SO2 Sensors: Monitoring Sulfur Dioxide Around Power Plants and Industrial Estates
AIR QUALITY MONITORING
SO2 Sensors: Monitoring Sulfur Dioxide Around Power Plants and Industrial Estates
Sulfur dioxide is invisible, yet it harms the respiratory health of nearby communities and causes acid rain. Continuous real-time measurement lets plants and communities know in time, before harm is done.
An SO2 sensor is essential for power plants, refineries, industrial estates, and local authorities that must track air quality, both to comply with regulations and to build trust with surrounding communities, while also catching combustion problems early. This article explains where SO2 in the air comes from, why it is dangerous, what the standards are, and how to choose and install an SO2 sensor for reliable data.
Quick answer: where does SO2 in the air come from, and why is it dangerous?
Most SO2 in the air comes from burning fuels that contain sulfur, such as coal, lignite, and heavy fuel oil, in power plants, boilers, refineries, metal smelters, and ships. SO2 irritates the respiratory system and constricts the airways, hitting asthma sufferers and children hardest. It also reacts in the atmosphere to form fine PM2.5 particles and acid rain. An SO2 sensor tracks concentrations in real time and raises alerts when values exceed limits.
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Where does SO2 in the air come from?
Sulfur dioxide is a colorless gas with a sharp smell, like a freshly struck match, at high concentrations. It forms when sulfur in fuels or raw materials is burned and combines with oxygen.
| Source | Cause |
| Coal and lignite power plants | Some coal is high in sulfur; if flue gas treatment fails, large amounts of SO2 leave the stack |
| Industrial boilers | Burning heavy fuel oil or solid fuels containing sulfur |
| Refineries and petrochemicals | Sulfur removal processes and gas flaring |
| Smelters and foundries | Many metal ores contain sulfur |
| Ports and shipping | Ship engines burning high-sulfur fuel |
02
Why is SO2 dangerous?
Respiratory system
Irritates the nose, throat, and airways, causing coughing, chest tightness, and breathing difficulty, even with short exposure
Vulnerable groups
People with asthma, children, the elderly, and those with heart or lung disease are affected more severely
PM2.5
SO2 reacts in the air to form sulfate particles, part of fine particulate matter
Acid rain and crops
Damages leaves, acidifies soil and water, and speeds corrosion of metals and buildings
03
SO2 standards to know
| Type | Limit |
| Ambient air, 1-hour average | Not above 0.3 ppm (300 ppb) under Thailand's Pollution Control Department standard |
| Ambient air, 24-hour average | Not above 0.12 ppm (120 ppb) |
| Ambient air, annual average | Not above 0.04 ppm (40 ppb) |
| Workplace, 8-hour average | A few ppm, depending on occupational safety regulations |
Note that ambient standards are at ppb level, tens of times lower than workplace limits, so the SO2 sensor must match the application. Check the latest standards from the relevant authorities before citing them.
04
Types of SO2 sensors and which to choose
| Type | Strengths | Best for |
| Electrochemical | Affordable, compact, low power, and easy to connect to IoT, but cells have a limited life and need calibration | Fence-line, community, and workplace monitoring networks |
| UV fluorescence analyzer | High ppb-level accuracy and the reference method for official stations, but costly and needs a temperature-controlled shelter | Main air quality monitoring stations |
| Stack monitoring (CEMS) | Measures high concentrations directly in flue gas | Power plant and large boiler stacks |
Today's popular approach
Combine a few high-accuracy reference stations with multiple electrochemical SO2 sensors spread around the plant fence line and in the community. This gives a broad picture of how the gas disperses within a sensible budget, and reference station data can be used to check the network sensors periodically.
Specifications to check when choosing an SO2 sensor
- Range and resolution: ambient monitoring needs ppb-level resolution, while workplace use needs ppm range
- Cross-sensitivity: gases such as H2S and NO2 can skew readings; check the manufacturer's cross-sensitivity data
- Temperature and humidity compensation: hot, humid tropical air strongly affects electrochemical cells
- Cell life and calibration interval: budget for cell replacement and calibration from the start
- Output signal: RS485 Modbus-RTU or 4-20mA to connect to data loggers and IoT systems
05
Installing SO2 sensors around power plants and industrial estates
- Place sensors by wind direction: use historical wind data to find the direction in which wind most often carries stack emissions toward communities, and place sensors both downwind and upwind for comparison
- Install alongside wind sensors: when SO2 rises, wind direction and speed help identify the source
- Inlet height: at a level representative of the air people breathe, typically several meters above ground, clear of walls or trees that block airflow
- Avoid nearby local sources such as vehicle exhausts or generators, which cause spikes unrelated to the source being monitored
- Protect from sun, rain, and lightning: use a ventilated radiation shield and fit surge protection on outdoor stations
RECOMMENDED PRODUCT
Supplementary E-POWER sensor for air quality stations
Rika RK300-08 Multi-in-one Gas Sensor
A multi-gas sensor in one housing that measures PM2.5, PM10, CO, ozone, VOCs, temperature, and humidity. Install it alongside an SO2 sensor on the same station for a complete picture of air quality around the plant.
06
Real-time SO2 monitoring networks from E-POWER
E-POWER is a distributor of RIKA environmental sensors and monitoring stations, with experience installing outdoor weather and air quality station poles.
- SO2 and other gas sensors together with PM2.5, temperature, humidity, and wind sensors over RS485 Modbus-RTU
- FlowPLC / IoT Edge Gateway logs data locally, runs on solar power, and transmits over 4G or LoRaWAN
- A dashboard for every station showing 1-hour and 24-hour averages against standards, with wind direction data
- LINE or Telegram alerts when SO2 rises abnormally, so teams can check combustion processes immediately
Frequently asked questions about SO2 sensors
Where does SO2 in the air come from?
Mostly from burning sulfur-containing fuels such as coal, lignite, and heavy fuel oil in power plants, boilers, refineries, smelters, and ships.
Why is SO2 dangerous?
It irritates the respiratory system and constricts airways, especially affecting people with asthma and children, and contributes to PM2.5 and acid rain.
What are Thailand's ambient SO2 standards?
1-hour average not above 0.3 ppm, 24-hour average not above 0.12 ppm, and annual average not above 0.04 ppm. Check the Pollution Control Department's latest notification.
Are electrochemical SO2 sensors accurate enough?
They suit monitoring and alert networks when the model has adequate resolution and temperature-humidity compensation, but official reporting usually requires reference instruments.
Why measure wind direction along with SO2?
To identify which source caused an SO2 rise, and to position sensors to cover the downwind areas most affected.
Need an SO2 monitoring network around your plant or community?
E-POWER engineers can design air quality monitoring stations, from SO2 sensor selection and wind-based siting to solar power, dashboards, and mobile alerts.
Talk to us on LINE @epower info@epower.co.thTel. +66 81-559-5145 · YouTube: Epower Service · TikTok: epowerservice_
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