Welcome to our latest dive into the realm of atmospheric chemistry with our “Molecule of the Month” series. This month, our spotlight falls on sulfur dioxide (SO₂), a ubiquitous yet often underestimated gas with profound implications for our environment and health. Join us as we unravel the complexities of SO₂, exploring its origins, effects, and the methods employed to measure its presence in our atmosphere.

Sulfur dioxide (O=S=O) is a colorless gas with a sharp, irritating odor. It plays a crucial role in atmospheric chemistry and has several important implications for the environment, climate and human health:

Environmental Impact: SO₂ is a major contributor to acid rain, devastatingly affecting ecosystems, water bodies, soil, and plant life. When SO₂ reacts with water vapor in the atmosphere, it forms sulfuric acid, leading to acidification of lakes and streams and damage to vegetation.

Importance to the Climate:  Sulfur dioxide also plays a significant role in climate regulation. It has both cooling and warming effects on the climate, depending on its concentration and interactions with other atmospheric components. SO₂ can form sulfate aerosols, which can reflect solar radiation and support the formation of clouds, leading to a cooling effect on the climate. However, sulfur dioxide emissions can also contribute to the greenhouse effect by absorbing and re-emitting infrared radiation, warming the atmosphere. Still, it is one of few atmospheric compounds with an estimated overall cooling impact.

Human Health: Exposure to sulfur dioxide can cause respiratory problems, aggravate existing lung diseases, and lead to cardiovascular issues. Short-term exposure to high levels of SO₂ can result in throat and eye irritation, while long-term exposure can cause more serious health problems, especially in vulnerable populations such as children, the elderly, and those with pre-existing health conditions.

Its sources can be devided into:

Anthropogenic Sources: The primary human-related sources of sulfur dioxide include the burning of fossil fuels (coal, oil, and gas) in power plants, industrial processes (such as smelting of metal ores), and vehicle emissions. These activities release significant amounts of SO₂ into the atmosphere, contributing to air pollution and environmental degradation.

Natural Sources: Natural sources of sulfur dioxide include volcanic eruptions and geothermal activities, which can release significant quantities of SO₂ into the atmosphere. While these sources can contribute to local and regional air quality issues, their impact is typically more episodic than continuous emissions from human activities.

As sulfur is usually removed during the refining process, the quality of a fuel defines the sulfur content and hence, if no catalysts are used, the sulfur content of the combustion emissions. As ship engines are more robust and heavy fuel combustion without extensive exhaust gas cleaning is cheaper, seafaring is a significant source of SO₂. The contribution of ships to the global emissions of SO₂ was estimated to be about 15%, while it is only 3% for CO₂. These high SO₂ emissions negatively impact air quality and ocean acidification. These emissions harm the environment and threaten the health of marine life, ecosystems, and human health.

The International Convention for the Prevention of Pollution from Ships (MARPOL) of the International Maritime Organization (IMO) sets limits on SO_x and NO_x emissions from ship exhausts. It has limited the SO_x emission in specified emission control areas (ECAs),, e.g. the North or Baltic Sea, to 0.10% and (outside of the ECAs) to 0.50%. To assure the implementation of these strict regulations, a direct monitoring method, measuring the SO₂/CO₂ ratio, has to be applied.

Accurate measurement of SO₂ concentrations is essential for assessing environmental impact and human exposure. Several techniques are employed for SO₂ detection:

UV Fluorescence Detection: Fluorescence detectors measure SO₂ concentrations based on the fluorescence emitted by SO₂ molecules when exposed to ultraviolet (UV) light. This method provides high sensitivity and specificity but can be affected by high humidity and the presence of other pollutants.

Electrochemical Sensors: Electrochemical sensors detect SO₂ by measuring the electrical current produced by the reaction of SO₂ with an electrolyte solution. These sensors are portable and cost-effective, making them suitable for both indoor and outdoor air quality monitoring. However, they may require frequent calibration and can be affected by temperature and humidity.

Non-Dispersive Infrared (NDIR) Spectroscopy: NDIR spectroscopy detects SO₂ by measuring the absorption of infrared radiation at specific wavelengths. This technique offers continuous, real-time monitoring and is widely used in air quality monitoring stations. However, it can be prone to interference from other gases and requires regular calibration.

 

 

Here, at MIRO Analytical, we use direct laser absorption spectroscopy (LAS) in the mid-infrared region to monitor SO₂ together with up to 9 gases. This technique offers highest sensitivity, selectivity, and real-time monitoring capabilities, making it ideal for ambient SO₂ measurements. As a robust multi-compound gas analyzer with high time resolution (up to 10Hz), MIRO´s MGA is ideal for ship exhaust plume chasing applications revealing the SO₂/CO₂ ratio as well as NOx concentrations. Its precision, wide dynamic range, and non-destructive nature contribute to its effectiveness in providing accurate and reliable data. Furthermore, LAS’ direct measurements of SO₂ are less susceptible to interference from other gases.

Conclusion:

Sulfur dioxide is a critical molecule with significant environmental, health, and climatic impacts. Understanding its sources, effects, and accurate measurement techniques is essential for effective air quality management and pollution control. By addressing SO₂ emissions, we can mitigate its adverse impact to the environment and human health, contributing to a cleaner, healthier, and more stable climate. Stay tuned for our next exploration into the fascinating world of gas molecules shaping our planet and lives! Remember, you cannot manage what you cannot measure!

 

 

About the author: Dr Jonas Bruckhuisen studied chemistry at the RWTH University in Aachen, Germany, before obtaining his PhD in gas phase spectroscopy and atmospheric science from the Université du Littoral Côte d’Opale in Dunkirk, France. He has been an application scientist at MIRO Analytical since 2023.