Comparison of PM2.5 Monitoring Data Using Light Scattering and Beta Attenuation Methods: A Case Study in Seoul Metro Subway

A study on monitoring PM_2.5 concentrations at an underground subway station using light scattering and beta attenuation methods was conducted. Six optical particle counters (OPCs), which were representative of the light scattering method and had 16 size channels, were installed at different sampling sites in the waiting room and platforms to compare PM_2.5 concentrations, determine PM_2.5 /PM₁₀ ratios, and characterize the size distribution based on particle number. In terms of the beta attenuation method, a beta-ray attenuation monitor (BAM) was set up at the platform to compare it with OPCs for one month. It was found that 1h-average PM_2.5 concentrations varied at different sampling sites depending on PM composition, while 24h-average PM_2.5 concentrations were independent of the sampling sites. There was a significant difference between the means of 1h-average PM_2.5 concentrations observed by the BAM and OPC when PM_2.5 contributed to less than 50% or higher than 80% of PM₁₀. In contrast, the 24h-average PM_2.5 concentrations observed by the BAM and OPC showed the same patterns as each other with an insignificant difference. Therefore, an OPC can be used to monitor the 24h-average PM_2.5 concentration in an underground subway station. However, the use of OPC to measure the 1h-average PM_2.5 concentration should consider PM composition and other factors. In addition, more frequent calibration is needed on a regular basis.