VOC online monitoring deviceThe selection of detection technology directly determines the accuracy and application value of monitoring data. PID (photoionization detection), FID (hydrogen flame ionization detection), and gas chromatography (GC) are currently the mainstream technological paths. The three types of technologies are based on different detection principles, resulting in significant differences in response speed, anti-interference ability, and component resolution, and are suitable for monitoring needs in different scenarios such as chemical parks and printing workshops. Below, we will break down the differences from the core performance dimensions to provide a scientific basis for accurate selection by enterprises.

Response speed is the core indicator of real-time monitoring, and the three types of technologies exhibit gradient differences of "PID fastest, FID centered, and GC slowest". PID technology relies on ultraviolet lamps to ionize VOC molecules and generate current signals, without the need for complex preprocessing. The response time can be as low as 0.1-1 second, and it can quickly capture instantaneous fluctuations in VOC concentration. It is particularly suitable for real-time monitoring in scenarios such as leak warning in chemical parks and instantaneous emissions in printing workshops. FID ionizes VOCs through hydrogen flame, and the response time after flame stabilization is about 1-3 seconds. Although slightly slower than PID, it can still meet the real-time monitoring needs of most fixed pollution sources and is widely used in continuous emission monitoring in painting workshops. GC technology requires separation of components through chromatographic columns before detection. Due to the limitation of separation efficiency, the single detection cycle is usually 1-30 minutes, with the slowest response speed. It is more suitable for scenarios where the components are complex but do not require instantaneous monitoring, such as routine monitoring of VOCs in ambient air.

The difference in anti-interference ability lies in the sensitivity of the detection principle to impurities. FID has strong anti-interference ability, followed by PID, and GC needs to be judged based on the type of detector. FID only responds to organic compounds containing carbon, and has no signal to inorganic impurities such as water, CO, CO ₂, ammonia, etc. It can effectively avoid impurity interference and has outstanding data stability in high humidity chemical wastewater treatment stations, printing workshops containing acidic waste gas, and other scenarios. PID is affected by the energy of ultraviolet lamps and is sensitive to compounds containing heteroatoms such as sulfides and nitrogen oxides. It is prone to positive interference in the coexisting environment of multiple pollutants in chemical industrial parks, and pre-treatment devices (such as activated carbon filtration) are needed to reduce the impact of impurities. The anti-interference ability of GC depends on the supporting detector. If combined with FID detector, the anti-interference ability is equivalent to that of FID alone. If combined with PID detector, the anti-interference ability is weaker. However, through the separation effect of chromatographic column, the interference of similar organic compounds can be effectively eliminated, and the overall anti-interference scene adaptability is more flexible.

The component resolution is the key to distinguishing single VOCs from total VOCs. GC has excellent performance, while PID and FID can only achieve total monitoring. GC technology separates different VOC components through the adsorption desorption action of chromatographic columns. Combined with detectors, it can accurately identify the concentration of single substances such as benzene, toluene, and xylene. The component resolution can reach the Danak level, making it a technology for tracing characteristic pollutants in chemical industrial parks and monitoring VOC components in key enterprises. Both PID and FID belong to the "total VOC" monitoring technology and cannot distinguish specific components: PID can roughly distinguish the types of VOCs by adjusting the energy of ultraviolet lamps (such as high-energy lamps having stronger response to aromatic hydrocarbons), but cannot accurately quantify a single component; FID outputs the total concentration based on carbon content and cannot achieve component discrimination. It is only applicable to monitoring scenarios where the total VOC concentration meets emission standards.

The selection of three types of technologies should closely follow the requirements of the scenario: pursuing real-time warning and rapid response, selecting PID, such as chemical plant leak monitoring; It is necessary to monitor the total VOC in complex impurity environments using FID, such as emission monitoring in painting workshops; To achieve component traceability and precise quantification of GC, such as routine monitoring of VOCs in ambient air. In practical applications, a "combination scheme" is often used, such as the combination of GC and PID, which achieves real-time monitoring through PID and periodic component analysis through GC, balancing efficiency and accuracy.

The core of selecting VOC online monitoring technology is "scene adaptation+performance matching", where response speed determines real-time performance, anti-interference ability ensures stability, and component resolution meets traceability requirements. Enterprises need to combine monitoring purposes, types of pollutants, and environmental conditions when selecting, and if necessary, collaborate with professional technical teams to conduct on-site testing to ensure that the selected technology meets the requirements of HJ75, HJ76 and other standards, while providing accurate and reliable data support for pollution control.