The Continuous Emission Monitoring System (CEMS) is mainly used for continuous monitoring of various industrial waste‑gas sources, such as thermal power plants, waste incineration plants, coal and petrochemical plants, paper mills and other industries.

With the growing severity of air pollution, governments have attached greater importance to the supervision of waste‑gas emissions from factories and enterprises. Monitoring factory flue‑gas emissions and verifying compliance with emission standards relies on CEMS. Two key objectives of CEMS are to detect the concentration of particulate matter and the content of pollutant gases. Among these gases, sulfur dioxide (SO₂) is highly harmful to the environment and requires sulfur dioxide sensors for measurement.

CEMS mainly consists of a gaseous pollutant monitoring subsystem, a particulate‑matter concentration monitoring subsystem, an emission‑flow‑parameter monitoring subsystem, and a data acquisition, processing and communication system. Monitoring of sulfur dioxide content falls under the gaseous pollutant monitoring subsystem. The sulfur dioxide gas sensor measures sulfur dioxide in treated exhaust gas to determine whether emission levels meet requirements and whether further desulfurization treatment is necessary. Meanwhile, measurement data from the sulfur dioxide sensor provides a data basis for potential follow‑up treatment and helps improve desulfurization efficiency.