Sulfur dioxide (SO2) is a colorless gas that is produced by burning fossil fuels and smelting sulfur-containing ores. It is used to preserve foods but can also cause respiratory issues in humans. The largest sources of SO2 emissions are coal burning power plants and oil refineries. SO2 dissolves in water to form acid rain, which can harm aquatic ecosystems and corrode infrastructure. Strict air quality standards regulate allowable SO2 concentrations to protect public health.

2. Sulphur Dioxide (SO₂)
Zameer Ahmed
Chemical Engineer

3. Introduction
• Sulfur Dioxide (SO2) is a colorless gas, belonging to the
family of gases called sulfur oxides (SOx). It reacts on the
surface of a variety of airborne solid particles, is soluble in
water and can be oxidized within airborne water droplets.

4. Introduction
• It is the chemical compound with the formula SO2.
• It is a toxic gas with a pungent, colorless irritating smell, that is
released by volcanoes and in various industrial processes.
• Since coal and petroleum often contain sulfur compounds, their
combustion generates sulfur dioxide unless the sulfur compounds
are removed before burning the fuel.
• It is used to preserve foods.
• It is one of a group of sulfiting agents, used in wine, on many dried
fruits and in numerous other foods.
• Sulfur dioxide is formed when sulfur-containing fuels, such as coal
and oil, are burned.

5. Natural Sources
Natural sources of sulfur dioxide include releases from
volcanoes, oceans, biological decay and forest fires. The
most important man-made sources of sulfur dioxide are
fossil fuel combustion, smelting, manufacture of sulfuric
acid, conversion of wood pulp to paper, incineration of
refuse and production of elemental sulfur. Coal burning is
the single largest man-made source of sulfur dioxide
accounting for about 50% of annual global emissions, with
oil burning accounting for a further 25 to 30%

6. Sources of Sulfur dioxide
Sulfur dioxide, SO2, is a colorless gas or liquid with a strong,
choking odor. It is produced from the burning of fossil fuels
(coal and oil) and the smelting of mineral ores (aluminum,
copper, zinc, lead, and iron) that contain sulfur. Sulfur dioxide
dissolves easily in water to form sulfuric acid.
Erupting volcanoes can be a significant natural source of
sulfur dioxide emissions.

8. Sources of SO2 emissions
• Source of sulfur dioxide emissions (data for electric utilities and
point sources are from the 2009 Minnesota Emissions Inventory;
other data are from the 2005 inventory)The Minnesota Criteria
Pollutant Emissions Inventory includes emissions from four
principal sources:
• Nonpoint sources: Smaller stationary sources such as dry
cleaners, gasoline service stations and residential wood burning.
May also include diffuse stationary sources such as wildfires and
agricultural tilling.

9. Sources of SO2 emissions
• On-road vehicles: Vehicles operated on highways, streets and
roads.
• Point sources: Large, stationary sources with relatively high
emissions, such as electric power plants and refineries.
• Non-road sources: Off-road vehicles and portable equipment
powered by internal combustion engines. Includes lawn and
garden equipment, recreational equipment, construction
equipment, aircraft and locomotives.
• Point sources are estimated annually, while the other categories
are estimated every three years.

10. Health Effects
The major health concerns associated with exposure to
high concentrations of sulfur dioxide include effects on
breathing, respiratory illness, alterations in pulmonary
defenses, and aggravation of existing cardiovascular
disease. In the atmosphere, sulfur dioxide mixes with
water vapor producing sulfuric acid. This acidic pollution
can be transported by wind over many hundreds of miles,
and deposited as acid rain.

11. Health Effects
• Sulfur dioxide affects the respiratory system, particularly
lung function, and can irritate the eyes.
• Sulfur dioxide irritates the respiratory tract and increases
the risk of tract infections. It causes coughing, mucus
secretion and aggravates conditions such as asthma
and chronic bronchitis.

12. Health Effects
• Sulfur dioxide affects the respiratory system, particularly
lung function, and can irritate the eyes.
• Sulfur dioxide irritates the respiratory tract and increases the
risk of tract infections. It causes coughing, mucus secretion
and aggravates conditions such as asthma and chronic
bronchitis.

14. Environmental effects
When sulfur dioxide combines with water and air, it forms
sulfuric acid, which is the main component of acid rain. Acid rain
can:
• cause deforestation
• acidify waterways to the detriment of aquatic life
• corrode building materials and paints.
In Queensland, there is less heavy industry than in Europe or
North America, where the potential for forming acid rain from
sulfur dioxide emissions is higher. Our weather conditions and
low sulfur content of fuels reduce the potential for acid rain.

16. Air quality standard
The recommended air quality standards for sulfur dioxide are:
• 0.20 parts per million (ppm) for a 1-hour exposure period
• 0.08ppm for a 24-hour exposure period
• 0.02ppm for an annual exposure period.
These standards are designed to protect sensitive individuals,
such as children and asthmatics.
Significant concentrations of sulfur dioxide are only measured
in Queensland near large industrial sources.

17. Emissions Control Technologies
• The two major emissions control methods are sorbent injection and flue gas
desulfurization:
1. Sorbent injection involves adding an alkali compound to the coal
combustion gases for reaction with the sulfur dioxide.Typical calcium
sorbents include lime and variants of lime. Sodium-based compounds are
also used. Sorbent injection processes remove 30–60% of sulfur oxide
emissions.
2. Flue gas desulfurization may be carried out using either of two basic FGD
systems: regenerable and throwaway. Both methods may include wet or
dry processes. Currently, more than 90% of utility FGD systems use a wet
throwaway system process.

18. Sulfur dioxide analyser

19. Measuring sulfur dioxide
• A sulfur dioxide analyzer.
• The sample (shown by the path of the blue dot) is drawn into the
analyser by means of the vacuum pump, firstly through a filter to
remove particles, and then through a scrubber to remove
interfering gases, such as hydrocarbons.
• The scrubbed sample passes into a reaction chamber where it is
irradiated with ultraviolet (UV) light at 214nm (nanometers)
generated by a zinc discharge lamp and a UV band pass filter.

20. Measuring sulfur dioxide
• Sulfur dioxide absorbs UV radiation at wavelengths between 200nm
and 240nm. Emission of fluorescence (light-producing) photons at
higher wavelengths (around 350nm) follows this absorption of UV
radiation by the molecule.
• This fluorescence is measured perpendicular to the beam using a
photomultiplier (PM) tube and the signal converted to a
concentration value.
• The measured fluorescence is directly proportional to the
concentration of sulfur dioxide in the sample.