Sulfur Dioxide Sensors
Select SO₂ sensors for portable safety, fixed industrial detection, ambient air quality, factory fenceline monitoring and combustion or process applications. Compare ppm electrochemical cells, ppb environmental modules, high-range sensors and sulfur-gas interference control.
Choose the SO₂ sensor around the measurement task
Sulfur dioxide is measured from ppb-level ambient air to multi-thousand-ppm process gas. The sensor format, electronics and sampling system should change with that concentration range.
0–20 / 50 ppm
Use a compact 3-electrode electrochemical cell with fast T90 and predictable cross-sensitivity.
- Portable multi-gas detector
- Confined-space / industrial hygiene
0–20 / 100 ppm
Fixed instruments benefit from larger electrolyte volume, stable baseline and application-specific interference filters.
- Refineries, smelters, sulfur processes
- Calibration access and enclosure diffusion
0–1 ppm / ppb-oriented
Low noise and zero stability are more important than a wide full scale. Use 4-electrode sensors or conditioned environmental modules.
- Urban monitoring
- Portable air-quality instruments
Low ppm / ppb
Outdoor monitoring needs temperature compensation, humidity control and stable baseline across daily weather changes.
- Fugitive emissions
- Unorganized emission monitoring
2,000–10,000 ppm class
Use an extended-range cell or dedicated analyzer after suitable sample conditioning when SO₂ is part of flue or process gas.
- Boilers and combustion
- Marine exhaust / sulfur processes
SO₂ + NO₂ + O₃ + CO
A conditioned multi-gas module can shorten development time for compact environmental stations and portable monitors.
- UART / RS485
- Optional PM and T/RH integration
3-electrode for ppm safety, 4-electrode for low-level SO₂
Most compact SO₂ sensors use amperometric electrochemical technology. Sulfur dioxide reaches the working electrode, produces a concentration-related current, and the instrument converts that current into a ppm or ppb value.
3-electrode EC
The standard architecture for portable and fixed ppm-level SO₂ detection.
Best fit: industrial safety and general process monitoring.4-electrode EC
An auxiliary electrode provides baseline information that can be used to compensate environmental zero changes.
Best fit: ambient and fenceline ppb-level monitoring.Filtered EC
Internal filters can suppress gases such as H₂S or HCl where the application gas mixture would otherwise bias the SO₂ channel.
Best fit: mixed sulfur-gas environments.Conditioned module
The cell is combined with AFE, compensation, processor and UART / analog output.
Best fit: environmental OEM and faster integration.SO₂ sensors for safety, ambient and high-range OEM designs
The shortlist mixes ppm safety cells, ppb environmental sensors, filtered products and extended-range process options. Compare each product against the concentration and gas matrix it was designed to handle.
| OEM need | Manufacturer | Model | Type | Published range | Key engineering point | Official source |
|---|---|---|---|---|---|---|
| Compact ppm safety | Winsen | ME3-SO₂ | Electrochemical | 0–20 ppm max 150 ppm | 20 mm format, 0.1 ppm resolution, T90 <30 s and 2-year anticipated life. | Official ↗ |
| Standard industrial SO₂ | Winsen | ME4-SO₂ | Electrochemical | 0–20 ppm max 200 ppm | 32 mm format, 0.1 ppm resolution, T90 ≤30 s and 2-year published life. | Official ↗ |
| Portable / fixed general safety | Alphasense | SO2-AF | 3-electrode electrochemical | 0–50 ppm | T90 <35 s, ppm-level A-Series format and >24-month warranted operating life. | Official ↗ |
| Portable / fixed with H₂S interference control | SENKO | SE-4SO2-20-F | Electrochemical | 0–20 ppm max overload 100 ppm | Built-in H₂S filter, <0.1 ppm typical resolution, T90 <60 s and >24-month life. | Official ↗ |
| Ambient environmental monitoring | Honeywell City Technology | A3ST/F | 4-electrode electrochemical | 0–10 ppm max 100 ppm | 4th electrode for environmental compensation; filter removes H₂S and HCl; T90 <40 s. | Datasheet ↗ |
| PPB portable / environmental SO₂ | Alphasense | SO2-A4F | 4-electrode filtered EC | 0–50 ppm | T90 <20 s, noise as low as 15 ppb, filtered design to reduce NO₂ / O₃ / Cl₂ interference. | Official ↗ |
| Conditioned ambient module | Winsen | ZE12A-SO₂ | Electrochemical module | 0–1 ppm | ≤10 ppb resolution, DAC + UART, built-in temperature compensation, T90 ≤120 s. | Official ↗ |
| Multi-pollutant environmental station | Winsen | ZEHS04 | Multi-gas electrochemical module | SO₂ + CO + NO₂ + O₃ | UART / RS485, ≤10 ppb published resolution, expandable with PM and temperature/humidity sensors. | Official ↗ |
| High-range combustion / process | Alphasense | SO2-AE | 3-electrode electrochemical | 0–2,000 ppm | Extended-range sensor with published linear output capability to 10,000 ppm and T90 <33 s. | Official ↗ |
| High-range emissions / combustion | Honeywell City Technology | 3SC | 3-electrode electrochemical | 0–2,000 ppm max 5,000 ppm | T90 <35 s, 1 ppm resolution; H₂S/HCl filtering and CO-compensation route for combustion analysis. | Datasheet ↗ |
Published values are component specifications. Confirm the latest datasheet, cross-sensitivity, sampling method and finished-instrument requirements before design freeze.
SO₂ sensor priorities change with concentration and gas matrix
Portable and fixed industrial safety
Use ppm-range cells with fast response and a well-understood interference profile. Package size and filter capacity often matter more than extreme low-level resolution.
| Model | Range | T90 | Engineering point |
|---|---|---|---|
| Winsen ME3-SO₂ | 0–20 ppm | <30 s | Compact 20 mm raw cell for portable / fixed OEM instruments. |
| Alphasense SO2-AF | 0–50 ppm | <35 s | General industrial A-Series route with stable ppm-level output. |
| SENKO SE-4SO2-20-F | 0–20 ppm | <60 s | Built-in H₂S filter for sulfur-gas mixed environments. |
Ambient air quality and fenceline monitoring
When the useful signal is measured in ppb, baseline stability, noise, temperature response and outdoor enclosure design become central.
| Product / route | Range | Architecture | Low-level point |
|---|---|---|---|
| Winsen ZE12A-SO₂ | 0–1 ppm | Conditioned EC module | ≤10 ppb resolution with DAC / UART and temperature compensation. |
| Alphasense SO2-A4F | 0–50 ppm | 4-electrode filtered EC | 15 ppb published noise and environmental baseline compensation. |
| Honeywell A3ST/F | 0–10 ppm | 4-electrode EC | Fourth electrode plus H₂S / HCl filter for ambient environmental monitoring. |
High-range combustion and process SO₂
Combustion gas can exceed a normal safety-cell range by orders of magnitude. High-range electrochemical sensors can be useful, but the sample must still be conditioned to protect measurement integrity.
| Product / family | Range class | Engineering point | Official source |
|---|---|---|---|
| Alphasense SO2-AE | 0–2,000 ppm | High-concentration electrochemical route with published linearity to 10,000 ppm. | Official ↗ |
| Honeywell 3SC | 0–2,000 ppm | 5,000 ppm maximum overload; designed around combustion / emissions standards. | Datasheet ↗ |
| Membrapor SO2/CF-2000 | 2,000 ppm class | Filtered compact sensor specifically listed for emission monitoring. | Official ↗ |
| Membrapor SO2/CF-10000 | 10,000 ppm class | Very high-range filtered option for process / emission architectures. | Official ↗ |
PPB SO₂ measurement is mainly a zero-stability problem
In urban air and factory fenceline monitoring, the target signal may be only a small fraction of the sensor's ppm full scale. Electronics noise, auxiliary-electrode correction, temperature, humidity and enclosure behavior can dominate the result.
Raw 4-electrode route
- Use the working and auxiliary channels together.
- Design a low-noise AFE with stable reference and ADC.
- Build temperature / humidity correction from controlled data.
- Use co-location or reference checks to understand field bias.
Conditioned-module route
- ZE12A provides an SO₂ 0–1 ppm channel with DAC and UART.
- ZEHS04 combines SO₂ with CO, NO₂ and O₃ for compact air-quality stations.
- Modules reduce analog development work but still need field validation.
- Outdoor enclosure airflow and condensation remain system responsibilities.
An SO₂ safety sensor is not a complete stack analyzer
A 0–20 ppm worker-safety cell is designed for clean, near-ambient gas around personnel. Raw flue gas can be hot, wet, dirty and thousands of ppm. High-range electrochemical cells can be part of an emissions instrument, but the sample architecture is just as important as the sensor.
Extract sample
Take a representative gas sample from the duct or stack.
Remove particles
Protect valves, pump and sensing surfaces from dust or ash.
Manage temperature
Bring the sample into the sensor's validated temperature range.
Control moisture
Avoid uncontrolled condensation and SO₂ loss in wet surfaces.
Measure & correct
Use the correct range and compensate known interferents where validated.
SO₂ measurement when H₂S is also present
Refineries, sulfur recovery, pulp and paper, wastewater and biogas systems can contain both oxidized sulfur (SO₂) and reduced sulfur (H₂S). The detector must distinguish them if both concentrations matter.
Internal filter
Use an SO₂ cell with a filter designed to suppress H₂S before it reaches the working electrode.
Example: SENKO SE-4SO2-20-F.Filtered environmental cell
Some ambient sensors combine a 4-electrode architecture with chemical filtering to reduce multiple interferents.
Example: Alphasense SO2-A4F.Dual SO₂ / H₂S sensor
Two independent electrochemical channels in one housing can measure both sulfur gases separately.
Example: Alphasense SOH-A2, SO₂ 0–20 ppm + H₂S 0–100 ppm.System compensation
If correction is required, validate it with the real gas mixture and sensor batch behavior rather than a generic coefficient.
Best fit: controlled analyzer designs.Wet sampling surfaces can remove SO₂ before it reaches the sensor
SO₂ dissolves readily in water. In pumped systems, condensate, wet filters and long tubing can slow the response and reduce delivered concentration.
Diffusion instruments
Place the sensing opening where representative air reaches the detector directly.
- Avoid splash and condensation on the diffusion barrier.
- Validate enclosure response, not just bare-cell T90.
Pumped instruments
Use a short sample path with materials and moisture management validated for SO₂.
- Calibrate through the same sample path where practical.
- Measure transport delay and recovery after switching back to clean gas.
Outdoor stations
Keep the sensor non-condensing while maintaining enough airflow for representative sampling.
- Temperature gradients can create condensation inside housings.
- Filters and membranes must balance particle protection against gas response.
Raw SO₂ cell, smart environmental module or multi-gas station?
Choose a raw electrochemical cell when:
- You control the analog front end and calibration.
- The final instrument needs a specific 20 mm, 32 mm or A/B-Series footprint.
- You want direct access to working / auxiliary electrode signals.
- High-volume component cost matters.
Choose a module when:
- Your host controller needs UART, RS485 or conditioned analog output.
- The project needs ppb-resolution environmental data without developing the complete AFE.
- Several pollutants must be integrated in one environmental station.
- Development speed matters more than minimum component cost.
Winsen sulfur dioxide sensors and environmental modules
Winsen covers ppm industrial SO₂ with raw electrochemical cells and low-level environmental monitoring with conditioned single- and multi-pollutant modules.
ME3-SO₂
0–20 ppm, max 150 ppm, 0.1 ppm resolution, T90 <30 s and 2-year anticipated life in air.
ME4-SO₂
0–20 ppm, max 200 ppm, 0.1 ppm resolution, T90 ≤30 s and 2-year published life in air.
ZE03-SO₂
Three-electrode electrochemical module with UART and analog voltage output. The current page directs designers to the gas-specific configuration table for final range.
ZE12A-SO₂
SO₂ 0–1 ppm, ≤10 ppb resolution, DAC 0.4–2 V and UART output, T90 ≤120 s and built-in temperature compensation.
ZEHS04
Diffusion module for CO, SO₂, NO₂ and O₃ with UART or RS485, ≤10 ppb published resolution, and expansion support for PM2.5 / PM10 / temperature / humidity.
Other sulfur dioxide sensor product ranges
These manufacturers publish SO₂ sensors for worker safety, ambient air quality, fixed monitoring and high-range process or emissions applications.
Alphasense
PPM safety, 4-electrode PPB, smart and high-range SO₂ sensors, plus dual SO₂/H₂S options.
Honeywell City Technology
Environmental 4-electrode A3ST/F and high-range 3SC combustion / process SO₂ cells.
SENKO
Filtered 0–20 ppm SO₂ sensor for portable and fixed safety detectors.
Membrapor
Compact SO₂ cells covering low concentration through 10,000 ppm filtered emission-monitoring ranges.
Submit an SO₂ sensor
Manufacturers can provide an official product page and current datasheet for inclusion.
Calibrate SO₂ through the gas path the instrument actually uses
Reactive-gas calibration should verify more than the bare cell. Regulators, tubing, filters, moisture control and enclosure flow can all change the concentration delivered to the sensor.
Bump test
Checks that target gas reaches the detector and the measurement / alarm chain responds.
Span calibration
Uses certified SO₂ gas to establish or adjust response. Allow enough time for the complete gas path to stabilize.
Filter service
Where an H₂S or acid-gas filter is part of the sensor architecture, include filter capacity and exposure history in maintenance planning.
Sulfur dioxide sensor questions
What SO₂ sensor range is common for industrial safety?
Portable and fixed toxic-gas detectors commonly use sensors in the 0–20 ppm or 0–50 ppm class. The correct range should cover the alarm region and credible upset concentration without sacrificing the low-level resolution needed for the instrument.
What is different about an ambient air-quality SO₂ sensor?
Ambient monitoring works at much lower concentration than typical industrial safety. It needs low noise, stable zero, temperature compensation and often a 4-electrode electrochemical architecture or conditioned module capable of ppb-level resolution.
Can a 0–20 ppm SO₂ safety sensor be used directly in stack gas?
Not for raw high-concentration flue gas in most cases. Stack and combustion measurements may require hundreds or thousands of ppm range plus cooling, particulate removal, moisture management and controlled sample delivery before the sensor or analyzer.
Why is H₂S interference important in SO₂ sensing?
SO2 and H2S can occur together in refineries, biogas, pulp and paper and other sulfur-process environments. Some SO2 sensors use an internal H2S filter; dual SO2/H2S sensor designs are also available when the instrument must distinguish both gases.
When should I use a 4-electrode SO₂ sensor?
Use a 4-electrode design when baseline compensation and low-level stability are important, especially for ambient or fenceline monitoring. A standard 3-electrode cell is normally sufficient for ppm-level worker-safety instruments.
How does condensation affect SO₂ measurement?
SO2 is highly soluble in water. Condensate and wet sample surfaces can remove SO2 from the gas stream, slow the response and change the concentration reaching the sensor. Keep the gas path non-condensing or condition the sample in a controlled way.
Should I choose a raw SO₂ sensor or a module?
Choose a raw electrochemical element when your team will design the analog front end, calibration and temperature compensation. Choose a module when digital or analog concentration output and shorter integration time are more valuable.
How should SO₂ sensors be calibrated?
Use certified SO2 calibration gas and a gas-delivery system suitable for reactive gases. Minimize tubing length and wet surfaces, use compatible regulators and fittings, and allow the complete detector or sample path to stabilize before adjusting the span.
Final checks before design freeze
Validate the complete SO₂ instrument at the concentration, humidity, temperature and gas mixture expected in service. The sensor datasheet defines the component; the enclosure and sample path define how that component sees the gas.
- Separate worker-safety, ambient-air and process-emissions measurement requirements.
- Confirm range, overload, T90 and recovery after high SO₂ exposure.
- Review H₂S, NO₂, O₃, Cl₂ and other relevant cross-sensitivities.
- Use 4-electrode / compensated designs where ppb baseline stability is required.
- Keep condensation and uncontrolled wet surfaces out of reactive-gas sample paths.
- Validate filters, tubing and gas conditioning using target gas.
- Confirm the applicable safety, ambient-air or emissions requirements for the finished instrument.
Need an SO₂ sensor for an OEM project?
Send the target range, safety / ambient / emissions application, gas mixture, operating environment, sampling method and output interface. Manufacturers can also submit SO₂ sensor models with an official product page and current datasheet.
Specifications and product availability can change. Confirm the latest manufacturer datasheet before engineering, compliance or purchasing decisions.