Comparison of Personal or Indoor PM 2.5 Exposure Level to That of Outdoor: Over Four Seasons in Selected Urban, Industrial, and Rural Areas of South Korea: (K-IOP Study).

This study aimed to compare the distribution of indoor, outdoor, and personal PM 2.5 (particulate matter ≤ 2.5 μm) hourly concentrations measured simultaneously among 81 nonsmoking elderly participants (65 years or older) living in urban, industrial, or rural areas over 4 seasons (2 weeks per season) from November 2021 to July 2022). PM 2.5 measurements were conducted using low-cost sensors with quality control and quality assurance tests. Seasonal outdoor PM 2.5 levels were 16.4 (9.1-29.6) μg/m 3 , 20.5 (13.0-38.0) μg/m 3 , 18.2 (10.2-31.8) μg/m 3 , and 9.5 (3.8-18.7) μg/m 3 for fall, winter, spring, and summer, respectively. For indoor PM 2.5 , the median seasonal range was 5.9-7.5 μg/m 3 , and the median personal PM 2.5 exposure concentration was 8.0-9.4 μg/m 3 . This study provided seasonal distributions of IO (ratio of indoor to outdoor PM 2.5 concentration) and PO (ratio of personal to outdoor PM 2.5 concentration) using a total of 94,676 paired data points. The median seasonal IO ranged from 0.30 to 0.51 in fall, winter, and spring; its value of summer was 0.70. The median PO by season and study area were close to 1.0 in summer while it ranged 0.5 to 0.7 in other seasons, statistically significantly lower ( p < 0.05) than that in summer. Our study has revealed that the real-world exposure level to PM 2.5 among our elderly study participants might be lower than what was initially expected based on the outdoor data for most of the time. Further investigation may need to identify the reasons for the discrepancy, personal behavior patterns, and the effectiveness of any indoor air quality control system.