Increasing concerns about the spread of airborne pathogens such as severe acute respiratory syndrome (SARS) and novel swine-origin influenza A (H1N1) have attracted public attention to bioaerosols and protection against them. The airborne pathogens are likely to be expelled from coughing or speaking, so the physical data of the exhaled particles plays a key role in analyzing the pathway of airborne viruses. The objective of this study was to analyze the initial velocity and the angle of the exhaled airflow from coughing and speaking of 17 males and 9 females using Particle Image Velocimetry (PIV) and acrylic indoor chamber. The results showed that the average initial coughing velocity was 15.3 m/s for the males and 10.6 m/s for the females, while the average initial speaking velocity was 4.07 m/s and 2.31 m/s respectively. The angle of the exhaled air from coughing was around 38° for the males and 32° for the females, while that of the exhaled air from speaking was around 49° and 78° respectively. Also, the linear relation between the tested subject's height and their coughing and speaking velocity was shown in this study.

We analyzed the size-dependent volatility of nanoparticles in a diameter range of 30-70 nm in diesel exhaust emissions. The test system included a medium-duty diesel truck on a chassis dynamometer, a single-stage dilution tunnel, a tandem differential mobility analyzer (TDMA) equipped with an electric furnace, and a condensation particle counter. The size shifts of monodispersed diesel nanoparticles under changing furnace temperatures were measured by TDMA in the gas phase. Together with the reduction of average particle size and volume, we observed the development of bimodal size distributions resulting from the separation between semivolatile and nonvolatile species as the furnace temperature was increased. While 91-98% of the particles were found to be semivolatile species by total volume during the idling engine condition, only 6-9% were semivolatile during the one-half engine load condition. We also found that smaller particles contained a larger fraction of semivolatile species.

Soil dust particles transported from loess regions of the Asian continent, called Asian dust, highly influences the air quality of north-eastern Asia and the northern Pacific Ocean. In order to investigate the effects of these dust storms on the chemical composition of atmospheric aerosol particles with different size, measurements of size distributions of total aerosol and major ion species were carried out on Jeju Island, Korea during April 2001. Juju Island was chosen for the study because the levels of emissions of anthropogenic air pollutants are very low. A 5-stage cascade impactor was used to sample size-fractionated aerosol particles. Samples were analyzed for major water-soluble ions using Dionex DX-120 ion chromatograph. The average mass concentration of total aerosol was found to be 24.4 and 108.3 microg m(-3) for non-Asian dust and Asian dust periods, respectively. The total aerosol size distribution, measured during the non-Asian dust period, was bimodal, whereas the coarse particles dominated the size distribution of total aerosol during the Asian dust period. It was found that SO4(2-), NH4+ and K+ were mainly distributed in fine particles, while Cl-, NO3-, Na+, Mg2+ and Ca2+ were in coarse particles. Although SO4(2-) was mainly distributed in fine particles, during the Asian dust period, the concentrations in coarse particles were significantly increased. This indicates heterogeneous oxidation of SO2 on wet surfaces of basic soil dust particles. The NH4+ was found to exist as (NH4)2SO4 in fine particles, with a molar ratio of NH4+ to SO4(2-) of 2.37 and 1.52 for non-Asian dust and Asian dust periods, respectively. Taking into account the proximity of the sampling site to the sea, and the observed chloride depletion, coarse mode nitrate, during the non-Asian dust period, is assumed to originate from the reaction of nitric acid with sodium chloride on the surfaces of sea-salt particles although the chloride depletion was not shown to be large enough to prove this assumption. During the Asian dust period, however, chloride depletion was much smaller, indicating coarse nitrate particles were mainly produced by the reaction of nitric acid with surfaces of basic soil particles. Most chloride and sodium components were shown to originate from sea-salt particles. Asian dust aerosols, arriving at Jeju Island, contained considerable amounts of sea-salt particles as they passed over the Yellow Sea. Ca2+ was shown to be the most abundant species in Asian dust particles.

With increasing interest in indoor air quality (IAQ), the recommended standards for the IAQ of public transportation were established in 2003 in Hong Kong and in 2007 in Korea. According to the recommended standards on the IAQ of public transportation of both Hong Kong and Korea, the air quality in the passenger cabins of railway vehicles may be improved through the ventilation system using outside air. Also, it is reasonable to use the carbon dioxide (CO 2 ) level as the index of improvement. The Korean guidelines on the air quality in cabins include the recommended standard for particulate matter 510 mm (PM 10 ) as well as CO 2 . In this study, the levels of CO 2 and PM 10 were continuously measured in the subways operated in the Seoul metropolitan area and the number of passengers using subway vehicles was surveyed based on the lines in operation and each stopping station. In addition to CO 2 and PM 10 levels, the temperature and moisture (RH%) in the passenger cabins were also measured. The average CO 2 and PM 10 levels for each line were compared with the recommended levels of cabin air quality. The correlation analysis to the number of passengers proved that the CO 2 level was linearly correlated with the number of passengers. The average CO 2 level and PM 10 level in the subway trains in the metropolitan area were found to be below that recommended in the air quality standards for cabins.

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Wall loss rates of polydispersed aerosols in a stirred vessel were studied theoretically and experimentally. A formula for the polydispersity factor of the wall loss rate was derived using the moment method of log-normal size distribution and compared with numerical calculations. The representative theory of Crump and Seinfeld (1981) was used as the wall loss rate of monodispersed aerosols in which the Brownian diffusion, the turbulent eddy diffusion, and the gravitational settling are included as wall loss mechanisms. The results of the analysis show that the wall loss rate of a polydispersed aerosol is substantially higher than that based on a monodispersed size distribution model if the particle size distribution can be represented reasonably well by a log-normal function. The existing diagram showing the loss rate as a function only of the particle size was expanded to include the polydispersity effects. Experimental measurements of particle wall loss rate were performed by observing the time-dependent changes in particle number concentration for various stirring intensities in a cylindrical stirred chamber. It was shown that by correcting for the polydispersity effect, the dependence of the wall loss rate on particle size and stirring intensity agreed with the theory of Crump and Seinfeld (1981).

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A surface-discharge microplasma device (SMD) was developed for the decomposition of volatile organic compounds (VOCs) in the gas phase. The device is composed of a microscale-patterned electrode, a dielectric substrate, and a ground electrode. As a result of localized dielectric barrier discharge (DBD), surface-discharge microplasma was generated when a piezoelectric-transformed high voltage (66.7 kHz, 3.5 kV) was applied to the microscale-patterned electrode. The discharge current and voltage characteristics of the DBD were analyzed under atmospheric conditions. Toluene decomposition rate was evaluated by gas chromatography–mass spectrometry and nondispersive IR-absorption CO2 analysis. A decomposition efficiency of more than 99% was achieved in batch experiments. When the SMD was operated in a flow reactor, 30–80% of toluene was reduced with the percentage depending on residence time. The carbon balance between the toluene starting material and the CO2 product indicates that toluene was almost completely decomposed into CO2 by atomic oxygen in the microplasma.