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 PM 2.5 (PM < 2.5 μm in aerodynamic diameter) was higher (r = 0.78, p < 0.01) than that of PM 10 (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 PM 2.5 more effectively than PM 10 , 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

Droplet microfluidics is a promising tool for single-cell analysis since single cell can be comparted inside a tiny volume. However, droplet encapsulation of single cells still remains a challenging issue due to the low ratio of droplets containing single cells. Here, we introduce a simple and robust single cell sorting platform based on a magnetophoretic method using monodisperse magnetic nanoparticles (MNPs) and droplet microfluidics with >94% purity. There is an approximately equal amount of MNPs in the same-sized droplet, which has the same magnetic force under the magnetic field. However, the droplets containing single cells have a reduced number of MNPs, as much as the volume of the cell inside the droplet, resulting in a low magnetic force. Based on this simple principle, this platform enables the separation of single cell-encapsulated droplets from the droplets with no cells. Additionally, this device uses only a permanent magnet without any complex additional apparatus; hence, this new platform can be integrated into a single cell analysis system considering its effectiveness and convenience.

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Open burning of solid wastes, a potential nonpoint emission source, has recently become a topic of interests, particularly in the metropolitan area of Seoul, Korea. To estimate the effects of irregular open burning on local air quality, we evaluated the emission levels of harmful substances from test combustion of individual types of domestic municipal solid waste (MSW), including paper, wood, and plastics. The emission factors of PM 10 , PM 2.5 , PAHs, and heavy metals obtained from laboratory tests differed depending on the combustion material. A brief survey of residents and local government officials showed that more than 10.6% of homes in the metropolitan area have eliminated waste by irregular burning. Based on the public survey in the test area, the average annual emissions of hazardous materials from frequent open burning was estimated to be 71 tons for PM 10 , 46.6 tons for PM 2.5 , 914 kg for heavy metals, and 67 kg for PAHs. Open burning creates nearly 0.44% of regional air pollution from PM 10 .