Crowcon - Detecting Gas Saving Lives
22 March 2022
Understanding Air Pollutants: A Guide to Sulphur Oxides (SOx)

What are Sulphur Oxides (SOx)

Sulphur oxides (SOx) are compounds of sulphur and oxygen molecules. The group known as sulphur oxides consists of gases such as sulphur dioxide, sulphur trioxide and sulphur monoxide. Sulphur dioxide (SO2) is the predominant form found in the lower atmosphere, a colourless gas which freely dissolves in water and has a pungent odour.


The main source of emissions of sulphur oxides is the burning of fossil fuels. Sulphur dioxide sources commonly stem from electric industries that burn fossil fuels, as well as from petrol refineries and cement manufacturing. Some sulphur oxides are emitted into the atmosphere from natural sources such as volcanoes, however the vast majority of SOx emissions are anthropogenic (originating in human activity).

According to DEFRA, the largest sources of SO2 emissions in 2019 originated from domestic combustion (28 percent), manufacturing industries (23 percent) and energy production and transformation (23 percent). Emissions from energy production have greatly decreased in recent decades for a number of reasons including the closure of coal plants and increasing restrictions on sulphur content in fuels.

Environmental Impact

Sulphur oxide emissions are known to cause adverse impacts to vegetation, forests and agricultural crops. Sulphur dioxide emissions can also affect building stone and ferrous and nonferrous metals. Sulphurous acid, produced from hydration of sulphur dioxide, is harmful as it accelerates the corrosion of iron, steel, and zinc thereby reducing strength and longevity of some structures. SOx can also concentrate close to ground level and cause smog/fog. During the Great Smog of London in 1952, lasting for five days, levels of sulphur dioxide reached highs of 3,500 µg/m3 (averaged over 48 hours). This event was a catalyst for the implementation of the Clean Air Act 1956.

Health Impact

Humans may be exposed to SOx by breathing, drinking or eating the substance as well as by skin contact. The adverse health effects of SOx, as with most air pollutants, are dependent on factors such as duration and amount of exposure. The impact of sulphur dioxide is harmful to health as it causes irritation to the nose and throat. Exposure to high levels can cause nausea, vomiting, stomach pain and corrosive damage to the airways and lungs, with long-term inhalation exposure causing chronic breathing difficulties. SOx also contributes to the formation of particulate matter (PM) pollution by reacting with other compounds in the air. The elderly, children and those with pre-existing respiratory conditions such as asthma are particularly at risk from the effects of SOx exposure.

How SOx Can Be Measured

Fluorescence measurements, infrared absorption measurements and electrochemical measurements. We chose the electrochemical measurement technique due to its robustness and the long term accuracy which allows extension of the necessary calibration interval.

Sensit by Crowcon – RAMP

The RAMP is a robust, remote and reliable low-cost air quality monitoring platform. The device is capable of monitoring up to five gaseous chemical pollutants and the electrochemical sensors offer PPB, parts per billion, resolution for both SO and SO2 along with other common air pollutants.

The RAMP is suitable for use in a variety of industries including construction, transport, waste, oil and gas, chemical and petrochemical industries.

To find out more about Crowcon’s Air Quality solution visit

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