During periods where a fine dust watch was announced, we measured particulate matter by the light scattering method and the gravimetric method in accordance with the application of an air cleaner in 3 homes. The first investigation showed a lower indoor particulate matter 2.5 (PM2.5) concentration distribution than normal when there was a fine dust warning. Also, it was found that the result of the second research was similar to the first research, and was the effect of an air cleaner. The result of a comparison of black carbon (BC) concentration in accordance with an air cleaner at one room showed a lower concentration distribution than normal, as in the first and the second research when there was a fine dust warning. PM2.5 risk reduction effect showed 9.09E-5 (light scattering method) ~ 9.37E-5 (Gravimetric method) and 1.71E-4 (Light scattering method) ~ 1.76E-4 (Gravimetric method). Therefore, it was found that when there was a fine dust watch without ventilation, if air cleaner with the proper capacity is used and the influx of outside air reduced, the harmful effects of the fine dust can be lessened. Keywords : PM10, PM2.5, Black carbon, Air cleaner, Risk reduction, Studio apartment