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Air pollutants: Sulfur Dioxide

What is sulfur dioxide?

Sulfur dioxide (sulphur dioxide in British English) is the greatest concern for the larger group of gaseous sulfur oxides (SOx). All standards and control measures for SO2 include all sulfur oxides, as sulfur dioxide is used as the indicator due to it has a major presence in the air.

Its chemical formula is SO2, it is invisible and has a nasty, pungent, irritating and sharp smell. Sulfur dioxide easily reacts with other substances to form harmful compounds, such as sulfuric acid, sulfurous acid and sulfate particles.

Sulfur dioxide is used in a big variety of situations, for example:

  • To produce acid sulfuric, through a method called contact process.
  • To preserve dried apricots, figs or other fruits.
  • Used as an antibiotic and antioxidant in winemaking.
  • To decolorize substances like swimming pool water, where the blue color of chlorine is removed.

Despite it is a toxic gas, sulfur dioxide is used in many more situations and it has a huge presence in our daily lives.

Sulfur dioxide sources

About 99% of sulfur dioxide emissions are produced by industrial activities, such as generation of electricity from coal, oil or gas. It is also produced in the burning of fossil fuels on industrial facilities, by the extraction of metal from ore or by vehicles such as cars, ships or locomotives that burn fuel.

Naturally, SO2 is formed by volcanic eruptions in active volcanoes. However, it is interesting to know there is a high presence of SO2 emissions on Venus, Mars and Jupiter, being one of the most significant gases in those atmospheres.

volcanic emissions

What are the health and environmental effects of sulfur dioxide pollution?

Sulfur dioxide, as well as the others sulfur oxides, have huge impact on the environment and dangerously affect humans, both quite similarly to what other criteria pollutants do.

How SO2 can affect humans health?

Sulfur dioxide is such a toxic gas that you can feel the firsts symptoms just 10 to 15 minutes after breathing it. Short-term exposure causes problems to the respiratory system, such as breathing difficulties, nose and throat irritating, coughing, wheezing and shortness of breath.

Sensitive groups such as elderly, children or asthmatics will notice strongest symptoms and effects. They are also more susceptible to develop diseases, in case they do not have them yet.

High concentrations of SO2 in the atmosphere commonly create other SOx, which react at the same time with other compounds to form small air pollution particles (PM). As a result, long-term exposure can seriously damage your lungs since particulate matter can penetrate deeply into our organisms.  

Since one of its uses is to preserve food, bad production process could provoke poisoning due to sulfur dioxide ingestion. Be careful when you buy it!

Which is sulfur dioxide pollution impact on environment?

This series of events and reactions from sulfur dioxide and other sulfur oxides to create particulate matter may drive to reduce the visibility in open spaces and produce haze. The deposition of these particles may damage stones, buildings, statues and monuments.

High concentrations of SOx can be harmful for vegetation foliage and growth, and can contribute to acid rain formation, which causes several issues on sensitive ecosystems.

plants problems because sulfur dioxide emissions

What is being done to reduce sulfur dioxide pollution?

Over the years, developed countries have reached some agreements to control pollution. Each country or state has its own implementation plan. For example, the Clean Air Act made by the U.S. Environmental Protection Agency (EPA) establishes National Ambient Air Quality Standards (NAAQS) for those criteria pollutants considered most harmful for health and the environment. Another example is the European Union Air Quality Directive by the European Environmental Agency, which also establishes some standards and tips to reduce air pollution, both indoors and outdoors.

Sulfur dioxide, thanks to its high toxicity and danger for humans and environment, is considered both a primary and secondary criteria pollutant. Maximum permitted or recommended levels for SO2 are:

  • It has not World Health Organization (WHO) guidelines in the last edition.
  • NAAQS: 75 ppb per hour and 0.5 ppm (1,300 μg/m³) every 3 hours (which cannot be exceeded more than once per year).
  • EU Air Quality Directive: 250 μg/m³ each hour and 125 μg/m³ daily, what cannot be exceeded more than 24 and 3 times per year respectively.
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