A Brief History of SO2
The oldest estimated sulphur dioxide emission data for most countries dates back to 1850, which was reconstructed based on fossil fuel production, imports, and industrial processing outputs. Industrialisation marked a significant transition point in the amount of sulphur dioxide emissions due to the large-scale burning of sulphur-containing fuels and industrial processing. Europe was the first one to show a rapid increase in sulphur pollution, followed by North America in the mid-19th century. As a result of increased energy demand of the industrialization, sulphur emission in Europe and North America did not stop rising until 1980 and 1970 respectively. In late 20th century and early 21st century, Europe, North America, and South America present a downward trend of sulphur emission. However, with the exception of Japan, industrialization in Asia, Latin America, and Africa began much later, and the sulphur emissions keep rising in those regions until present days.
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| fig.1 Regional emission of sulphur dioxide since 1850 to 2010 |
Health Impact
Some might be wondering that if sulphur dioxide also exists in the natural environment, for example, during a volcanic eruption, why should we concern about it? Isn't this nature? How could it affect our health and our environment? Well, unlike some other air pollutants, such as CO2, sulphur oxides merely stayed in the atmosphere, and only hold very low concentrations at the natural level. With industrial emission, exposures to this increased amount of sulphur dioxide in the atmosphere can harm the human respiratory system, and cause possible suffocation (like what happened in Meuse Valley).
According to the Canadian Centre for Occupational Health and Safety (CCOHS), the most toxic route of exposure is inhalation, which 'can cause severe irritation of the nose and throat' at low concentration and 'cause life-threatening accumulation of fluid in the lungs (pulmonary edema)' at high concentration. It only requires a single exposure to a high concentration of sulphur dioxide to cause long-term conditions such as asthma. Sulphur dioxide is also capable of causing health effect through skin contact and eye contact, which could lead to irritation or burn of the skin and the eyes and might result in permanent scarring and blindness. Besides its impact on the respiratory system, according to European Environment Agency, sulphur dioxide could even affect the central nervous system and cause headaches, general discomfort, and anxiety. However, there isn't solid evidence of any correlation between cancer and sulphur pollution.
Environmental Impact
Apart from sulphur dioxide's health impact, it also causes serious problems to the environment we live in. One of the most concerned environmental impacts of sulphur dioxide is acid rain, which forms when sulphur dioxide is transported by wind and air current, and finally, react with water to produce sulphur acid. The concept of acid rain was firstly suggested by Robert Angus Smith in the 19th century. The sulphur acid can be deposited through wet deposition, such as rain, snow, fog, or hail; and dry deposition, when the acidic particles and gases accumulate in water bodies, vegetation, buildings, etc or when the particles react in the atmosphere and form larger particles. Those acid depositions can cause serious effects on the ecosystem and the environment.
The ecological impacts of acid deposition are most common in aquatic environments, such as rivers, lakes, and oceans. When the acidic water flows through soils, it can leach aluminum from soil clay particles and then flow into water bodies. The more acidic the water is, the more aluminum it can release into the ecosystem.
Although some species of plants and animals are capable of tolerating acidic waters and a moderate amount of aluminum, others are acid-sensitive and will probably be harmed or even killed in low pH environment. The young of most species are usually more sensitive to environmental changes compare with the adults. When the pH level is as low as 5, most fish eggs would not be able to hatch, while some adult fish might die at lower pH levels, and some acidic lake does not even have fish. Even if some species of animal can tolerate the relatively high amount of acid and aluminum, the animal or plant it lives on may not. For instance, though frogs can survive a pH level around 4, the mayflies they feed on may would likely to be dead when the pH is under 5.5.
Besides animals, when acidic water leaches aluminum from the soil, it also removes minerals and nutrients that plants required for growing. At high elevations, acidic fog and clouds can strip nutrients from trees' leaves, and decline the trees' ability to absorb sunlight. As a result, the plants would be too weak to survive the freezing temperatures.
Treatment and Regulations
In order to remove sulphur dioxide from waste gases after fossil fuel combustion, the power stations treat sulphur dioxide with powdered limestone to form calcium sulfate. The sulfate can be further used to make plasterboard for lining interior walls.
Sulphur can also be removed from the fuels at the oil refinery state. In 2008, the International Maritime Organization (IMO) has been aiming for a lower global limit for the sulphur content of ships' fuel oil in 2020, which will be 0.05% m/m (mass by mass).
While the global cap now is 3.50% m/m.
Conclusion
Sulphur dioxide is one of the most threatening air pollutants nowadays. It mostly comes from fossil fuel combustion for industrial purposes and vehicles. To humans, it can be deadly, as it is able to affect our respiratory system and even cause suffocation. To the environment and the ecosystem, the acid rain result from gaseous sulphur dioxide can lead to a decline in plant and animal population and biodiversity.
So shall we call sulphur dioxide 'guilty' for all those problems it caused? If we look at the source of the air pollution, it's obvious that at the end of the day, we humans are the one to blame for the air pollution and the further problems it leads to. It is our responsibility to control and minimize the negative impacts. Protecting the environment and reducing air pollution is not distant and is not the factories' problem along. Everyone can participate in protecting the environment and ourselves from air pollution by small things in our daily life, for example, turning off the lights when leaving the room, using public transport instead of driving, reducing consumption to decrease demand on fuels and energy, etc.
According to the Canadian Centre for Occupational Health and Safety (CCOHS), the most toxic route of exposure is inhalation, which 'can cause severe irritation of the nose and throat' at low concentration and 'cause life-threatening accumulation of fluid in the lungs (pulmonary edema)' at high concentration. It only requires a single exposure to a high concentration of sulphur dioxide to cause long-term conditions such as asthma. Sulphur dioxide is also capable of causing health effect through skin contact and eye contact, which could lead to irritation or burn of the skin and the eyes and might result in permanent scarring and blindness. Besides its impact on the respiratory system, according to European Environment Agency, sulphur dioxide could even affect the central nervous system and cause headaches, general discomfort, and anxiety. However, there isn't solid evidence of any correlation between cancer and sulphur pollution.
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| Fig.2 Illustration of health effect due to sulphur dioxide and other air pollutants |
Environmental Impact
Apart from sulphur dioxide's health impact, it also causes serious problems to the environment we live in. One of the most concerned environmental impacts of sulphur dioxide is acid rain, which forms when sulphur dioxide is transported by wind and air current, and finally, react with water to produce sulphur acid. The concept of acid rain was firstly suggested by Robert Angus Smith in the 19th century. The sulphur acid can be deposited through wet deposition, such as rain, snow, fog, or hail; and dry deposition, when the acidic particles and gases accumulate in water bodies, vegetation, buildings, etc or when the particles react in the atmosphere and form larger particles. Those acid depositions can cause serious effects on the ecosystem and the environment.
 |
| fig.3 Pathway for acid rain in the environment |
The ecological impacts of acid deposition are most common in aquatic environments, such as rivers, lakes, and oceans. When the acidic water flows through soils, it can leach aluminum from soil clay particles and then flow into water bodies. The more acidic the water is, the more aluminum it can release into the ecosystem.
Although some species of plants and animals are capable of tolerating acidic waters and a moderate amount of aluminum, others are acid-sensitive and will probably be harmed or even killed in low pH environment. The young of most species are usually more sensitive to environmental changes compare with the adults. When the pH level is as low as 5, most fish eggs would not be able to hatch, while some adult fish might die at lower pH levels, and some acidic lake does not even have fish. Even if some species of animal can tolerate the relatively high amount of acid and aluminum, the animal or plant it lives on may not. For instance, though frogs can survive a pH level around 4, the mayflies they feed on may would likely to be dead when the pH is under 5.5.
 |
| fig.4 This figure illustrates the pH level at which key organisms may be lost as their environment becomes more acidic. Not all fish, shellfish, or the insects that they eat can tolerate the same amount of acid. |
Besides animals, when acidic water leaches aluminum from the soil, it also removes minerals and nutrients that plants required for growing. At high elevations, acidic fog and clouds can strip nutrients from trees' leaves, and decline the trees' ability to absorb sunlight. As a result, the plants would be too weak to survive the freezing temperatures.
Treatment and Regulations
In order to remove sulphur dioxide from waste gases after fossil fuel combustion, the power stations treat sulphur dioxide with powdered limestone to form calcium sulfate. The sulfate can be further used to make plasterboard for lining interior walls.
 |
| fig.5 Illustration of sulphur dioxide treatment in power stations |
Sulphur can also be removed from the fuels at the oil refinery state. In 2008, the International Maritime Organization (IMO) has been aiming for a lower global limit for the sulphur content of ships' fuel oil in 2020, which will be 0.05% m/m (mass by mass).
While the global cap now is 3.50% m/m.
Conclusion
Sulphur dioxide is one of the most threatening air pollutants nowadays. It mostly comes from fossil fuel combustion for industrial purposes and vehicles. To humans, it can be deadly, as it is able to affect our respiratory system and even cause suffocation. To the environment and the ecosystem, the acid rain result from gaseous sulphur dioxide can lead to a decline in plant and animal population and biodiversity.
So shall we call sulphur dioxide 'guilty' for all those problems it caused? If we look at the source of the air pollution, it's obvious that at the end of the day, we humans are the one to blame for the air pollution and the further problems it leads to. It is our responsibility to control and minimize the negative impacts. Protecting the environment and reducing air pollution is not distant and is not the factories' problem along. Everyone can participate in protecting the environment and ourselves from air pollution by small things in our daily life, for example, turning off the lights when leaving the room, using public transport instead of driving, reducing consumption to decrease demand on fuels and energy, etc.
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