Suspension of particulate matter (PM) in indoor spaces, which increases risk of negative impact on occupants' health from exposure to PM, is influenced by humidity level in the indoor environment. The goal of this study is to investigate the property of size-resolved PM suspension in accordance with the relative humidity through simulation chamber experiments which reflect the indoor environmental characteristics. The relative humidity of simulation chamber is adjusted to 35%, 55% and 75% by placing it inside a real-size environmental chamber which allows artificial control of climatic conditions (e.g., temperature, humidity). At the respective humidity conditions, PM suspension concentration caused by occupant walking is analyzed by particle size (0.5-0.8, 0.8-1.0, 1.0-2.5, 2.5-3.5, 3.5-4.5, 4.5-5.5, 5.5-8.0, and 8.0-10 ㎛). Irrespective of the particle size, the suspension concentration reveals a decreasing tendency as the relative humidity increases. Furthermore, a one-way analysis of variance (one-way ANOVA) test statistically verifies that the suspension concentration has a significant difference depending on the indoor relative humidity level. In addition, as the relative humidity increases, a proportion of the suspended particles with 0.5-2.5 ㎛ diameter decreases, while that with 2.5-3.5 ㎛ diameter increases. The reason is considered that the humidity has an effect on adhesion and coagulation forces of the particles.

This study demonstrated the applicability of laser-induced breakdown spectroscopy (LIBS) to determine elements (C, H, and O) and their ratios of aerosols, enabling to discriminate various types of carbonaceous aerosols. The elements of carbonaceous aerosols which were collected on Ag membrane filter under Argon environment were successfully detected by using the LIBS. The LIBS responses (emission lines of C, H, and O in the LIBS spectra) to increasing carbonaceous aerosols were evaluated. The sensitivity of emission lines varied with different elements. Limit of detection (LOD) values for C, H, and O elements for aerosols collected on the filter were found to be 3.17 ㎍, 0.15 ㎍, and 2.25 ㎍, respectively. The spectral data (elemental ratios) obtained using LIBS were in reasonable agreements with the nominal atomic ratios (H/C and O/C) of various carbonaceous aerosols. Further, LIBS spectra were investigated by using principal component analysis (PCA) method to identify types of various carbonaceous aerosols. Our results suggested the possibility of the LIBS technique to detect and/or to discriminate various carbonaceous aerosols and to determine their elemental ratios (H/C and O/C).

In this study, an empirical study was conducted to investigate the clean air delivery rate (CADR) and the proper particle cleaned air delivery per hour (PCH) of the air cleaning device installed in passenger car cabin. Changes in internal particle concentration were measured in the cabins of the pick-up type engine-driven car and the electric vehicle depending on cabin air filters, ventilation modes, and blower settings. In the tested cars, PM_2.5 collection efficiency of the HEPA filter was higher than that of the genuine filter. The PM_2.5 collection efficiency of each cabin air filter was measured to be similar regardless of the blower setting of the tested cars. This means that the higher the blower setting, the higher the CADR and the PCH. The infiltration rate varies depending on the air tightness of the car. The cabin was more contaminated with particles under driving. From the CADRs measured inside the passenger car cabin, the recirculation mode of HVAC system is a more effective for managing ultrafine particles than the fresh air mode. From a few assumptions, the proper PCH was derived about 0.8 times/min (48 times/h). From this result and several experiments, the proper operation setting of air cleaning device installed inside cars can be found out to control indoor air quality. Also, an appropriate operation settings of HVAC system can be found with considering cooling and heating conditions for thermal comfort in passenger car cabin.

A silicon carbide (SiC) ceramic filter is an effective component for hot flue gas cleaning because of its high collection efficiency, high thermal shock resistance, and excellent mechanical strength. The effect of molding pressure in the production of SiC granular ceramic filters, on the mechanical strength and filtration performance, was investigated in this work. It was found that the ceramic filters produced at molding pressures less than 20 MPa have low mechanical strength and that this result was caused by weak physical interaction among the ceramic powders due to defects and cracks. On the other hand, the filter quality factor(q_F), which represents filtration performance of filter media, decreased with increasing the molding pressure due to the drastic increase in pressure drop. Ceramic filter performance factor(q_FM), which is the manipulation of maximum mechanical strength and q_F, was introduced to consider both mechanical strength and filtration performance in this study. As a result, molding pressure of 30 MPa was desirable to produce a SiC granular ceramic filter based on q_FM.

In this study, the performance of air cleaners installed in subway stations was evaluated using field test method and chamber test method in accordance with the standard for air cleaner. Also, the air filter maintenance period was examined by the performance reduction of air cleaners with respect to the air filter usage period. From the field tests, the clean air delivery rate (CADR) of air cleaners with filter in use was about 85% on average compared to the ones with new filter. The main factor of CADR reduction was not the decrease of filter efficiency but the decrease of airflow rate. The chamber test results shows that the CADR of air cleaners decreased with the usage time, but the proper filter replacement can make the CADR keep about 95% of the certified CADR. The expected filter replacement cycle measured by the field test method was calculated to be approximately 3.35 months (100 days). However, the replacement cycle was a large difference between 1.2 and 6.6 months with the different stations. Therefore, the replacement cycle should be individually investigated for each station. The use of air cleaners must be effective in reducing fine dust in subway stations. For more effective air quality management in subway stations, additional researches is necessary to define the appropriate capacity of HVAC system and air cleaner, and related maintenance for each station.