Introduction

Sulfur dioxide (SO₂) is a chemical compound with important industrial applications, but it is also recognized for its negative effects on human health and the environment. Its production is mainly generated in industrial processes such as the combustion of sulfur-containing fossil fuels and metal refining, especially in the energy and metallurgical industries. However, the proper management of this compound has become a problem for companies and environmental authorities due to its contributions to climate change, acid rain and air pollution.

In this context, sulfur dioxide chemistry involves not only its formation and utilization in various industrial applications, but also its management and emission reduction to mitigate its environmental impact. This article focuses on the sulfur dioxide production process, its implication in industry and current solutions for its control and minimization in urban and industrial environments.

Chemistry of sulfur dioxide (SO₂)

The sulfur produced as waste in refineries can be processed in desulfurization and sulfur recovery plants to 98%, when it is burned it is emitted into the atmosphere in the form of sulfur dioxide. It is a colorless gas with an unpleasant odor and irritant capacity that is also highly toxic and can cause strokes and lung cancer.

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Formed by sulfur (S) and oxygen (O), with the chemical formula SO₂, the structure of the sulfur dioxide molecule is symmetrical and forms an angle. The angle is due to the fact that SO₂ has a lone pair of electrons, i.e., electrons that do not form a bond with any atom but are free.

1 IMG 1 ING shutterstock 1060261433 Sulfur dioxide chemistry Fro resultado copia — Molecular structure of sulfur dioxide.

Sulfur dioxide: Characteristics

Sulfur dioxide (SO₂) is a colorless gas with a pungent, irritating odor, easily perceptible at concentrations of 0.3 to 1.4 parts per million (ppm) and clearly distinguishable at 3 ppm and above. Its density is approximately twice that of air, which causes it to tend to accumulate in low, poorly ventilated areas. Although it is not flammable or explosive, SO₂ is highly stable and exhibits high solubility in water. When it comes into contact with water, it transforms into sulfuric acid, a highly corrosive compound¹.

Chemically, sulfur dioxide is composed of one sulfur atom and two oxygen atoms. In the atmosphere, this gas oxidizes and gives rise to sulfates, which form part of PM10 particulate matter. In the presence of moisture, SO₂ generates acids in the form of aerosols, contributing significantly to the formation of secondary or fine particulate matter (PM2.5). This phenomenon is of particular concern, as these particles can be easily inhaled, reaching the lungs and circulatory system, posing a serious risk to human health.

One of the best known effects of sulfur dioxide is its role in the formation of acid rain. This occurs when SO₂ reacts with water in the atmosphere, giving rise to acids that precipitate with the rain, affecting ecosystems, soils, water bodies and built structures.

1 IMG 2 ING shutterstock 2357745173 Sulfur dioxide chemistry From production to en — Acid rain is the result of pollutants such as sulfur dioxide and nitrogen oxides.

Production and environmental effects

How is sulfur dioxide produced?

Emissions of SO₂ into the atmosphere come largely from human activities, especially from the combustion of petroleum products and the burning of coal in power plants, central heating and industrial processes. These sources release large quantities of this gas, contributing to air pollution and environmental deterioration.

In addition to anthropogenic sources, there are natural emissions of SO₂, mainly from volcanic activity. Volcanoes expel large quantities of this gas into the atmosphere during eruptions, influencing air quality locally and globally.

Sulfur dioxide is, therefore, an atmospheric pollutant of great impact, whose presence in the air not only affects the environment, but also represents a serious danger to human health, especially in people with respiratory or cardiovascular diseases.

Sulfur dioxide production in the industry

The generation of sulfur dioxide occurs by various industrial methods, the most common being:

Fossil fuel combustion: The burning of coal and oil is the main anthropogenic source of SO₂, accounting for about 50% of global emissions.
Sulfuric acid production: Obtained from the oxidation of SO₂ to sulfur trioxide (SO3), followed by its hydrolysis to sulfuric acid, this compound is essential in the manufacture of fertilizers, explosives and chemical products.
Pulp and paper industry: Used in the conversion of wood pulp into paper, releasing significant amounts of SO₂.
Waste incineration and metal refining: SO₂ is generated in the incineration of sulfur-containing materials and the refining of metals such as copper and lead.
Natural sources: Volcanic eruptions: Volcanoes emit large amounts of sulfur dioxide, contributing to the global atmospheric composition.

What are the environmental impacts of sulfur dioxide?

Sulfur dioxide is a corrosive gas that, upon reacting with atmospheric humidity, forms sulfurous acid (H₂SO₃) and sulfuric acid (H₂SO₄), the main causes of acid rain, alterations in aquatic ecosystems: it acidifies lakes and rivers, affecting biodiversity.

Environmental effects: Causes acid rain, degrades soils, damages vegetation and contaminates bodies of water, generates corrosion of infrastructure, affecting buildings and historical monuments.
Human health effects: Irritation of the respiratory system, causing asthma attacks and chronic lung diseases; prolonged exposure is linked to cardiovascular diseases.

Emission reduction and control technologies

To mitigate the impact of SO2, various technological and regulatory strategies have been implemented:

Sulfur reduction in fuels: Increasingly stringent regulations have driven the development of fuels with lower sulfur content, the transition to clean energy (hydrogen, electricity and synthetic fuels) reduces SO₂ emissions.
Capture and control technologies: Wet scrubbers: remove SO₂ from flue gases through chemical reactions, NOx and SOx adsorbents: capture more than 90% of these pollutants, and diesel particulate filters: optimize sulfur retention in internal combustion engines.
Emissions monitoring and control: Advanced technologies, such as Excimer UV Fluorescence (EUVF), enable accurate, real-time analysis of sulfur content in hydrocarbons and ATOM™ analyzers provide accurate measurements and comply with ASTM standards (D5453, D6667, D7551), ensuring environmental compliance.

International regulations on SO₂ emissions

Different countries have implemented strict regulations to control SO₂ emissions:

Industrial Emissions Directive (EU): Sets emission limits for industries and power plants.
EPA Regulation (USA): Regulates permitted levels of SO₂ in the atmosphere and promotes the use of capture technologies.
Geneva Convention on Air Pollution: International agreement to reduce the emission of polluting gases.
IMO 2020 Regulations (International Maritime Organization): Limits sulfur content in marine fuels to 0.5%.

Frequently asked questions

What are the main industrial methods for sulfur dioxide production?

The main methods include fossil fuel combustion, sulfuric acid production, paper manufacturing, metal refining and waste incineration.

What effects does sulfur dioxide have on human health and the environment?

SO₂ affects the respiratory system, worsening diseases such as asthma and chronic bronchitis. In the environment, it contributes to acid rain, soil degradation and damage to vegetation.

How does sulfur dioxide contribute to the formation of acid rain?

SO₂ oxidizes in the atmosphere, forming sulfuric acid. It combines with moisture and precipitates as acid rain, impacting ecosystems and structures.

What international regulations control sulfur dioxide emissions?

Among the main regulations are the EU Industrial Emissions Directive, U.S. EPA regulations, the Geneva Convention and the IMO 2020 regulation for marine fuels.

With the advancement of monitoring technologies and environmental regulations, the reduction of sulfur dioxide in the atmosphere is a key objective for industrial and environmental sustainability.

Conclusions

In conclusion, sulfur dioxide is a compound of great relevance in both industry and environmental science. While its production remains essential in sectors such as power generation and mining, the adverse effects on health and the environment are undeniable, which has led to the urgent need to implement control and reduction measures.

Understanding the chemistry of sulfur dioxide allows the development of more efficient technologies for its capture and treatment, promoting a transition towards more sustainable industrial processes. Thus, although industry continues to use this compound, it is essential to continue innovating strategies to minimize its impact, ensuring a balance between industrial development and environmental protection.