The significant variations of concentrations were mainly attributed to different emission strength of each facility, which was influenced by operating conditions, control devices, and diffusion conditions during sampling. The majority of samples collected inside the plants showed two to several hundred times higher total concentrations (32.1 μg m− 3, sample no. 16) than from a boundary site upwind of the industrial plant that was assumed to represent the background concentration, which suggests that the high concentrations observed in the samples were due to fugitive emissions arising from near the process facilities. We classified these high VOC concentration samples as “source samples,” and further discuss the species composition of VOC emissions in the following section. However, the VOC concentrations of truck loading (sample no. 14), railway loading (sample no. 15), and ABS wastewater treatment (sample no. 21) were comparable to or slightly higher than the background, likely because no VOC emission was released during the sampling period. These samples were not thought to capture the source emissions from the closed facilities and were thus omitted from the source samples.