Development of PM2.5 management strategy in the industrial city of Ulsan : A comprehensive approach to understanding the risk and sources of PM2.5

Sang-Jin Lee Ulsan National Institute of Science and Technology 2024 국내박사

Particulate matter (PM) with an aerodynamic diameter of less than 2.5 μm (PM2.5) is major air pollutants in northeast Asia, with their primary sources being fuel combustion from industrial activity, heating, transportation, and power generation facilities. In addition, gaseous precursors such as sulfur oxides (SOX), nitrogen oxides (NOX), and volatile organic compounds (VOCs) generate secondary aerosols through chemical reactions. The major sources for high PM2.5 events in metropolitan cities are generally local vehicle emissions and secondary formation. Long-range atmospheric transport (LRAT) is also a major reason for high PM events in East Asian megacities such as the Seoul Metropolitan Area, which are frequently influenced by Asian continental outflow. On the other hand, industrial cities are often more strongly influenced by emissions from local industrial activity. The metropolitan city of Ulsan, with a population of 1.13 million, is located in the southeast of the Korean Peninsula. The east coast of Ulsan has a number of petrochemical, nonferrous, automobile, and shipbuilding facilities. Thus, the air quality in Ulsan is greatly influenced by the emissions of various air pollutants from these industrial complexes. However, studies on investigations of PM2.5 pollution in Ulsan have been limited, and there is a need to address the health of residents in an industrial city facing air pollution issues. In this study, we aim to develop comprehensive PM2.5 management strategies by considering source identification, human health assessment, and emission reduction. Currently, episodes of high levels of PM2.5 frequently occur in South Korea as a result of both local emissions and the LRAT of yellow dust and haze events from the Asian continent. Therefore, we investigated the characteristics of PM2.5 pollution episodes semi-continuous measurements obtained from the Yeongnam intensive air quality monitoring station (YN station) in Ulsan. The major source of PM2.5 for the pollution period during winter was LRAT from eastern China and North Korea. The industrial facilities in Ulsan were also responsible for the elevated PM2.5 concentration in winter. The major source of PM2.5 for the pollution period during summer was the local industrial facilities and ship emissions. In addition, secondary formation was enhanced by the air stagnation, high relative humidity, and low PBL height. The influence of thermal power stations and national industrial areas in southern coastal cities was also identified. Moreover, to comprehensively understand the pollution of primary and secondary PM2.5, we developed a technique by combining monitoring and modeling methods to map the spatial distribution of PM2.5. The monitoring data for PM2.5 components and precursors, as well as the air dispersion and receptor modeling data for Ulsan, South Korea were used. It was revealed that the petrochemical and non-ferrous industrial complexes are primary sources of PM2.5 in Ulsan. Similar levels between primary and secondary sulfate were observed, while nitrate concentrations were more influenced by secondary formation rather than primary emissions. Ammonium sulfate concentrations were significantly influenced by industrial activities, while ammonium nitrate concentrations were influenced by both industrial and urban emissions. Significant contributions to SOA formation were observed from the automobile, shipbuilding, and petrochemical industrial complexes, with aromatic compounds such as BTEX playing a significant role. Based on these findings, optimized strategies for managing PM2.5 were proposed for urban areas in individual districts and industrial complexes in Ulsan. However, it should be noted that the estimated concentration of SOA may be underestimated due to the limited number of analyzed VOC species. Particulate matter (PM) contains hazardous air pollutants (HAPs) that may adversely affect human health. In particular, residents living in an industrial city are seriously concerned about the health risks associated with major drivers of cancer risk, such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Therefore, in this study, a novel index called the comprehensive air-risk index (CARI) was developed, which represents the human health risks associated with HAPs. Furthermore, to enhance the spatiotemporal resolution of CARI, a machine-learning approach was implemented using measurement data for PAHs and heavy metals. Over the course of eight years, the risk of PAHs decreased, whereas the risk of heavy metals exhibited a different trend in Ulsan. In addition, the trends of PM2.5 concentration and risk can differ in Ulsan. Earlier studies have also documented elevated concentrations of highly toxic heavy metals in PM2.5 in Ulsan. CARI, CAI and AQHI displayed different seasonal patterns. Hence, in large industrial cities, the proportion of HAPs within PM2.5 and meteorological conditions bears greater significance in health risk assessment than the mass concentration of PM2.5. The effectiveness of CARI in reflecting the health risks associated with HAPs in an industrial city can be conclusively affirmed. Utilizing machine learning and the novel risk index, CARI allows for the identification of priority risk areas in an industrial city at high spatio-temporal resolution. While the average CARI was higher in petrochemical and nonferrous industrial areas, it did not surpass the ‘Unhealthy’ threshold of 150, and there were areas that only exceeded the ‘Unhealthy for sensitive groups’ level of 100. In addition, the Onsan and Yaeum districts were identified as high-risk areas, despite having low population density, as they are primarily industrial areas. Finally, to propose the most effective PM2.5 emission reduction policies in Ulsan, machine learning approach was considered based on reduction scenarios. Emission reduction scenarios were simulated for the major components of PM2.5, including SO4 2-, NO3 -, NH4 +, OC, and EC, which contribute significantly to the PM2.5 mass concentration. When the concentrations of five components were uniformly reduced, PM2.5 mass concentration exhibited the most significant decrease in the scenario where OC concentration was reduced. Moreover, 'Bad' days determined by PM2.5 concentration (exceed 35 µg/m3) also showed the greatest decreased in the scenario with decreased OC concentration. SO2 and meteorological conditions were found to be the main factors for CARI related to human health risks caused by HAPs. In addition to SO2, NH4 +, OC, and EC showed high importance. When simulating the concentration reduction scenarios for these four components, the CARI decreased the most when the SO2 concentration was reduced. Moreover, 'Unhealthy' days determined by CARI (exceed 150) also showed the greatest decreased in the scenario with decreased SO2 concentration. This means that SO2 emission should be prioritized for control to reduce the risk of PM2.5. In conclusion, OC-related (i.e. VOCs) emissions should be controlled to efficiently reduce PM2.5 mass concentration, and SO2-related emissions (i.e. industrial activity) should be controlled to reduce human health risk. These studies provide basic information for improving air quality and will benefit the residents of Ulsan. It can also be applied to other major cities around the world to help improve global air quality.

Long-range atmospheric transport of PM2.5 and its components in Ulsan, South Korea : chemical characterization, source identification, and nontarget screening

Ho-Young Lee Ulsan National Institute of Science and Technology 2025 국내박사

Spatial-temporal variations and source identification of volatile organic compounds and their potential for O3 and SOA formation in the urban and industrial areas

Seong-Joon Kim Ulsan National Institute of Science and Technology 2021 국내박사

Volatile organic compounds (VOCs) have a critical impact on human health and the environment, and they are commonly emitted from a variety of sources, such as anthropogenic and biogenic sources. Also, VOCs are currently a big headache in the world due to their secondary formation for ozone (O3) and secondary organic aerosol (SOA) in the atmosphere. Seoul, one of the largest cities in Northeast Asia, is the capital city of South Korea with 9.8 million inhabitants and 3.1 million vehicles, and Ulsan located in the southeast of the Korean Peninsula with 1.1 million inhabitants is the largest industrial city, including automobile, heavy-shipbuilding, petrochemical, and non-ferrous industrial complexes in South Korea. Therefore, Seoul and Ulsan could have a significant impact on the VOC pollution from human (e.g., gasoline/diesel vehicular exhausts and printing/painting solvents) and industrial activities (e.g., solvent usage and production/combustion processes). Nevertheless, studies on the atmospheric VOCs and their potential for the O3 and SOA formation have been rarely conducted from now on. The integrated monitoring of atmospheric VOCs in this study was divided into (1) primary monitoring of VOCs in the urban city using passive air samplers (PASs), (2) subsequent monitoring of VOCs in the urban city using an active air sampler (AAS), and (3) simultaneous monitoring of air pollutants in the industrial city using the PAS. Finally, the implication for the control strategy of VOCs, SOA, and O3 was suggested. In the primary monitoring, PASs were seasonally deployed to measure 50 VOCs at 26 urban, 4 road, and 6 background sites in Seoul. Among the target compounds, toluene (summer: 8.72 μg/m3; winter: 5.47 μg/m3), ethyl acetate (summer: 2.36 μg/m3; winter: 3.51 μg/m3), and ethylbenzene (summer: 1.72 μg/m3; winter: 0.88 μg/m3) exhibited higher mean concentrations than other compounds. Printing offices and industrial facilities seem to have strong influences on the VOC levels in the center and southwest of Seoul, respectively. Diagnostic ratios indicated that the main sources of VOCs were related to local volatilization in summer and vehicular exhaust and transport from other areas in winter. Positive matrix factorization (PMF) suggested four major sources of VOCs: residential/commercial solvents for printing and painting (Factor 1); transport from other areas (Factor 2); industrial solvents for painting, manufacturing, and cleaning (Factor 3); and gasoline/diesel vehicular exhausts (Factor 4). Factors 1 and 3 were dominant in summer, and Factors 2 and 4 were dominant in winter. In conclusion, the seasonal meteorological conditions (e.g., temperature and wind patterns) were found to play an important role in the spatial distribution of VOCs in Seoul, and solvent use was a predominant source. In the subsequent monitoring, a sequential tube sampler (STS-25) was used to automatically collect 24 air samples for a day every month at an urban site in Seoul. The annual mean concentration of toluene (9.08 ± 8.99 μg/m3) was the highest, followed by ethyl acetate (5.55 ± 9.09 μg/m3), m,p-xylenes (2.79 ± 4.57 μg/m3), benzene (2.37 ± 1.55 μg/m3), ethylbenzene (1.81 ± 2.27 μg/m3), and o-xylene (0.91 ± 1.47 μg/m3), indicating that they accounted for 77.8–85.6% in four seasons. The Σ60 VOC concentrations in spring and winter were statistically higher compared to in summer and fall due to the location of sampling sites/periods, wind patterns, and major sources in the surrounding area. Overall, the concentrations of individual VOCs were higher during the time in the presence of sunlight than at late night and dawn due to human activities. From conditional bivariate probability function (CBPF) and concentration weighted trajectory (CWT) analysis, domestic effects, such as vehicular exhaust and solvents in Seoul seemed to be dominant; however, sometimes higher concentration events of VOCs might occur from China, North Korea, and industrial facilities nearby Seoul. Benzene, toluene, ethylbenzene, m,p,o-xylenes (BTEX) were the most abundant compounds for the secondary organic aerosol formation potential (SOAFP), which accounted for 5–29% of the PM2.5 concentration during the four seasons. The cancer and non-cancer risks for targeted VOCs were the safety level below the tolerable level (1 × 10-4) and the acceptable safe level (Hazard quotient: HQ < 1), respectively in this study area. Although the levels of the risk and the SOAFP for individual VOCs were not severe, human activities inner-Seoul were a predominant source and the transported effect was identified. In the simultaneous monitoring, PASs for VOCs, O3, NO2, and SO2 were deployed during four seasons 2019–2020 at 6 industrial and 10 urban sites in Ulsan. During the whole sampling periods, the concentration of toluene (mean: 8.75 μg/m3) was the highest among 50 VOCs, followed by m,p-xylenes (4.52 μg/m3), ethylbenzene (4.48 μg/m3), 3-methylpentane (4.40 μg/m3), n-octane (4.26 μg/m3). The seasonal variation of total VOC concentration was not statistically different, indicating that a large amount of VOCs is emitted to the atmosphere throughout a year as a characteristic of the industrial city. On the other hand, the concentrations of O3, NO2, and SO2 had a seasonal characteristic due to meteorological conditions and different sources. The spatial distributions of total VOCs, NO2, and SO2 showed that industrial complexes were major sources, while higher concentrations of O3 were observed in the outskirts of the sampling sites. From the PMF model, five major sources (Factor 1: production processes in the petrochemical industries and gasoline/diesel vehicular exhausts; Factor 2: solvent usage in automobile and ship manufacturing; Factor 3: production processes in the petrochemical/non-ferrous industries and ship emission; Factor 4: gasoline evaporation and combustion in the petrochemical/non-ferrous industries; and Factor 5: industrial solvent usage and secondary formation) were identified. Finally, aromatic compounds, such as m,p,o-xylenes, toluene, and 1,2,4-trimethylbenzene were determined as the most reactive compounds for the O3 formation; therefore, decreasing in the emission amount of these species can be more effective than reducing in that of NO2 in terms of the O3 reduction in the case of this study area. In conclusion, in comparison with the main sources between Seoul and Ulsan, the mean contribution of the main sources of VOCs was totally different. As expected, the effects from atmospheric VOCs primarily emitted from industrial activities were substantial in Ulsan, while human activities, such as printing/painting solvents and gasoline/diesel vehicular exhausts were dominant in Seoul. Therefore, different types of reduction strategy in the emission amount of VOCs should be applied according to a characteristic of the cities. Furthermore, three steps of the procedure applied in this study are suggested; (1) Measurement & analysis: level of VOCs and spatial-temporal variations are identified using the PAS and AAS, (2) Main sources: the most important thing is to look for the source origin using several advanced tools, such as diagnostic ratio, CBPF, CWT, and PMF, and (3) Secondary formation: the relationship between VOCs, SOA, and O3 should be revealed. In the future, the emission aspect, composition, reactivity, and concentration of precursors for the SOA and O3 formation, such as VOCs will be continuously changed. Therefore, integrated monitoring for air pollutants should be periodically conducted for the control strategy of VOCs, SOA, and O3, and this study will be helpful for the improvement of air quality. Also, this monitoring approach can be explored in the urbanized and industrialized cities in the world.

Analyzing the Fire Safety and Thermal Performances of the Liquid-Immersion Battery (LImB) Energy Storage System (ESS)

Junho Bae Ulsan National Institute of Science and Technology 2025 국내박사

Lithium-ion batteries (LIBs) are a leading energy storage technology, recognized for their high energy density and outstanding electrochemical performance. They are widely used in electric vehicles (EVs), energy storage systems (ESS), and consumer electronics. However, a significant challenge for LIBs is their susceptibility to thermal runaway, which can lead to fire and explosion. This issue is particularly important in ESS applications where a large number of high-energy cells are concentrated. In these systems, the risk of thermal runaway is affected by heat generation, the presence of combustible materials, and oxygen exposure, so safety is a top priority in all applications. A variety of safety measures have been developed to reduce the risk of fire, such as battery thermal management systems (BTMS), fire extinguishers, and other suppression methods. Existing extinguishment technologies typically rely on oxygen separation or cooling mechanisms to control combustion. Chemicals such as Novec 1230, ABC powders, and phosphoric acid-based compounds are typically used to suppress flames, while cooling systems use liquid nitrogen or refrigerants to reduce battery temperature. However, these solutions only work after a fire has started and are reactive rather than preventive. These systems also struggle to manage the challenges of high-energy systems such as ESS, where slow heat release, excessive suppression, and anaerobic propagation limit their effectiveness. Among the various LIB applications, ESS poses the greatest safety risk due to its high concentration of high-density cells. ESS plays a critical role in grid stabilization and renewable energy integration, but safety concerns have hindered its widespread adoption. For example, South Korea, a leader in ESS deployment, has reported more than 50 fire-related ESS failures, destroying approximately 1 GWh of storage capacity, equivalent to 10% of its total installed capacity. These incidents are concerning because the root cause of the fires remains uncertain, complicating the development of effective countermeasures. Given the limitations of existing fire suppression systems, recent research has explored immersion- based cooling methods that continuously submerge batteries in a coolant. This approach provides immediate heat release and continuous thermal management in the event of thermal runaway. However, practical implementation is hampered by the lack of an appropriate immersion agent that meets safety and performance criteria. Ideally, the immersion agent should be non-corrosive, electrically non-conductive, and have high thermal conductivity and capacity. Unfortunately, most existing solutions are ineffective and incomplete in suppressing fires due to poor heat dissipation. Therefore, immersion-based solutions are primarily used for fire prevention rather than active suppression. Despite these challenges, fire suppression systems play a critical role in large-scale ESS with capacities exceeding 1,000 kWh, while smaller ESS (~10 kWh) commonly used in residential environments often lack adequate fire prevention measures. This gap in safety protocols exacerbates the risks in the rapidly expanding ESS market. To ensure the safe deployment of ESS, next-generation fire prevention and suppression technologies need to go beyond conventional response strategies. Future developments should focus on integrated thermal management solutions that provide both continuous fire prevention and effective suppression to enhance safety in large-scale ESS applications. 1. Battery-in-Fire-Proof Material (BIF) Module To expand the applicability of fire extinguishers, we have developed a system that immerses batteries in a fire-resistant material (BIF) with a hermetic seal to prevent direct exposure to fire extinguishers. In this system, all battery cells are fully immersed in a liquid fire-retardant material (FPM) with high thermal conductivity and heat capacity. This setup allows for immediate fire suppression under extreme conditions while improving electrochemical performance through effective thermal management during normal operation. This study investigates the key components and practical applications of BIF technology. First, the key materials, including fire-retardant and sealing materials, are described in detail and how they are integrated into the BIF cell and module. Second, a method to prevent fire propagation by intentionally overheating a single cell within the BIF module is evaluated and the results are compared to a conventional LIB module. Third, the electrochemical performance of the BIF system is analyzed, including cycle, capacity, EIS, maximum charge rate, and operating temperature under severe conditions. The BIF system overcomes the limitations of conventional post-ignition fire suppression methods and achieves breakthroughs in fire safety and thermal management. By providing both fire prevention and thermal control, BIF technology shows significant potential in the fields of electric mobility (e.g., electric scooters, kickboards), energy storage systems (ESS), and electric vehicles (EVs). 2. LImB (Liquid Immersion Battery) ESS This study evaluates the fire prevention and suppression performance of a liquid-immersed 10kWh ESS battery system compared to a conventional LIB-ESS equipped with a standard fire extinguisher such as ABC powder. In the fire stability test, the conventional LIB-ESS system experienced thermal runaway, which resulted in rapid fire spread and system destruction, with a maximum temperature exceeding 1300°C. In contrast, the liquid-immersed system effectively mitigated the fire risk. The maximum temperature of the abused battery was only 498°C, and the adjacent cells were kept below 50°C, preventing fire spread. The initial fire was extinguished within 2 seconds, significantly reducing the size and speed of the spread. In addition to the fire suppression function, the liquid-immersed system provides improved thermal management during normal operation. Compared with conventional LIBs, it reduces the temperature rise by 6.3 times and reduces the temperature fluctuation between cells from 3.4°C to 1.5°C, ensuring stable and uniform operation. To further evaluate the practical applicability, the liquid-immersed ESS was deployed in an independent power plant and underwent actual operation tests. Despite the increasing demand for small-scale ESS, empirical studies on fire suppression and thermal management are lacking. There are few studies that systematically compare empirical data according to various fire suppression methods in ESS, leaving a gap in the development of standardized operating requirements for ESS safety. This study aims to fill this gap, establish key performance indicators for ESS safety, and contribute to the development of science-based safety guidelines for the popularization of safe and reliable ESS technology.

A Gene-Centric Perspective of Scientific and Technological Innovations

Woochul Jung Ulsan National Institute of Science and Technology 2023 국내석사

유전자와 유전자 산물에 대한 연구는 현대 생명공학의 기초가 되며, 의학, 농업, 식량산업, 에너지 공급, 환경 정화 등 여러 분야로 응용이 가능한 것으로 알려져 있다. 이러한 과학적 발견들과 기술 혁신을 유전자 중심의 관점에서 거시적으로 조사하고자, 본 논문에서는 연구 논문과 특허에 대한 대규모 선별이 진행되었다. 각 유전자가 갖는 과학적 파급력을 보기 위해서 PubMed에서 접근 가능한 연구 논문 중 제목과 초록에 유전자 또는 유전자 산물이 언급된 자료들을 수집하였다. 기술 혁신 부분에 대응하는 자료로는 미국특허청(USPTO)에서 공개된 특허 출판물이 수집되었다. 문헌 자료 선별과 함께, 유럽 생물정보학 연구소에서 관리하는 UniProt 협의체 데이터베이스 중 선별·제공되는 일부 항목들의 유전자-단백질 명칭을 수집하였고, 이는 이후 유전자 간에 지나치게 중복된 명칭이나 두문자어로 인한 혼동을 방지하기 위해 원소가 공유되지 않는 집합들로 일관되게 군집되었다. 결과적으로 제목/초록에 이러한 유전자 항목을 언급한 논문과 특허들의 연도별 수치를 바탕으로 인간 유전체 프로젝트가 시작된 이후의 추세를 보고하였다. 각 유전자 인용 추세는 연구 논문에서와 비교할 때 발명 문헌에서 변동이 더 큰 것으로 보였고, 두 부문 모두 의료 분야에서 유전자 인용에 대한 기여가 두드러졌다. 지금까지 유전자를 인용한 문헌들은 증가 추세였으나 제목이나 초록에 새롭게 언급되는 유전자의 수는 최근들어 감소하였다. 반면, 이미 연구된 유전자들의 새로운 조합들이 활발히 탐구되는 것으로 보이며, 이러한 조합에 자주 포함된 유전자일수록 단순 인용 횟수의 상위권 유전자보다 생명공학의 발전을 잘 설명히는 것으로 보인다. Research on genes and gene products is a foundation of modern biotechnology, and recognized for its applicability in medicine, agriculture, food industry, energy supply, environmental remediation, and many others. To investigate a macroscopic and gene-centric perspective of scientific discoveries and technological innovations, we employed a large-scale curation of research papers and patents. As a raw data to represent the scientific impact of each gene, we collected the entire set of research articles available on PubMed, that have the names of genes or gene products in their title or abstract. The more dedicated literature source, the United States Patent and Trademark Office (USPTO) patent publication, was retrieved as a source data to represent the counterpart in technological innovations. In parallel with this literature curation, the gene symbols were collected from curated subset of UniProt consortium database maintained by European Bioinformatics Institute, and then clustered into the non-overlapping standardized sets to eliminate the overwhelming duplicates and possible contamination by common acronyms. Based on the annual counts of papers or patents whose titles/abstracts include a given gene, we show the overall trends of genetic research since the launch of the Human Genome Project. The gene citation fluctuated more in inventive activity compared to those in the research, while both sides were largely contributed by medicinal discipline. The volume of publications mentioning genes has been increased while the debut of new genes on titles and abstracts has been deflated. In contrast, new combinations of previously-studied genes kept actively explored, and their frequently adopted genes informed biotechnology innovations rather than sheerly top-studied genes.

Measuring Public Life Through Digital Technologies: Investigating the Use of WiFi Sensing for Enhancing Public Space

Juhyeon Park Ulsan National Institute of Science and Technology 2022 국내박사

Vibrant public spaces are an indicator of the high quality of urban life. The success or failure of urban public spaces is dependent on how people use and interact with others in those spaces. Public life researchers have primarily measured the activities and behaviors of users through direct observation methods, reporting on findings that they have witnessed for themselves. Such simple techniques still have their place and are valuable but present their own set of multi-tasking challenges. For example, the researchers may be considering several themes; by nature, this approach is both labor-intensive and time-consuming. However, one digital technology, WiFi sensing, has recently been getting attention as a means for enhancing the research process by overcoming these data collection limitations. It passively detects the presence and location of a person who has a WiFi-enabled device 100 meters away around a WiFi sensor. This thesis investigates the use of WiFi sensing as an alternative observation method for measuring different aspects of public life and public space. Many urban researchers have adopted sensing technology to analyze people’s mobility in various metropolitan areas. However, their findings are also relevant to quantifying people’s number and flow rate on the move. Currently, it seems unlikely that decision-makers will leverage this data to enhance the public space. This gap seems to arise from installing sensors and obtaining basic information without systematically considering how to apply the technology and the benefits to public life. These limitations align with the critical view of smart cities; sensing technology cannot transform the urban paradigm by offering new insights without moving beyond the restrictions of traditional approaches. The feasibility of WiFi sensing is explored in a series of analyses regarding (1) the spatial and temporal properties representing people’s movements and behavior, (2) the possibilities of measuring alternative key metrics of public life, and (3) the practical applications for urban planning and design. Before presenting the findings, I proposed a conceptual framework that leverages the WiFi sensing and the public life survey framework, highlighting how the two fields are associated. I conducted several data-gathering experiments for the analyses, including WiFi and ground truth data using GPS. I then assessed the properties of WiFi data focusing on the spatial accuracy to positioning people’s location. Next, I tested stay point detection from WiFi traces and examined the accuracy of the WiFi stay points with GPS stay points as ground truth. The thesis discusses the findings concerning the possibilities of WiFi sensing for public life studies in the context of a series of guided questions. First, based on our WiFi sensor network with an average sensor spacing of 50 meters, the WiFi data provides an approximate location of people within 20-30 meters accuracy at an interval of 30-second periods. WiFi sensing can also detect stationary activities, a critical metric in public life studies; However, the accuracy determining whether a person stays or moves from WiFi data did not achieve a high level of accuracy, with an F1 score of 0.384. The findings show that it is possible to locate people’s positions, at least at a street level, and then determine their behaviors, moving and staying patterns, with moderate accuracy. Several examples concerning the rhythm of public life and shopping-travel behavior were presented as practical case studies, helpful in urban planning and design. In this thesis, I concluded that WiFi sensing provides an approximate location of people and their staying points with moderate accuracy. However, it effectively collects and analyzes long-term data at the neighborhood scale, supplementing the weaknesses mentioned above in manual observation. The analysis method proposed in this study improves the choice and range of research methods available for urban studies, expressly incorporating new sensing data and quantitative techniques into the standard toolkit of procedures used in public life studies. Specifically, the network of WiFi sensing with multiple sensors in a neighborhood can extend our understanding of public life beyond the named project area. This monitoring system also provides insights into how design elements, amenities, and programmed events enhance the vibrancy and vitality of public spaces by offering longitudinal evidence. This work contributes to transdisciplinary research on people’s mobility, which will in turn help to improve our overall understanding of cities, how they function, and how they are used in reality.

Secondary Organic Aerosol and Ozone Formation Potential from Anthropogenic and Biogenic Volatile Organic Compounds in Ulsan, South Korea, in Summer

Geunwoo Lee Ulsan National Institute of Science and Technology 2021 국내석사

A large quantity of anthropogenic and biogenic volatile organic compounds (VOCs) is emitted in Ulsan because Ulsan has huge multi-industrial complexes in its eastern coastal area and high mountainous regions in the western hinterland. Some of the VOCs are oxidized and form tropospheric ozone and secondary organic aerosol (SOA) in the atmosphere. Not only high temperature and radiation but also the transport of VOCs from their sources could aggravate the photochemical oxidation reactions in the atmosphere in Ulsan in summer. Despite the environmental importance of photochemical reactions of VOCs, few studies on photochemical VOCs in Ulsan have been carried out. The objectives of this study are to investigate the spatial concentration levels of photochemical VOCs, estimate the formation potentials of ozone and SOA, and propose further research to figure out how much VOCs have contributed to high tropospheric ozone and particulate matter episodes in Ulsan, South Korea, in summer. Hybrid VOC monitoring was conducted with diffusive passive samplers (Radiello, Instituti Clinici Scientifici Maugeri, Itay) and active pumped adsorbent tube samplers (Sequential tube sampler-25, PerkinElmer, UK) at 17 sites (5 industrial, 6 rural, 6 urban sites) and three sites (1 control, 1 industrial, 1 rural site), respectively, in Ulsan from May to August 2020. Through the hybrid VOC sampling, the temporal and spatial resolution of Ulsan VOC monitoring was highly improved. The target VOCs were selected as photochemical assessment monitoring stations (PAMS) ozone precursor 53 VOCs (36 aliphatics and 17 aromatics). Both anthropogenic VOCs like benzene, toluene, ethylbenzene, and o,m,p-xylene (BTEX) and a biogenic VOC, isoprene, were included. All 240 VOC adsorbent samples were analyzed with a thermal desorber-coupled gas chromatography/mass spectrometer (TD-GC/MS, UNITY series 2, Markes, UK-7890B/5977A, Agilent, USA). Every sampling trip had field blank samples to track any contaminations from the whole analytical process. A 3:1 signal to noise ratio was applied to the quantification of VOCs. The concentration spatiotemporal distribution of the VOCs was comprehensively interpreted with the data of 16 meteorological observation stations in Ulsan, considering the physicochemical properties of the 53 VOCs. From May to August, the atmospheric temperature in Ulsan increased except for in July because July is the rainy period. Heavy rain was observed in July, causing relatively low temperatures and radiation. Due to the land-sea breeze in Ulsan, the transport of VOCs from industrial areas to highly urbanized areas occurred in the daytime while transport of VOCs from mountainous areas to the urban region occurred in the nighttime. Criteria air pollutants (CAPs) in rural and industrial sites were compared. Although the concentration of fine particulate matter (PM2.5) did not show statistically significant differences between the sites, NO2 was higher, and O3 was lower in the industrial site than in the rural sites. Also, O3 and the fine particulate matter to coarse particulate matter (PM10) ratio, whose change could indicate the secondary aerosol formation, showed strong diurnal variations in the rural sites but not in the industrial site. These differences in the concentration levels of NO2 and O3 and the diurnal variation between industrial and rural sites need to be contemplated in a further SOA and O3 formation study in Ulsan. Total VOCs (TVOCs), BTEX, and aliphatics exhibited significantly higher concentrations in industrial sites than in rural and urban sites. However, isoprene, a well known biogenic VOC (BVOC), showed a higher concentration in rural sites than in industrial and urban sites. This was obvious due to the BVOCs being emitted from the vegetation. In addition, isoprene concentrations had strong diurnal cycles depending on temperature and solar radiation. In order to identify the source and aging status of BTEX in each site, diagnostic ratios were applied to the BTEX concentration in each sampling site. Toluene to benzene ratio and m,p-xylene to ethylbenzene ratio were used as indicators for traffic emission and aging, respectively. BTEX in automobile and shipbuilding industrial areas were highly affected by fresh and non-traffic sources while BTEX in the harborside petrochemical industrial area were mostly influenced by fresh and traffic sources. Most rural and urban sites were affected by aged both traffic and non-traffic BTEX sources. The top 5 VOC contributors of ozone and SOA formation potentials (OFP and SOAFP) in different sites were compared in this study. In urban and rural sites, toluene, ethylbenzene, and xylenes (TEX) were dominant in the top 5 OFP contributors. In addition to TEX, n-octane and 3-methylpentane significantly contributed to OFP in industrial sites. Regardless of the sites, TEX made the biggest contribution to SOAFP. OFP and SOAFP from VOCs were highest in petrochemical and automobile industrial areas, respectively, in this study. However, the estimated formation potential of O3 and SOA could not explain the spatiotemporal variations of O3 and SOA based on the observed data. To improve the accuracy of the estimations, more VOCs, especially BVOCs, should be included in VOC monitoring and a better methodology to calculate formation potential with meteorological conditions needs to be developed. In conclusion, TEX largely influenced OFP and SOAFP in Ulsan in the summer. While controls for TEX over the Ulsan need to be enhanced to reduce photochemical oxidation reactions forming O3 and SOA, the study on BVOCs such as isoprenes and terpenes, is also needed due to the lack of understanding BVOCs in Ulsan. In order to improve the estimation of O3 and SOA formation, the key factors, such as meteorological conditions and atmospheric composition, should be investigated and considered in a non-linear way like through a machine learning approach.

Machine Learning-Assisted Development of Multi-Component Organic Photovoltaics via High-Throughput In-Situ Formulation

Na Gyeong An Ulsan National Institute of Science and Technology 2021 국내박사

Organic photovoltaics (OPVs) have witnessed in next generation energy source due to their outstanding potentials such as light-weight, flexibility, semi-transparency, color-tunability and roll-to-roll (R2R) processability. In addition, OPVs have recently achieved great progress in power conversion efficiency (PCE) of >18%. One key breakthrough is an emergence of non-fullerene acceptors (NFAs), which allows easy tuning of energy level compared fullerene counterparts, give opportunity to explore high open-circuit voltages. A development of ternary system is further contributed to high performance of NFA-based OPVs, which enhances short-circuit current density from complementary absorption of two different donors or acceptors absorption region. Despite of such great advantages and achievements, current manufacturing technology known as one variable at a time experimentation (Edonesian) still has remained far behind the expectations in terms of time consuming and human resource. Therefore, high-throughput experimentation approach is highly in demand. This thesis covers NFA-based ternary OPVs and their applications with a new experimental approach; Firstly, a ternary combination consists of PTB7-Th, IEICO-4F and two simple NFAs based on a bithiophene core with rhodanine end-groups (T2-ORH and T2-OEHRH) were explored and their photovoltaic properties were systematically investigated. PTB7-Th and IEICO-4F are generally known as narrow band gap donor and acceptor and two NFAs retain ultra-wide ban gap, hence, the ternary systems were further utilized to achieve controllable device coloration. We successfully demonstrated blend films with tunable colors including cyan → blue → purple → reddish purple colors, which were controlled by the ratios of IEICO-4F:T2-ORH or IEICO-4F:T2-OEHRH with PTB7-Th. Additionally, optical properties of blend films were studied via absorption and transmission measurements, while the range of colors achieved was quantified using CIE chromaticity and CIELAB color space then represented as RGB color models. Next, we introduced a new research approach to develop OPVs via industrial R2R slot die coating in conjunction with in-situ formulation technique and machine learning (ML) technology. Various PM6:Y6:IT-4F ternary blends, one of the highest performing ternary systems to date, are formulated in-situ and deposited on continuously moving substrates resulting in high-throughput fabrication of OPV with various compositions. The system is used to produce training data of ML technology. Composition/deposition parameters, referred as deposition densities, and efficiencies of 2218 devices are used to screen ML algorithms and to train an ML model based on Random Forest regression algorithm. Generated model is used to predict high-performance formulations and the prediction is experimentally validated resulting in 10.2% efficiency, the highest efficiency from R2R processed OPVs to date.

Experimental analysis and hybrid predictive modeling of microhole drilled with high-energy electron beam on industrial materials

Hyunmin Park Ulsan National Institute of Science and Technology 2025 국내박사

Research on the Induction Heating Technology using Load Temperature Estimation and High-Voltage Output

GeunWook Kim Ulsan National Institute of Science and Technology 2022 국내석사

The induction heater directly applies electrical energy to the target and heats it by thermal energy conversion, unlike the conventional heating method. There are advantages of heating performance, high efficiency, and cleanliness through this. Unlike the existing fossil fuel combustion type, a current of AC frequency is generated through a coil to generate a magnetic field. This magnetic field forms an eddy current at the target, and heat is generated in the part where the current inside the target is generated. This operation procedure is different from making carbon gas such as coal and petroleum LPG as by-products. It has the advantage of not making flames and by-products accordingly, and safe heating is possible through electrical control. Application is roughly divided into domestic and industrial applications, and the research directions of the two fields are different. First of all, home applications focus on user convenience technology. For example, various studies have been conducted, such as a technology that enables operation in all-metal containers, a technology that reduces EMC emission caused by high frequency during operation, and estimating the temperature of the load. Among them, measuring the impedance of the load and estimating the temperature based on the impedance has expectations for automatic cooking in the future. Automatic cooking is a technique that informs the user of the recipe for the desired food and helps put the right ingredients at the right time. Estimating load impedance in the domestic cooker IH field to predict the state or temperature of cooking will serve as the basis for automatic cooking technology. In addition, it can be applied to secure safety by creating an alarm that informs water boiling alarm or overheating of the contents. In this thesis, user convenience technology has been studied for home applications by applying the above research direction. In industrial applications, research is being conducted to increase output power and speed up the heating of loads. The industry is demanding a method of increasing the temperature of the load by increasing output power rather than user convenience technology. To achieve a high output IH, an output voltage should be increased, and a device capable of operating at a constant frequency should be used. When a full-bridge inverter is implemented using a MOSFET device, there is a limitation in manufacturing high-power IH due to manufacturing a withstand voltage protection circuit and an increase in the unit price of a switching device. Using more switching elements, it is difficult to reconstruct a system suitable for the output power to expand the output capacity. This thesis proposes a method of stabilizing the system and easily extending the output by manufacturing an induction heating inverter in a modular manner and connecting input-parallel output-series. In this thesis, this study would like to present a design method for analyzing and producing induction heaters used as home cooking containers in the industry. In addition, for home cooking containers, user convenience technology was studied by adding impedance estimation technology. Industrial induction heaters constructed a modular inverter and increased the output voltage to study how to quickly heat and increase the range of operations that can be output. The above study was verified by simulation and experiment through a 2kW class induction heater.