Decomposition of VOCs using serial surface dielectric barrier discharge reactors.

Decomposition of two typical volatile organic compounds (VOCs): toluene and methyl ethyl ketone (MEK), was investigated by introducing the complete energy yield (i.e. amount of VOCs totally converted to CO and CO2 for every 1 kWh of electrical usage) and specific energy density (SED) for the non-thermal plasma technology. Three dielectric barrier discharge reactors of which SED range was 55 J/L to 283 J/L at a flow rate of 1 L/min were connected in a 3-reactor arranged in series using interconnecting tubes in the inlets and outlets. As a result of the serial reactor design, the energy efficiency of the system improved, and in particular, 7% of increase was found in at the same level of energy consumption. The mixed phase of VOCs (toluene and MEK) showed MEK as a limiting species in this study. As the inlet concentration rose from 20 to 100 ppmv, both energy yield and complete energy yield increased from 0.8 to 9.2 g/kWh and from 0.8 to 2.3 g/kWh, respectively.

Characterization and source identification of fine dust in Seoul elementary school classrooms.

To evaluate the level of fine particulate matters in elementary schools located in a high traffic area of Seoul and verify the emission source, a field study on the classrooms was conducted under the uncontrolled condition. The indoor PM2.5 was lower than that of the outdoors as indicated by an I/O ratio of 0.52-0.92 based on mass concentration, and it was maintained below the National Guideline. Heavy metals such as Cr, Mn, Ni, Cu, Zn, As, Sn and Pb were lower in indoor PM2.5 than outdoors. On the contrary, carbons including OC and EC were higher in indoor PM2.5. As a result of source apportionment analysis, an outdoor emission source was responsible for 58.5% of the classroom PM2.5. This study can contribute to urban planning and school design to keep children safe from harmful environments.

Effects of air cleaners and school characteristics on classroom concentrations of particulate matter in 34 elementary schools in Korea.

Exposure to particulate matter (PM) in school environments has been associated with respiratory illnesses among children. Although using air cleaners was reported to reduce PM exposure and improve residents' health in homes, their effects in classrooms are not well understood. We examined how the use of air cleaners in classrooms and school/classroom characteristics affect the levels of indoor PM. Our environmental study included 102 classrooms from 34 elementary schools located on the mainland peninsula and an island in Korea. Indoor and outdoor PM were monitored simultaneously with portable aerosol spectrometers, and indoor gravimetric PM levels were measured with low volume, size-selective samplers during the class hours. Correlations among PM measurements were computed and final multiple regression models for indoor PM were constructed with a model building procedure. Correlation between indoor and outdoor PM2.5 (PM < 2.5 µm in aerodynamic diameter) was higher (r = 0.78, p < 0.01) than that of PM10 (PM < 10 µm) (r = 0.49, p < 0.01). School location, classroom occupant density, and ambient PM levels significantly (p-values<0.05) affected classroom PM concentrations. The adjusted PM levels in classrooms using air cleaners were significantly (p-values<0.01) lower by approximately 35% than in classrooms not using them. However, air cleaners appeared to remove PM2.5 more effectively than PM10, perhaps because coarse particles settle more rapidly than fine particles on surfaces, or their resuspension and generation rate by occupants exceeds the removal rate by air cleaners. Our study suggests that routine cleaning to remove surface dust along with the use of air cleaners might be required to effectively reduce occupants' exposure in classrooms.