Development and Optimization of a Low-Detection Limit Array-Type Beta Attenuation Monitor
I-CHEN CHANG, Qi-Xiang Li, Chih-Wei Lin, Sheng-Hsiu Huang, Chih-Chieh Chen, National Taiwan University
Abstract Number: 163
Working Group: Instrumentation and Methods
Abstract
Purpose:
The Beta Attenuation Monitor (BAM) is widely used for real-time ambient PM2.5 monitoring. However, its typical detection limit (4 – 4.8 μg/m³) is close to the WHO guideline of 5 μg/m³, limiting its effectiveness in low-concentration environments and health-related assessments. This study aims to develop a home-made array-type sampling BAM with an improved detection limit by enhancing sampling efficiency, reducing particle loss, and increasing beta signal strength through design optimization.
Method:
The system integrates a 1-to-4 split-flow sampling tube and a redesigned filter holder. Within a controlled particle generation system, the particle penetration efficiency and size distribution uniformity across the four sampling branches were evaluated. The filter holder was modified to optimize beta particle transmission. Signal attenuation was converted to mass concentration using the Lambert-Beer law, and data smoothing was applied through a moving average method. Key performance metrics—counts per second (CPS), response time, signal-to-noise ratio (S/N), and detection limit—were assessed and compared with those of a commercial BAM.
Result:
The split-flow sampling system achieved approximately 98% penetration efficiency for particles smaller than 3.625 μm, with inter-branch size distribution variation below 9.8%. The redesigned filter holder increased beta signal strength by 10%. A four-unit BAM array effectively reduced data fluctuation, response time, and detection limit under an S/N ratio of 10.
Conclusion:
The array-type BAM successfully reduced the detection limit from 10 μg/m³ to 3 μg/m³ while maintaining uniform sampling and particle integrity. This system offers improved speed and sensitivity, enhancing its utility for accurate and responsive PM2.5 monitoring.