Human and environmental health is jeopardized by exposure to sulfur dioxide (SO2), which is emitted into the atmosphere by numerous sources all across the globe. Monitoring levels of SO2, therefore, is vital to protect the population and the planet and to understand more about the detrimental impact of the compound so that this knowledge can influence regulations surrounding activities that emit dangerous gas.
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What Is Sulfur Dioxide and How Does It Enter the Environment?
SO2 is a dangerous air pollutant made from sulfur and oxygen. The compound also converts to sulfates in the atmosphere, a major source of fine particle pollution in the US. It enters the environment through many sources, most often as a result of burning non-renewable energy sources such as coal, oil, and diesel. Common activities that contribute to SO2 release include electricity generation (e.g. coal-fired power plants), metal processing, petroleum refining, diesel engines, and industrial boilers.
Each year in the US, human activity adds over 6.4 million tons of SO2 into the atmosphere. People who live or work close to major sources of SO2 emissions are those most at risk of the effects of exposure. However, once in the atmosphere, the compound converts into sulfate particles, which can travel in the air for hundreds of miles, impacting the population and landscape even at large distances from the initial source. This is troubling due to the known detrimental effects of SO2 on human health and the environment.
Sulfur Dioxide Exposure Linked to Mortality and Environmental Damage
Exposure to SO2, even at low concentrations, can irritate the skin as well as the mucous membranes of the eyes, nose, throat, and lungs as it enters the body via the airways. At high concentrations, exposure to SO2 can inflame and irritate the respiratory system, causing a myriad of symptoms, including pain when breathing deeply, breathing difficulties, throat irritation, and coughing. In the worst cases, SO2 can negatively impact lung function, worsen existing conditions such as asthma and heart disease, and increase the risk of respiratory tract infections.
According to a recent US Environmental Protection Agency (EPA) review, SO2 exposure increases the risk of hospital admissions or emergency room visits, particularly in children, the elderly, and those with asthma.
Research has revealed a non-linear relationship between exposure to SO2 and increased risk of all-cause and cause-specific mortality. It has also found evidence in favor of a positive relationship between SO2 exposure and lung cancer mortality.
In addition to the damage it can do to human health, SO2 has a detrimental impact on the environment. At high concentrations, SO2 can decrease the growth of trees and plants. Further to this, when it enters the atmosphere, SO2 combines with water and air to form sulfuric acid, the key ingredient of acid rain. The environment is put at a huge risk when it is exposed to acid rain, which causes deforestation, acidification of water sources and damage to aquatic life, and building corrosion.
Given the significant detrimental impact on human health and the environment, it is clear why monitoring sulfur dioxide is crucial. By monitoring dangerous gas levels, we can recognize when levels are dangerously high. We can also use this data to deepen our understanding of how gas impacts health and the environment; with this information, scientists can inform policymakers so that tighter restrictions can be placed on human activities that cause SO2 emissions.
How Is Sulfur Dioxide Monitored?
There are multiple methods available that are suitable for measuring SO2. The compound can be measured in air, water, food, and drink. Methods for measuring SO2 in the air include amperometric detection, calorimetry, conductimetry, flame photometric detection, ion chromatography, and turbidimetry. The most sensitive of these methods seems to be ion chromatography. SO2 can also be measured in stack gases by methods such as pulsed-fluorescence detection and titration. The National Institute for Occupational Safety and Health (NIOSH) recommends ion chromatography (method 6004) for measuring SO2 in ambient air.
In water, SO2 is reduced to sulfuric acid. To measure this, methods such as colorimetry, titration, and either acid distillation or alkali extraction ion exclusion chromatography with electrochemical detection are suitable. These methods can also measure SO2 in food and drink.
Throughout the US, air quality monitors are used to measure SO2 concentrations. This data is used by the Environmental Protection Agency (EPA), state, tribal, and local agencies to ensure that the concentrations of SO2 are kept to low levels to protect public and environmental health. It is vital that this work continues and that safe levels are revised regularly in light of any new evidence from scientific studies regarding the impact of SO2 exposure on human health or the environment.
References and Further Reading
Lee, W.J. et al. (2002) “Mortality from lung cancer in workers exposed to sulfur dioxide in the pulp and paper industry.,” Environmental Health Perspectives, 110(10), pp. 991–995. https://doi.org/10.1289/ehp.02110991.
Sulfur Dioxide Basics [Online]. US Environmental Protection Agency. Available at: https://www.epa.gov/so2-pollution/sulfur-dioxide-basics
What Is Sulfur Dioxide? [Online]. American Lung Association. Available at: https://www.lung.org/clean-air/outdoors/what-makes-air-unhealthy/sulfur-dioxide
Yorifuji, T. et al. (2018) “Acute exposure to sulfur dioxide and mortality: Historical data from Yokkaichi, Japan,” Archives of Environmental & Occupational Health, 74(5), pp. 271–278. https://doi.org/10.1080/19338244.2018.1434474.
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