Sulphur Dioxide Sensors | SO2 Sensor

High-Performance SO₂ Detection for Every Monitor, Every Mission

Alphasense offers a comprehensive portfolio of sulphur dioxide (SO₂) electrochemical gas sensors to support portable safety instruments, fixed installations, air quality networks, and miniature wearable devices. Designed for reliability in challenging industrial environments, Alphasense SO₂ sensors deliver fast response, excellent stability, and long operational life across a wide range of formats and performance levels.

Sensor Portfolio Overview

Portable & Industrial Safety – A-Series SO₂ Sensors

SO2-A4F – A-Series, 4-electrode PPB sensor engineered for environmental air quality monitoring, providing outstanding baseline stability and low noise.
SO2-AE – High-concentration 3-electrode SO₂ sensor (0–2000 ppm capability) for industrial safety and process applications. Based on a robust electrochemical platform suitable for portable detectors.
SO2-AF – Standard 3-electrode PPM SO₂ sensor for general industrial safety, HVAC, and emissions monitoring.

Fixed Gas Monitoring – B-Series SO₂ Sensors

SO2-B4 – B-Series, 4-electrode PPB sensor for fixed air quality networks, offering long-term stability and low drift.
SO2-BE – High-concentration 3-electrode SO₂ sensor for fixed and portable industrial safety devices.
SO2-BF – Standard 3-electrode PPM sensor offering stable SO₂ measurement for process control and environmental monitoring.

Miniature & Wearable – D-Series and H-Series SO₂ Sensors

SO2-D4 – Miniature 3-electrode SO₂ sensor designed for clip-on personal detectors and compact devices. Ideal for space-limited applications requiring 0–20 ppm SO₂ monitoring.
SO2-H4 - H-Series package, low profile SO₂ sensor for clipped and personal monitors. Suitable for personal safety applications.

Dual Gas SO₂Sensors – Space Saving Corrosion Gas Monitoring

SOH-A2 – Measures both SO₂ (0–20 ppm) and H₂S (0–100 ppm) simultaneously for corrosive sulphur gas discrimination.

Integrated Smart Technology (IST) Versions

On-sensor memory for calibration data
Temperature measurement
Plug-and-play integration
Enhanced noise and drift performance

IST versions simplify OEM integration by providing digital outputs and eliminating the need for external temperature compensation.

Choosing the Right SO₂ Sensor

High-Resolution / Low-Range (PPB)

SO2-A4F – Portable and handheld air quality instruments.
SO2-B4 – Fixed air quality networks.

General Industrial Safety (0–20 / 0–100 ppm)

SO2-AF – Portable general safety
SO2-BF – Fixed safety and process control.
SO2-D4 – Miniature personal safety devices.
SO2-H4 – Wearable/Clip-on personal safety devices.

High-Range / Industrial Process (up to 2000 ppm)

SO2-AE – Portable/process applications.
SO2-BE – Fixed installations requiring extended range.

Key Benefits Across the SO₂ Portfolio

Fast T90 response for rapid worker safety alerts.
Proven stability in high humidity and harsh environmental conditions.
Low drift and long operational life across all formats.
PPB-level options with 4-electrode designs for air quality.
Multiple mechanical formats to match any OEM instrument architecture.

Why OEMs Choose Alphasense

Alphasense SO₂ sensors are built upon decades of performance data and industry-trusted electrochemical platforms. Manufacturers choose Alphasense for:

Reliable batch consistency
Industry-leading stability in real-world environments
Robust supply chain and long sensor lifecycles
Technical support for OEM development

How SO₂ Sensors Work

Alphasense SO₂ sensors use electrochemical amperometric technology to convert SO₂ gas concentration into a measurable electrical signal.

Electrochemical cell
Each sensor contains an electrochemical cell where SO₂ participates in a controlled reaction at the working electrode. The sensor is designed so that the reaction rate is proportional to the SO₂ concentration at the electrode surface.

Amperometric measurement
Amperometric sensors operate by measuring the current produced by the electrochemical reaction at the working electrode. An external potentiostat circuit is required to measure the current between the working electrode, counter electrode and reference electrode.

In a three-electrode sensor, each electrode has a specific use:

Working electrode – designed to optimise the oxidation or reduction of the toxic gas to be measured.
Reference electrode – keeps working electrode at required potential – Bias voltage.
Counter electrode – balances the reaction of the working electrode

Depending on the measured gas, the Working electrode either oxidizes or reduces gas.

In a four-electrode sensor, an additional auxiliary electrode is used:

Auxiliary electrode -Baseline correction for Zero Current and Temperature shifts that are critical for PPB sensors

Signal output to the instrument
The resulting current (or corresponding voltage, depending on the front-end electronics) is proportional to the SO₂ concentration. This signal is then read by the instrument’s analogue front-end or digital electronics which apply calibration data to display SO₂ readings to the user.
Filtering and cross-sensitivity control
The SO₂ sensors incorporate internal filters and/or specific electrode designs to reduce cross-sensitivities to other gases such as CO, NO₂, NO, H₂S and H₂.

Together, this architecture delivers a compact, low-power sensing solution for both worker-safety instruments and R&D-grade analyzers that demand stable, repeatable SO₂ measurements.

Why Measure SO₂ Gas?

Sulphur dioxide is a corrosive, toxic gas produced in combustion, industrial processing, smelting, and fuel handling. Exposure can lead to respiratory irritation, lung damage, and acute safety hazards. Accurate SO₂ monitoring is essential for:

Worker protection in confined and industrial spaces
Environmental regulatory compliance
Process control in combustion and chemical operations
Indoor air quality and HVAC monitoring