Byeong-Kyu Lee

Determining contamination level of heavy metals in road dust from busy traffic areas with different characteristics

This study identified the levels and sources of heavy metal contamination in road dust from busy traffic areas in a typical industrial city in Korea. This study compared the total concentrations, as determined by aqua regia digestions and atomic absorption spectroscopy, of cadmium (Cd), copper (Cu), lead (Pb), zinc (Zn) and nickel (Ni) in the road dust from areas with different characteristics such as traffic rotaries, downtown areas, circulation roads, and asphalt and concrete highways. The contamination levels of the heavy metals in the road dust were evaluated using the contamination factor and the degree of contamination. The contamination levels of the heavy metals in the road dust were highly dependent on traffic volume and atmospheric dispersion from traffic rotaries. Industrial emissions and the frequency of brake use and vehicles coming to a complete stop were additional factors that affected the contamination levels in downtown areas. The concrete highway had higher contamination levels of the heavy metals than the asphalt highway. Vehicle speed was also a strong contributing factor to the degree of contamination of heavy metals in the road dust from the circulation roads and highways.

Characteristics, toxicity, and source apportionment of polycylic aromatic hydrocarbons (PAHs) in road dust of Ulsan, Korea

This study identified concentrations, molecular distributions, toxicities, and sources of polycylic aromatic hydrocarbons (PAHs) in road dust from different areas of Ulsan, the largest industrial city in Korea. The total PAH concentrations in industrial areas were dependent on industrial emissions and vehicular exhaust, while those in urban areas were mainly dependent on traffic density, sampling site location, and accumulation of pollutants or road dust. The PAH concentration of each particle size group increased with decreasing particle size. This may be because of the higher surface area available for deposition or coating of PAHs in road dust with smaller particle sizes. The molecular distributions of PAHs among the sites in the petrochemical area and heavy traffic area were similar because of the similarities in their emission sources. The toxic equivalent concentrations (TEQs) of PAHs in the road dust ranged from 0.93 microg/g to 16.74 microg/g in industrial areas and from 4.37 microg/g to 68.84 microg/g in urban areas. The correlation coefficient of total PAH concentration and TEQ in urban areas was 0.98, which was much higher than that in industrial areas where it was 0.75. Principal component analysis showed that PAHs in road dust from Ulsan originate from four main sources: diesel vehicular emissions, oil combustion, gasoline vehicular emissions, and coal combustion.

Analyses of the recycling potential of medical plastic wastes

This study analyzed the recycling potential of plastic wastes generated by health care facilities. For this study, we obtained waste streams and recycling data from five typical city hospitals and medical centers and three animal hospitals in Massachusetts. We analyzed the sources, disposal costs and plastic content of medical wastes, and also determined the components, sources, types and amounts of medical plastic wastes. We then evaluated the recycling potential of plastic wastes produced by general city hospital departments, such as cafeterias, operating rooms, laboratories, emergency rooms, ambulance service and facilities, and animal hospitals. Facilities, laboratories, operating rooms, and cafeterias were identified as major sources of plastic wastes generated by hospitals. It was determined that the recycling potential of plastics generated in hospital cafeterias was much greater than that in other departments. This was mainly due to a very slight chance of contamination or infection and simplification of purchasing plastic components. Finally, we discuss methods to increase the recycling of medical plastic wastes. This study suggests that a classification at waste generating sources, depending upon infection chance and/or plastic component, could be a method for the improved recycling of plastic wastes in hospitals.

Effects of road characteristics on distribution and toxicity of polycyclic aromatic hydrocarbons in urban road dust of Ulsan, Korea

Comparisons between concentration, size effect, molecular distribution, and toxicity of polycyclic aromatic hydrocarbons (PAHs) in urban road dust of Ulsan, Korea, were carried out. The road dust was collected at eleven representative urban sites offering unique road characteristics. The road dust was separated into four size categories as follows: 850-2000 microm, 180-850 microm, 75-180 microm and less than 75 microm. PAHs in the categorized road dust were ultrasonically extracted by a mixture of dichloromethane and n-hexane (1:1) for 30 min. Sixteen PAHs were specifically identified by a high performance liquid chromatography method. Pavement type, traffic volume, vehicle speed and surrounding environment of the study roads greatly affected the overall PAH road dust concentration. The molecular distribution of PAHs was strongly affected by vehicle type, surrounding area and pavement type of road. When the road dust particle size decreased, the total concentration of PAHs increased. The existence of coarse asphalt particles due to the abrasion of new asphalt pavement at some sites could increase the total PAH concentration to a size of 180-850 microm. PAHs in road dust were also evaluated for toxicity using the reported toxicity equivalency factors. The toxicity of PAHs in road dust showed a strong correlation to the total PAH concentration (r(2)=0.955). However, the coefficients of determination (r(2)) for the sizes of 850-2000 microm, 180-850 microm, 75-180 microm and less than 75 microm were 0.966, 0.998, 0.707 and 0.514, respectively.

Assessment of carcinogenic risk due to inhalation of polycyclic aromatic hydrocarbons in PM10 from an industrial city: A Korean case-study

This study investigated the effects of meteorological conditions and spatial variations on the toxicity of polycyclic aromatic hydrocarbons (PAHs) in airborne PM(10) in Ulsan, the largest industrial city in Korea. Daily PM(10) samples were collected on quartz microfiber filters using high volume samplers located in a downtown area, a residential area and an industrial area of Ulsan during spring and summer sampling periods. Sixteen individual PAHs were extracted into a mixture solution of dichloromethane and n-hexane (1:1, v/v) in an ultrasonic bath and were analyzed using a high performance liquid chromatography system with an ultra-violet detector (HPLC-UVD). The average total PAH concentrations from the three representative sampling sites of Ulsan ranged from 16.15 to 57.12 ng/m(3) in spring and from 11.11 to 34.56 ng/m(3) in summer. The toxicity equivalent concentrations (TEQs) of the PAHs in PM(10) of Ulsan ranged from 1.82 to 13.1 ng/m(3), with an average level of 4.17 ng/m(3). The highest TEQs were found in the downtown area, which had an average value of 6.30 ng/m(3) in spring and 5.52 ng/m(3) in summer. BaP and DahA were identified as the major carcinogenic PAHs that contributed to 34.8 and 59.4% of the total carcinogenic potency of PAHs in PM(10) in Ulsan. The identified TEQs were highly correlated (r(2) = 0.73-0.90, p<0.01) with the total PAH concentrations for each area. The TEQs showed a significant correlation (p < 0.01) with the concentration of air pollutants, including PM(10), PM(2.5) and NO(2).

Feasibility of Silver Doped TiO2/Glass Fiber Photocatalyst under Visible Irradiation as an Indoor Air Germicide

This study investigated the feasibility of using Ag-TiO2 photocatalyst supported on glass fiber (Ag-TiO2/GF) prepared by a sol-gel method as an indoor air germicide. An experimental model was designed to investigate the bacterial disinfection efficiency of Staphylococcus (Staph), the most popular bacterium in hospitals in Korea, by the Ag-TiO2/GF photocatalyst. The silver content in Ag/TiO2 was altered from 1 to 10% to investigate the optimal ratio of Ag doped on TiO2/glass fiber (TiO2/GF) for photocatalytic disinfection of Staph. This study confirmed that Ag in Ag-TiO2/GF could work as an electron sink or donor to increase photocatalytic activity and promote the charge separation of electron-hole pairs generated from TiO2 after photon absorption. Ag also acts as an intermediate agent for the transfer of photo-generated electrons from the valence band of TiO2 to an acceptor (O2 gas) to promote photo-oxidation processes. The photocatalytic disinfection activity of Ag-TiO2/GF under visible light increased with the increase in silver content up to 7.5% and then slightly decreased with further increasing silver content. The highest disinfection efficiency and disinfection capacity of Staph using 7.5% Ag-TiO2/GF were 75.23% and 20 (CFU∙s−1∙cm−2) respectively. The medium level of humidity of 60% ± 5% showed better photocatalytic disinfection than the lower (40% ± 5%) or higher (80% ± 5%) levels.

Novel and facile synthesis of Ba-doped BiFeO3 nanoparticles and enhancement of their magnetic and photocatalytic activities for complete degradation of benzene in aqueous solution.

In this work, Bi1-x Bax FeO3 (x=0.05, 0.1 and 0.2mol%) multiferroic materials as visible-light photocatalysts were successfully synthesized via a simple and rapid sol-gel method, at a low temperature and with rapid calcination. Ba loading brought about a distorted structure of BiFeO3 magnetic nanoparticles (BFO MNPs) consisting of small, randomly oriented and non-uniform grains, leading to increased surface area and improved magnetic and photocatalytic activities. Doping of Ba(2+) into pure BFO (Bi1-x Bax FeO3, x=0.2mol%) greatly increased magnetic saturation to 3.0emu/g and significantly decreased the band-gap energy to 1.79eV, as compared to 2.1emu/g and 2.1eV, respectively, for pure BFO. Bi1-xBa xFeO3 of x=0.2mol% exhibited the greatest photocatalytic degradation effect after 60min of visible light irradiation, and reached 97% benzene removal efficiency, leading to production of a high concentration of carbon dioxide (CO2), with 93% and 82% reductions in chemical oxygen demand (COD) and total organic carbon (TOC), respectively. The identified major intermediate products of photodegradation enabled prediction of the proposed benzene degradation pathway. The enhanced photocatalytic activity of benzene removal is due to both mechanisms, photocatalytic and photo-Fenton catalytic degradation.

Effects of Ag doping on the photocatalytic disinfection of E. coli in bioaerosol by Ag–TiO2/GF under visible light

Ag doped TiO2/glass fibers (Ag-TiO2/GF) were prepared and used for photocatalytic disinfection of Escherichia coli (E. coli) in an indoor air environment. The prepared photocatalysts were characterized using scanning electron microscope (SEM) for morphology, X-ray diffraction (XRD) for microstructure, UV-Visible diffuse reflectance spectra (DRS) for optical properties and X-ray photoelectron spectroscopy (XPS) to determine elemental state. The optimized weight fraction of TiO2 in the TiO2/glass fiber (TiO2/GF) was 3%. The silver content in Ag/TiO2 was altered from 1% to 10% to investigate the optimal ratio of Ag doped on the TiO2/GF for the photocatalytic disinfection of E. coli. Doped Ag enhanced the electron-hole separation as well as charge transfer efficiency between the valance band and the conduction band of TiO2. The generated electron-hole pairs reacted with water and molecular oxygen to form strong oxidative radicals, which participated in the oxidation of organic components of E. coli, resulting in bacterial death. The photocatalytic disinfection activity under visible light increased with the increase in silver content up to 7.5% and then decreased slightly with further increasing Ag content. Among the three humidity conditions used in this study (40±5%, 60±5%, 80±5%), the highest disinfection ratio of E. coli by the photocatalytic system was observed in the intermediate humidity level followed by the high humidity level. Using the 7.5% Ag-TiO2/GF and the intermediate level of humidity (60±5%), the highest disinfection ratio and disinfection capacity of E. coli were 93.53% and 26 (CFU/s cm(2)), respectively.

Novel adsorption and photocatalytic oxidation for removal of gaseous toluene by V-doped TiO2/PU under visible light

In this study, V was used as a dopant to defect into the TiO2 lattice, leading to formation of Ti(3+) and V(4+) in the lattice. The presence of Ti(3+) and V(4+) introduced into the TiO2 lattice increased the electron-hole pair generation capacity and electron-hole pair separation efficiency of the TiO2, leading to enhancement of the photocatalytic activity of the photocatalyst. Porous polyurethane (PU) was used to immobilize the V-doped TiO2 by creating chemical bonds. The use of porous substrate contributed to the increased adsorption ability of the enhanced photocatalyst, as well as expanded its application for the removal of toluene from aerosols. Under dark conditions, the V-TiO2/PU only exhibited adsorption ability for toluene treatment in aerosol. Under visible light conditions, the V-TiO2/PU exhibited high photocatalytic oxidation ability for the removal of toluene in aerosol. The photocatalytic oxidation ability was found to depend on the V to TiO2 ratio. The optimal V content in V/TiO2 for enhancing the photocatalytic activity of TiO2 was determined to be 6 wt%. Even under visible light irradiation, the 6% V-TiO2/PU sample could photocatalytically remove 80% of the toluene in 200-ppmV inlet gas, while 89.3% of the removed amount was mineralized into CO2 and H2O.

Dynamics of PM2.5 concentrations in Kathmandu Valley, Nepal

This study analyzed daily patterns and dynamics of PM(2.5) concentrations in the Kathmandu Valley during three winters. The PM(2.5) data showed a daily repetitive cycle which represents influence of local air flow and dispersion and accumulation of air pollutants in the valley. Two concentration peaks were observed in the morning and in the evening periods, and they fell down during the daytime and the nighttime periods. This indicates local emission sources as major contributors in the valley. The more pronounced morning peak compared to the evening peak showed that the upslope wind in the morning helped to move the polluted inversion layer downward, subsequently adding to freshly emitted pollutants and causing a sharp pollutant concentration rise in the morning. Katabatic wind and rise of temperature in the basin during the day helped the pollutant upflow and dilution, resulting in a sharp PM(2.5) concentration decline. Through the afternoon, the decrease in air temperature followed by decrease in wind speed caused to lower PM(2.5) peaks in the evening. Also, higher morning peaks of PM(2.5) concentrations compared to the evening indicated pollution from the previous day is added to the fresh emission. The valley had increased PM(2.5) from the beginning of October which continued till the first week of February. The increase in PM(2.5) peak fit the logistic equation y=[k/(1+exp (p-qx)]+asin(bx) where k, p, q, a, and b are constants.