• Journal of Korean Society for Atmospheric Environment
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• v.22 no.2
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• pp.259-266
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• 2006

A dual-channel glass coil sampling technique was used to measure hourly formaldehyde concentration in the ambient air. The dual-channel coil sampling assembly consists of three parts; an all-pyrex 28-turn coil made of 0.2-cm internal diameter glass tubing for gas-liquid contact and scrubbing of soluble gases, an inlet section upstream of the coil for introducing sample air and scrubbing solution, and a widened glass section downstream of the coil for gas-liquid separation. The scrubbing solution used was a dilute aqueous DNPH (dinitrophenylhydrazine) solution. Hourly concentration of formaldehyde was determined at a Gwangju semi-urban site during two intensive studies between September and October using the dual channel glass-coil/DNPH sampling technique and HPLC (High Performance Liquid Chromatography) analysis. The mean concentration was 1.7($0.4{\sim}4.7$) and 3.0($0.5{\sim}19.1$) ppbv for the September and October intensives, respectively, which are considerably low, compared to those measured in polluted urban areas around the world including several urban areas of Korea. The diurnal variation showed significant increase of formaldehyde in the daytime suggesting the dominance of formation of formaldehyde due to photochemical oxidation of methane and other hydrocarbons. An increase in the formaldehyde sometimes in the night might be due to an increase in primary source, i.e. traffic emissions. It was also found that rapid increase in formaldehyde levels from 3.0 to 19.1 ppbv in the afternoon on October 20 was due to plumes from burning of agricultural wastes such as rice straw and stubble. It is expected from the measurement data that the constructed dual-channel glass coil sampling system can be utilized for measuring atmospheric concentration of the formaldehyde with high time resolution.

• Water for future
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• v.15 no.2
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• pp.11-22
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• 1982

This study is to find out the reasonable drainage system of sewerage in connection with the geographical conditions, the form of city, and the problem of sewerage in and around Seoul. (1) In supplying the sewerage sewer, the separating system is desirable in connection with the problem of sewerage disposal in future. However, in the existing urban district, the conjunction system is used because of the large amount invested according to the diversion of the sewer of the separation system and the influence of the traffic communication. The sewer of the separating system should be used in the case of the fundamental reconstruction of structure as the redevelopment of the urban district or the subway and new-development of area. Therefore, the separating system should be used completely until the goal year. (2) Drainage area was divided for the natural flowing, considering that the 38 streams and topography paly a role of the main stream of drainage. There are the branches, Guyui, Dug-island, Jayang, Hannam, Banpo, Amsa whose divisions are impossible. In these branches, the drain planning was suggested a forced control method by using the exiting pond age and the pumping station. (3) The best available method which improbes the water quality in Han river is as follows. The sewerage is catched and carried to the sewerage disposal plant by establishing the intercept sewer in both or one side of stream. At the same time, the groudwater volume which springs in each stream is drained separatively.

• International Journal of Highway Engineering
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• v.20 no.1
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• pp.69-76
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• 2018

PURPOSES : This study determined the optimal usage rate of RAP (reclaimed asphalt pavement) using cold central-plant recycling (CCPR) on a road-surface layer. In addition, a mixture-aggregate gradation design and a curing method based on the proposed rate for the surface-layer mix design were proposed. METHODS : First, current research trends were investigated by analyzing the optimum moisture content, mix design, and quality standards for surface layers in Korea and abroad. To analyze the aggregate characteristics of the RAP, its aggregate-size characteristics were analyzed through the combustion asphalt content test and the aggregate sieve analysis test. Moreover, aggregate-segregation experiments were performed to examine the possibility of RAP aggregate segregation from field compaction and vehicle traffic. After confirming the RAP quality standards, coarse aggregate and fine aggregate, aggregate-gradation design and quality tests were conducted for mixtures with 40% and 50% RAP usage. The optimum moisture content of the surface-layer mixture containing RAP was tested, as was the evapotranspiration effect on the surface-layer mixture of the optimum moisture content. RESULTS : After analyzing the RAP recycled aggregate size and extraction aggregate size, 13-8mm aggregate was found to be mostly 8mm aggregate after combustion. After using surface-chipping and mixing methods to examine the possibility of RAP aggregate segregation, it was found that the mixing method contributed very little for 3.32%, and because the surface-chipping method applied compaction energy directly as the maximum assumption the separation ratio was 15.46%. However, the composite aggregate gradation did not change. Using a 40% RAP aggregate rate on the surface-layer mixture for cold central-plant recycling satisfied the Abroad quality standard. The optimum moisture content of the surface-layer mixture was found to be 7.9% using the modified Marshall compaction test. It was found that the mixture was over 90% cured after curing at $60^{\circ}C$ for two days. CONCLUSIONS : To use the cold central-plant recycling mixture on a road-surface layer, a mixture-aggregate gradation design was proposed as the RAP recycled aggregate size without considering aggregate segregation, and the RAP optimal usage rate was 40%. In addition, the modified Marshall compaction test was used to determine the optimum moisture content as a mix-design parameter, and the curing method was adapted using the method recommended by Asphalt Recycling & Reclaiming Association (ARRA).

• Journal of Korean Elementary Science Education
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• v.35 no.1
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• pp.26-38
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• 2016

The purpose of this study was to grasp the characteristics of composition regarding the material-centered integrated unit of environmental and natural studies, a science subject in Finland, to investigate a need for applying the material-centered integrated unit to the science curriculum of Korea. For the purpose, the study made an analysis on contents, inquiry activities, and visual materials (the most important in the elementary science curriculum and textbook composition), and it brought following results: First, as a result of analyzing the area of contents, the bicycle material-centered integrated unit comprised a large proportion of 44 pages (25.3%) of the whole 174 pages from the environmental and natural studies textbook for the third grade. The contents included such various concepts as traffic rules, safety, environmental protection and pollution, recycling and separate collection, tubes and triangular structures, wedges and screws, leverage, wheels, axles, gears, elasticity (spring), friction, and so on. Second, as a result of analyzing contents related to the thinking ability of inquiry activities, "expecting or confirming expectations" and "application" are included in every lesson, and one lesson is composed in such a way that students can study on bicycles as a practical material for their daily life and they can improve various thinking abilities. Third, as a result of analyzing the circumstances of inquiry activities, daily circumstances made up eight lessons (80.0%) and technical and social circumstances made up two lessons (20.0%) by focusing on bicycles, a material related to students' daily life. Fourth, as a result of analyzing visual materials, the percentage of pictures and photos was high at 53.4% and 45.2% respectively. As a result of analyzing the role of visual materials, the percentage of the illustrative role and explanatory-complementary role was high at 52.1% and 47.9% respectively. Lastly, as a result of analyzing from the epistemological view to interpret the relation between visual materials and students and the position of visual materials, the visual textbook materials were provided toward a way that students can decrease their feeling of epistemological separation in the three fields of ideational metafunction, interpersonal metafunction, and textual metafunction.