This study investigates the effect of machine translation (MT) use on the writing performance of Korean EFL students, focusing on complexity, accuracy, and fluency (CAF). Six participants completed a series of writing tasks in which they first translated their L1 writing into L2 manually and then used MT to revise their L2 drafts. This process was repeated across ten different writing topics. Participants’ drafts were analyzed using CAF measures to assess MT’s impact on their writing performance and observe changes over tasks. The results show that MT significantly improved accuracy and fluency. However, gains in syntactic and lexical complexity were less evident. While group-level analysis showed consistent progress, individual trajectories varied widely, indicating diverse patterns of development. Overall, the findings suggest that MT enhances writing accuracy and fluency among Korean EFL students, although its impact on syntactic and lexical complexity is limited. These results indicate that MT can serve as a valuable tool for self-directed learning, helping students independently improve their writing accuracy and fluency and develop essential self-editing skills. This study highlights the potential of MT as a supplementary tool to support EFL students’ writing development, along with traditional instruction.

Outdoor air pollution with particulate matter has become more severe in Korea. Ambient particle concentration affects the indoor environment through various routes through building envelopes. In this study, we investigated particle exposure in residential buildings. Indoor and outdoor particle sources determined the indoor concentrations and particle exposure. This paper measured indoor particles and CO2 concentrations in two different apartment buildings and conducted the survey for 24 hours. The I/O ratio of the occupant awake period was higher than the asleep period. The I/O ratio in the awake period is 0.93-3.65, while the I/O ratio in the asleep period is 0.31- 0.76.Indoor peak events such as cooking or cleaning temporarily increase the I/O ratio and emit the indoor particle sources. Decay rate constant is 0.49-6.84 (1/h) in the indoor peak events during the operation of the exhaust hood and natural ventilation. The size range of 0.3-0.5 μm size is over half for the proportions of emitted particles (55.6%). Daily exposure is divided into indoor sources (45.2%) and outdoor sources (54.8%). We found the differences for the proportion of particle exposure. The ratio of daily exposure in particles for 0.3-0.5 μm size is 43.1 (indoor)/ 56.9 (outdoor) %. However, indoor sources are higher than outdoor sources for the ratio of daily exposure in particles for the 0.5-10.0 μm size.