Emission factors of air toxics from semiconductor manufacturing in Korea

The development of local, accurate emission factors is very important for the estimation of reliable national emissions and air quality management. For that, this study is performed for pollutants released to the atmosphere with source-specific emission tests from the semiconductor manufacturing industry. The semiconductor manufacturing industry is one of the major sources of air toxics or hazardous air pollutants (HAPs); thus, understanding the emission characteristics of the emission source is a very important factor in the development of a control strategy. However, in Korea, there is a general lack of information available on air emissions from the semiconductor industry. The major emission sources of air toxics examined from the semiconductor manufacturing industry were wet chemical stations, coating applications, gaseous operations, photolithography, and miscellaneous devices in the wafer fabrication and semiconductor packaging processes. In this study, analyses of emission characteristics, and the estimations of emission data and factors for air toxics, such as acids, bases, heavy metals, and volatile organic compounds from the semiconductor manufacturing process have been performed. The concentration of hydrogen chloride from the packaging process was the highest among all of the processes. In addition, the emission factor of total volatile organic compounds (TVOCs) for the packaging process was higher than that of the wafer fabrication process. Emission factors estimated in this study were compared with those of Taiwan for evaluation, and they were found to be of similar level in the case of TVOCs and fluorine compounds.     

Development of a hybrid microbial fuel cell (MFC) and fuel cell (FC) system for improved cathodic efficiency and sustainability: the M2FC reactor

In an effort to improve the efficiency and sustainability of microbial fuel cell (MFC) technology, a novel MFC reactor, the M2FC, was constructed by combining a ferric-based MFC with a ferrous-based fuel cell (FC). In this M2FC reactor, ferric ion, the catholyte in the MFC component, is regenerated by the FC system with the generation of additional electricity. When the MFC component was operated separately, the electricity generation was maintained for only 98 h due to the depletion of ferric ion in the catholyte. In combination with the fuel cell, however, the production of power was sustained because ferric ion was continually replenished from ferrous ion in the FC component. Moreover, the regeneration process of ferric ion by the FC produced additional energy. The M2FC reactor yielded a power density of up to 2 W m⁻² (or time-averaged value of approximately 650 mW m⁻²), density up to 20 times (or approximately six times based on time-averaged value) higher than the corresponding MFC system.     

Stabilization and solidification of elemental mercury for safe disposal and/or long-term storage

A simple and highly effective stabilization/solidification (S/S) technology of elemental mercury using only sulfur with paraffin is introduced. First, elemental mercury is mixed with an excess of sulfur powder and heated to 60 degrees C for 30 min until elemental mercury is converted into mercuric sulfide (HgS black, metacinnabar) (Step 1). Then, metacinnabar with additional sulfur is poured into liquid paraffin (Step 2). Finally, the mixture is melted at 140 degrees C and settles to the bottom of the vessel where it cools and solidifies under the layer of liquid paraffin (Step 3). The proposed S/S method with sodium sulfide nonahydrate (Na2S x 9H2O) as an additive is also tested for comparison. The average toxicity characteristic leaching procedure test values are 6.72 microg/L (no additive) and 3.18 microg/L (with additive). Theses concentrations are well below the Universal Treatment Standard (25 microg/L). Effective diffusion coefficient evaluated from accelerated leach test and average headspace concentration of Hg vapor after 18 hr are 3.62 x 10(-15) cm2/sec, 0.55 mg/m3 (no additive) and 5.86 x 10(-13) cm2/sec, 0.25 mg/m3 (with additive).     

Distribution of polycyclic aromatic hydrocarbons in agricultural soils in South Korea

The content and type of polycyclic aromatic hydrocarbons (PAH) in soils from paddy fields and upland areas in South Korea were determined using gas chromatography linked to mass spectrometry (GC–MS). The distribution map of total PAH content was obtained as a contour plot using a geographical information system. The overall distribution of PAH was found to be closely related to the pollution sources, the size of city and the type of industry. The average content of total PAH in all samples was 236 μg kg⁻¹, and the range was from 23.3 to 2834 μg kg⁻¹. The highest concentrations were found in soils sampled near iron processing plants. The concentration of PAH decreased in the order fluoroanthene>benzo(b)fluoroanthene>pyrene. Special PAH compound ratios, such as phenanthrene/anthracene and fluoroanthene/pyrene, were calculated to evaluate the origin. The collected data suggested that the pyrogenic origins such as motor vehicle exhaust and heavy industry emission were the dominant source of PAH in Korean soils.     

Photocatalytic oxidation of gas-phase elemental mercury by nanotitanosilicate fibers

Photocatalytic fibers were generated from the continuous evaporation of titanium tetraisopropoxide with tetraethyl orthosilicate through a flame burner. The morphology, the crystal form, and the components of the nanotitanosilicate fibers were analyzed by Raman spectroscopy, Field emission-scanning electron microscope, X-ray diffraction, and Brunauer-Emmett-Teller surface area analysis. The nanotitanosilicates prepared by three different carrier gases (air, N(2), and Ar) were tested for their photocatalytic ability to remove/oxidize gas-phase elemental mercury. Under UV black light, the Hg(0) capture efficiencies were 78%, 86%, and 85% for air, N(2), and Ar, respectively. For air, the value was close to 90%, even under household fluorescent light. The Hg(0) capture efficiency by nanotitanosilcate was measured under fluorescent light, UV black light, and sunlight.     

Gas-phase elemental mercury removal in a simulated combustion flue gas using TiO2 with fluorescent light

A previously proposed technology incorporating TiO₂ into common household fluorescent lighting was further tested for its Hg⁰ removal capability in a simulated flue-gas system. The flue gas is simulated by the addition of O₂, SO₂, HCl, NO, H₂O, and Hg⁰, which are frequently found in combustion facilities such as waste incinerators and coal-fired power plants. In the O₂ + N₂ + Hg⁰ environment, a Hg⁰ removal efficiency (η_Hg) greater than 95% was achieved. Despite the tendency for η_Hg to decrease with increasing SO₂ and HCl, no significant drop was observed at the tested level (SO₂: 5–300 ppm_v, HCl: 30–120 ppm_v). In terms of NO and moisture, a significant negative effect on η_Hg was observed for both factors. NO eliminated the OH radical on the TiO₂ surface, whereas water vapor caused either the occupation of active sites available to Hg⁰ or the reduction of Hg₀ by free electron. However, the negative effect of NO was minimized (η_Hg > 90%) by increasing the residence time in the photochemical reactor. The moisture effect can be avoided by installing a water trap before the flue gas enters the Hg⁰ removal system.

Implications: This paper reports a novel technology for a removal of gas-phase elemental mercury (Hg⁰) from a simulated flue gas using TiO₂-coated glass beads under a low-cost, easily maintainable household fluorescent light instead of ultraviolet (UV) light. In this study, the effects of individual chemical species (O₂, SO₂, HCl, NO, and water vapor) on the performance of the proposed technology for Hg⁰ removal are investigated. The result suggests that the proposed technology can be highly effective, even in real combustion environments such as waste incinerators and coal-fired power plants.     

Emission Factors of Air Toxics from Semiconductor Manufacturing in Korea

Abstract

The development of local, accurate emission factors is very important for the estimation of reliable national emissions and air quality management. For that, this study is performed for pollutants released to the atmosphere with source-specific emission tests from the semiconductor manufacturing industry. The semiconductor manufacturing industry is one of the major sources of air toxics or hazardous air pollutants (HAPs); thus, understanding the emission characteristics of the emission source is a very important factor in the development of a control strategy. However, in Korea, there is a general lack of information available on air emissions from the semiconductor industry. The major emission sources of air toxics examined from the semiconductor manufacturing industry were wet chemical stations, coating applications, gaseous operations, photolithography, and miscellaneous devices in the wafer fabrication and semiconductor packaging processes. In this study, analyses of emission characteristics, and the estimations of emission data and factors for air toxics, such as acids, bases, heavy metals, and volatile organic compounds from the semiconductor manufacturing process have been performed. The concentration of hydrogen chloride from the packaging process was the highest among all of the processes. In addition, the emission factor of total volatile organic compounds (TVOCs) for the packaging process was higher than that of the wafer fabrication process. Emission factors estimated in this study were compared with those of Taiwan for evaluation, and they were found to be of similar level in the case of TVOCs and fluorine compounds.     

Occurrence of disinfection by-products in tap water distribution systems and their associated health risk

The concentrations of trihalomethanes (THMs), including chloroform, bromodichloromethane, dibromochloromethane, and bromoform, and haloacetic acids (HAAs; monochloroacetic acid, monobromoacetic acid, dibromoacetic acid, dichloroacetic acid, and trichloroacetic acid) were measured in tap waters passing through water distribution systems of six water treatment plants in Seoul, Korea, and their associated health risks from exposure to THMs through ingestion, dermal contact, and inhalation were estimated using a probabilistic approach. The concentration ranges for total THMs and HAA₅ were 3.9–53.5 and <LOD–49.5 μg/L, respectively. Among DBPs, chloroform, bromodichloromethane, dichloroacetic acid, and trichloroacetic acid were the most frequently detected. Spatial and seasonal variations in concentrations of THMs and HAAs in the six water distribution systems were significant (P?<?0.001).The mean lifetime cancer risks through ingestion, dermal contact, and inhalation during showering ranged as 7.23–10.06?×?10^?6, 2.19–3.63?×?10^?6, and 5.22–7.35?×?10^?5, respectively. The major exposure route to THMs was inhalation during showering. Sensitivity analysis showed that shower time and shower frequency had a great impact on the lifetime cancer risk by the exposure to THMs in tap water.     

Effect of preparation method of noble metal supported catalyts on formaldehyde oxidation at room temperature: Gas or liquid phase reduction

Formaldehyde (HCHO) is toxic to the human body and is one of the main threats to the indoor air quality (IAQ). As such, the removal of HCHO is imperative to improving the IAQ, whereby the most useful method to effectively remove HCHO at room temperature is catalytic oxidation. This review discusses catalysts for HCHO room-temperature oxidation, which are categorized according to their preparation methods, i.e., gas-phase reduction and liquid-phase reduction methods. The HCHO oxidation performances, structural features, and reaction mechanisms of the different catalysts are discussed, and directions for future research on catalytic oxidation are reviewed.     

Above- and belowground interactions drive habitat segregation between two cryptic species of tropical trees

In the lowlands of central Panama, the Neotropical pioneer tree Trema micrantha (sensu lato) exists as two cryptic species: "landslide" Trema is restricted to landslides and road embankments, while "gap" Trema occurs mostly in treefall gaps. In this study, we explored the relative contributions of biotic interactions and physical factors to habitat segregation in T. micrantha. Field surveys showed that soils from landslides were significantly richer in available phosphorus and harbored distinct arbuscular mycorrhizal fungal (AMF) communities compared to gap soils. Greenhouse experiments designed to determine the effect of these abiotic and biotic differences showed that: (1) both landslide and gap species performed better in sterilized soil from their own habitat, (2) the availability of phosphorus and nitrogen was limiting in gap and landslide soils, respectively, (3) a standardized AMF inoculum increased performance of both species, but primarily on gap soils, and (4) landslide and gap species performed better when sterilized soils were inoculated with the microbial inoculum from their own habitat. A field experiment confirmed that survival and growth of each species was highest in its corresponding habitat. This experiment also showed that browsing damage significantly decreased survival of gap Trema on landslides. We conclude that belowground interactions with soil microbes and aboveground interactions with herbivores contribute in fundamental ways to processes that may promote and reinforce adaptive speciation.