreme, the same process of damage occurs as in minor cases, which is removal of essential minerals, but at a much quicker rate. Likewise, acid rain that falls on soil and on plant leaves causes drying of the waxy leaf cuticle, which ultimately causes rapid water loss from the plant to the outside atmosphere and eventually results in death of the plant. Soil acidification can lead to a decline in soil microbes as a result of a change in pH, which would have an adverse effect on plants due to their dependence on soil microbes to access nutrients. To see if a plant is being affected by soil acidification, one can closely observe the plant leaves. If the leaves are green and look healthy, the soil pH is normal and acceptable for plant life. But if the plant leaves have yellowing between the veins on their leaves, that means the plant is suffering from acidification and is unhealthy. Moreover, a plant suffering from soil acidification cannot photosynthesize; the acid-water-induced process of drying out of the plant can destroy chloroplast organelles. Without being able to photosynthesize, a plant cannot create nutrients for its own survival or oxygen for the survival of aerobic organisms, which affects most species on Earth and ultimately ends the purpose of the plant's existence.  

Forests and other vegetation

Acid rain can have severe effects on vegetation. A forest in the Black Triangle in Europe.

Adverse effects may be indirectly related to acid rain, like the acid's effects on soil (see above) or high concentration of gaseous precursors to acid rain. High altitude forests are especially vulnerable as they are often surrounded by clouds and fog which are more acidic than rain.

Plants are capable of adapting to acid rain. On Jinyun Mountain, Chongqing, plant species were seen adapting to new environmental conditions. The affects on the species ranged from being beneficial to detrimental. With natural rainfall or mild acid rainfall, the biochemical and physiological characteristics of plant seedlings were enhanced. Once the pH increases reaches the threshold of 3.5, the acid rain can no longer be beneficial and begins to have negative affects.

Acid rain can negatively impact photosynthesis in plant leaves, when leaves are exposed to a lower pH, photosynthesis is impacted due to the decline in chlorophyll. Acid rain also has the ability to cause deformation to leaves at a cellular level, examples include; tissue scaring and changes to the stomatal, epidermis and mesophyll cells. Additional impacts of acid rain includes a decline in cuticle thickness present on the leaf surface. Because acid rain damages leaves, this directly impacts a plants ability to have a strong canopy cover, a decline in canopy cover can lead plants to be more vulnerable to diseases.

Dead or dying trees often appear in areas impacted by acid rain. Acid rain causes aluminum to leach from the soil, posing risks to both plant and animal life. Furthermore, it strips the soil of critical minerals and nutrients necessary for tree growth.

At higher altitudes, acidic fog and clouds can deplete nutrients from tree foliage, leading to discolored or dead leaves and needles. This depletion compromises the trees' ability to absorb sunlight, weakening them and diminishing their capacity to endure cold conditions.

Other plants can also be damaged by acid rain, but the effect on food crops is minimized by the application of lime and fertilizers to replace lost nutrients. In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but this tactic is largely unusable in the case of wilderness lands. When calcium is leached from the needles of red spruce, these trees become less cold tolerant and exhibit winter injury and even death. Acid rain may also affect crop productivity by necrosis or changes to soil nutrients, which ultimately prevent plants from reaching maturity.

Ocean acidification

Main article: Ocean acidification

Acid rain has a much less harmful effect on oceans on a global scale, but it creates an amplified impact in the shallower waters of coastal waters. Acid rain can cause the ocean's pH to fall, known as ocean acidification, making it more difficult for different coastal species to create their exoskeletons that they need to survive. These coastal species link together as part of the ocean's food chain, and without them being a source for other marine life to feed off of, more marine life will die. Coral's limestone skeleton is particularly sensitive to pH decreases, because the calcium carbonate, a core component of the limestone skeleton, dissolves in acidic (low pH) solutions.

In addition to acidification, excess nitrogen inputs from the atmosphere promote increased growth of phytoplankton and other marine plants, which, in turn, may cause more frequent harmful algal blooms and eutrophication (the creation of oxygen-depleted "dead zones") in some parts of the ocean.

Human health effects

Acid rain can negatively impact human health, especially when people breathe in particles released from acid rain. The effects of acid rain on human health are complex and may be seen in several ways, such as respiratory issues for long-term exposure and indirect exposure through contaminated food and water sources.

Nitrogen Dioxide Effects

Exposure to air pollutants associated with acid rain, such as nitrogen dioxide (NO2), may have a negative impact on respiratory health. Water-soluble nitrogen dioxide accumulates in the tiny airways, where it is transformed into nitric and nitrous acids. Pneumonia caused by nitric acids directly damages the epithelial cells lining the airways, resulting in pulmonary edema. Exposure to nitrogen dioxide also reduces the immune response by inhibiting the generation of inflammatory cytokines by alveolar macrophages in response to bacterial infection. In animal studies, the pollutant further reduces respiratory immunity by decreasing mucociliary clearance in the lower respiratory tract, which results in a reduced ability to remove respiratory infections.

Sulfur Trioxide Effects

The effects of sulfur trioxide and sulfuric acid are similar because they both produce sulfuric acid when they come into touch with the wet surfaces of your skin or respiratory system. The amount of SO3 breath through the mouth is larger than the amount of SO3 breath through the nose. When humans breathe in sulfur trioxide, small droplets of sulfuric acid will form inside the body and enter the respiratory tract to the lungs depending on the particle size. The effects of SO3 on the respiratory system lead to breathing difficulty in people who have asthma symptoms. Sulfur trioxide also causes very corrosive and irritation on the skin, eye, and gastrointestinal tracts when there is direct exposure to a specific concentration or long-term exposure. Consuming concentrated sulfuric acid has been known to cause mortality, burn the mouth and throat, erode a hole in the stomach, burns skin when it comes into contact with skin, and make your eyes weep if it gets into them.

Federal Government's recommendation

Nitrogen Dioxides

A 25 parts per million (ppm) maximum for nitric oxide in working air has been set by the Occupational Safety and Health Administration (OSHA) for an 8-hour workday and a 40-hour workweek. Additionally, OSHA has established a 5-ppm nitrogen dioxide exposure limit for 15 minutes in the workplace.

Sulfur Trioxide

The not-to-exceed limits in the air, water, soil, or food that are recommended by regulations are often based on levels that affect animals before being modified to assist in safeguarding people. Depending on whether they employ different animal studies, have different exposure lengths (e.g., an 8-hour workday versus a 24-hour day), or for other reasons, these not-to-exceed values can vary between federal bodies.

The amount of sulfur dioxide that can be emitted into the atmosphere is capped by the EPA. This reduces the quantity of sulfur dioxide in the air that turns into sulfur trioxide and sulfuric acid. Sulfuric acid concentrations in workroom air are restricted by OSHA to 1 mg/m³. Moreover, NIOSH advises a time-weighted average limit of 1 mg/m³.

When you are aware of NO2 and SO3 exposure, you should talk to your doctor and ask people who are around you, especially children.

Other adverse effects

Effect of acid rain on statues

Acid rain and weathering

Acid rain can damage buildings, historic monuments, and statues, especially those made of rocks, such as limestone and marble, that contain large amounts of calcium carbonate. Acids in the rain react with the calcium compounds in the stones to create gypsum, which then flakes off.

CaCO₃ (s) + H₂SO₄ (aq) ⇌ CaSO₄ (s) + CO₂ (g) + H₂O (l)

The effects of this are commonly seen on old gravestones, where acid rain can cause the inscriptions to become completely illegible. Acid rain also increases the corrosion rate of metals, in particular iron, steel, copper and bronze.

Affected areas

Places significantly impacted by acid rain around the globe include most of eastern Europe from Poland northward into Scandinavia, the eastern third of the United States, and southeastern Canada. Other affected areas include the southeastern coast of China and Taiwan.

Prevention methods

Technical solutions

Many coal-firing power stations use flue-gas desulfurization (FGD) to remove sulfur-containing gases from their stack gases. For a typical coal-fired power station, FGD will remove 95% or more of the SO₂ in the flue gases. An example of FGD is the wet scrubber which is commonly used. A wet scrubber is basically a reaction tower equipped with a fan that extracts hot smoke stack gases from a power plant into the tower. Lime or limestone in slurry form is also injected into the tower to mix with the stack gases and combine with the sulfur dioxide present. The calcium carbonate of the limestone produces pH-neutral calcium sulfate that is physically removed from the scrubber. That is, the scrubber turns sulfur pollution into industrial sulfates.

In some areas the sulfates are sold to chemical companies as gypsum when the purity of calcium sulfate is high. In others, they are placed in landfill. The effects of acid rain can last for generations, as the effects of pH level change can stimulate the continued leaching of undesirable chemicals into otherwise pristine water sources, killing off vulnerable insect and fish species and blocking efforts to restore native life.

Fluidized bed combustion also reduces the amount of sulfur emitted by power production.

Vehicle emissions control reduces emissions of nitrogen oxides from motor vehicles.

International treaties

Governmental action to combat the effects of acid rain

International treaties on the long-range transport of atmospheric pollutants have been agreed upon by western countries for some time now. Beginning in 1979, European countries convened in order to ratify general principles discussed during the UNECE Convention. The purpose was to combat Long-Range Transboundary Air Pollution. The 1985 Helsinki Protocol on the Reduction of Sulfur Emissions under the Convention on Long-Range Transboundary Air Pollution furthered the results of the convention. Results of the treaty have already come to fruition, as evidenced by an approximate 40 percent drop in particulate matter in North America. The effectiveness of the Convention in combatting acid rain has inspired further acts of international commitment to prevent the proliferation of particulate matter. Canada and the US signed the Air Quality Agreement in 1991. Most European countries and Canada signed the treaties. Activity of the Long-Range Transboundary Air Pollution Convention remained dormant after 1999, when 27 countries convened to further reduce the effects of acid rain. In 2000, foreign cooperation to prevent acid rain was sparked in Asia for the first time. Ten diplomats from countries ranging throughout the continent convened to discuss ways to prevent acid rain. Following these discussions, the Acid Deposition Monitoring Network in East Asia (EANET) was established in 2001 as an intergovernmental initiative to provide science-based inputs for decision makers and promote international cooperation on acid deposition in East Asia. In 2023, the EANET member countries include Cambodia, China, Indonesia, Japan, Lao PDR, Malaysia, Mongolia, Myanmar, the Philippines, Republic of Korea, Russia, Thailand and Vietnam.

Emissions trading

Main article: Emissions trading

See also: Acid Rain Program

In this regulatory scheme, every current polluting facility is given or may purchase on an open market an emissions allowance for each unit of a designated pollutant it emits. Operators can then install pollution control equipment, and sell portions of their emissions allowances they no longer need for their own operations, thereby recovering some of the capital cost of their investment in such equipment. The intention is to give operators economic incentives to install pollution controls.

The first emissions trading market was established in the United States by enactment of the Clean Air Act Amendments of 1990. The overall goal of the Acid Rain Program established by the Act is to achieve significant environmental and public health benefits through reductions in emissions of sulfur dioxide (SO₂) and nitrogen oxides (NO_x), the primary causes of acid rain. To achieve this goal at the lowest cost to society, the program employs both regulatory and market based approaches for controlling air pollution.