TPS 901: Indoor air pollution, Exhibition Hall, Ground floor, August 28, 2019, 3:00 PM - 4:30 PM Background: Epidemiological studies of fine particulate matter (PM2.5) typically use ambient measurements as exposure proxies among local people near coal-fired power plants. There might be an error in defining the measurement as personal exposure due to far distance between ambient measurement point and indoor environment among local residents. We aimed to measure the indoor PM2.5 exposure level and to evaluate how it relates to the outdoor air quality of residents near coal-fired power plants. Methods: We measured PM2.5 data at home among 6 residents near coal-fired power plants in 3 different regions, Korea. Each participant underwent 24-hour sampling for 28 days (June 8 to July 5 in 2018). We collected the data on nearest national ambient measurement station, weather data, and total suspended particles (TSP) data from real-time telemonitoring system (TMS) of chimney at coal-fired power plants during the same period. Results: Median(Min-Max) of indoor PM2.5 concentration(µg/m3) were 12.6(2.3-38.2) in region A, 13.4(3.1-32.8), 14.3(3.1-41.2) in region B, 11.9(2.8-78.3), 16.6(3.2-83.6), 9.8(2.5-33.4) in region C.And 18.0(1.0-64.0), 15.0(1.0-63.0), 18.0(1.0-59.0) in outdoor region A, region B, region C, respectively, The correlation coefficient(p-value) of indoor and outdoor PM2.5 concentration were 0.537(<0.001) in region A; 0.571(<0.001), 0.724(<0.001)in region B; 0.435(<0.001), 0.656(<0.001), 0.685(<0.001)in region C. Those of indoor PM2.5 concentration and tsp concentration were 0.024(0.212) in region A; 0.021(0.001), 0.053(0.402) in region B; 0.366(0.002), 0.533(0.095), 0.408(0.047) in region C. Conclusion: The correlation between PM2.5 concentration of indoor and outdoor showed moderate, but low with tsp from TMS. Further study is needed to consider other indicators related to indoor air pollutants concentration using indoor exposure meter reflect real life environment.