The CTBTO is the Comprehensive Test Ban Treaty Organization to ban all forms of nuclear testing (underwater, air, and underground) worldwide and was adopted at the UN’s 50th annual general meeting in September 1996. As of September 2023, 187 out of 196 countries signed and 178 ratified. The Republic of Korea signed it in 1996 and ratified it in 1999. Several major Annex 2 countries still need to ratify it, and certain countries have not even signed it, so it has not come entry into force. The CTBTO has three verification systems for nuclear tests and consists of the International Monitoring System (IMS), the International Data Center (IDC), and On-Site Inspections (OSI). IMS consists of seismic, hydroacoustic, infrasound, and radionuclide monitoring. The measured data are delivered to IDC, analyzed by CTBTO headquarters, distributed raw data, and analyzed forms to member states. The final means of verification is in the field of OSI and will be operated when CTBT takes effect. Based on the IMS data, inspectors will be dispatched to the Inspected State Party (ISP) to check for nuclear tests. KINAC is attending the Working Group B, OSI technology development verification along with KINS and KIGAM. Since OSI is a means for final verification, integrated capabilities such as seismic and data interpretation and nuclides detection are required. CTBTO continues its efforts to foster integrated talent and modernize OSI equipment. Types of equipment include measurement, flight simulation equipment, and geographic information monitoring systems etcetera. KINAC is also developing equipment to detect contaminated areas using drones and probes. Development equipment is the nuclides detection and measurement of contaminated areas, and it is the equipment that prepares a control center and drops probes into suspected contamination areas to find a location of the radiation source. The probe can be used to track the location where the dose is most substantial through Bayesian estimation and source measurement.

Spent nuclear fuel continues to be generated domestically and abroad, and various studies are actively being conducted for interim dry storage and disposal of spent nuclear fuel. The characteristics vary depending on the type of spent nuclear fuel and the initial specifications, and based on these characteristics, it is essential to estimate the burnup and enrichment of spent nuclear fuel as a nondestructive assay. In particular, it is important to estimate the characteristics of spent nuclear fuel with non-destructive tests because destructive tests cannot be performed on all encapsulated spent nuclear fuel in case of intrusion traces in safeguards. Data is made by measuring spent nuclear fuel directly to evaluate burnup of spent nuclear fuel, but computer simulation research is also important to understand its characteristics because past burnup history is not accurately written, and destructive testing is difficult. In Sweden, the dependency of the burnup history in source strength and mass of light-water reactor-type spent nuclear fuel was evaluated, and this part was also applied to MAGNOX in consideration of the possibility of being used to verify DPRK’s denuclearization. SCALE 6.2 TRITON modeling was performed based on public information on DPRK’s 5 MWe Yongbyon reactor, and the source strength of Nb-95, Zr-95, Ru-106, Cs-134, Cs-137, Ce-141, Ce- 144, Eu-154 nuclides were evaluated. Since the burnup of MAGNOX is lower than that of lightwater reactors, major nuclides in decay heat were not considered. The cooling period was evaluated based on 0, 5, 10, and 20 years. In case the discharge timing was different, the total period of discharge and reloading was the same, and the end-cycle burnup was the same, calculations showed that the source strength emitted from major nuclides was evaluated within 2-3% except for Ru-106 and Ce-144 nuclides. Even the burnup step of nuclear fuel is the same, and the reloaded length after discharge is different, i.e., the cooling period between is different at 5, 10, and 20, the source strength of Nb-95, Zr-95, Ce-144, and Cs-137 was evaluated as an error of 1%. Except for Ru-106 and Ce-144, nuclides are highly dependent on burnup. Compared to the case of light-water reactors, the possibility of a decrease in error needs to be considered later because the specific power is low. As a result, radionuclides in released fuel depend on the effects of burnup, discharged and reloaded period, and a cooling period after release, and research is needed to correct the cooling period within the future burnup history. In addition, in this study, it is necessary to select a scenario -based burnup because the standard burnup due to the statistical treatment of discharged fuels was not considered as conducted in previous studies.

Any type of nuclear arms control or disarmament agreement requires some form of verification measure. Existing nuclear arms control treaties drew upon previous agreements such as the INF treaty, START, and IAEA nuclear safeguards inspections. However, previous treaties focused on limiting specific types of nuclear weapons and their delivery vehicles or reducing the total number of nuclear weapons rather than eliminating the nuclear enterprise as a whole. A potential nuclear disarmament verification treaty or agreement will depend on the geopolitical environment of the time as well as the national policies and priorities of each signatory state. Although research on the gradual reduction and eventual elimination of nuclear weapons is still ongoing, several states have cooperated to conduct experiments, exercises, and simulations on the procedures and technologies required for nuclear disarmament verification. Three of these efforts are the LETTERPRESS simulation conducted by the Quadrilateral Nuclear Verification Partnership (QUAD), NuDiVe Exercise conducted by the International Partnership for Nuclear Disarmament Verification (IPNDV), and the Menzingen experiment organized by the UNIDIR in partnership with the Swiss Armed Forces, Spiez Laboratory, Princeton University’s Program on Science and Global Security, and the Open Nuclear Network. These contain aspects for the development of a potential nuclear disarmament verification. The LETTERPRESS exercise conducted in 2017 tested potential activities and equipment inspectors might utilize in a nuclear weapon facility. The IPNDV NuDiVe exercises conducted in 2021 and 2022 tested the activities and equipment required for the verified dismantlement of a warhead within a dismantlement facility. Finally, the Menzingen experiment conducted in 2023 tested the practical procedures for the verification of a nuclear weapon’s absence at a storage site. This paper will analyze the three cases to offer considerations on the procedures and technologies future nuclear disarmament verification might include.

Arms control treaties during the Cold War generally used national technical means (NTM) to verify treaty compliance. This was because signatory states refused to agree on on-site inspection (OSI) measures since it would require some level of intrusion. Efforts on nuclear arms control such as the Limited Test Ban Treaty (LTBT) or Strategic Arms Limitation Talks (SALT) initially included some form of OSI but could not continue due to refusal from signatory states. The Intermediate-Range Nuclear Force (INF) treaty concluded between the US and the Soviet Union in 1978 was significant since both states agreed on a highly intrusive verification measure. The Strategic Arms Reduction Treaty (START) and the new START also called for OSI measures similar to the INF. Alongside reducing a significant number of nuclear warheads and limiting specific types of nuclear warhead delivery vehicles, these treaties also provided basic models for conducting on-site inspection (OSI). OSI measures primarily rely on the political agreement between signatory states. However, the structure, types of inspections, number of inspections allowed, and technology/equipment used in each of the regimes also differ according to the objectives of each treaty. The INF treaty and START are salient cases as basic models for current nuclear disarmament verification research. Thus, this paper will conduct a case study on the procedures and mechanisms required for nuclear arms control verification in terms of OSI. Using the implications drawn from the INF treaty and START, this paper offers considerations for a potential nuclear disarmament verification.

The Korea Institute of Nuclear Nonproliferation and Control (KINAC) is developing a simulation model to estimate nuclear material production. This model is a foundational technology in interpretation and evaluation in preparation for denuclearization verification. Through this model, it is possible to estimate the amount of nuclear material that can be produced based on information on the activities of facilities related to the nuclear fuel cycle in the actual denuclearization verification stage. This model makes it possible to determine whether the declared amount of nuclear material is reliable. In addition, the reliability of the reported information can be confirmed through on-site inspection. However, there is a possibility that proliferation-related activities cannot be detected even through this inspection, and a normal state may be misdiagnosed as carrying out nuclear proliferation-related activities. Therefore, it is unreasonable to specify activities related to nuclear proliferation with only one inspection. Since each inspection method has its diagnosis rate and false diagnosis rate, measures such as repeating the same inspection method or combining different inspection methods are required to detect activities related to nuclear proliferation reliably. Therefore, a model capable of estimating the number of repetitions to obtain a reliable nuclear activity detection probability was developed by using each inspection method’s diagnosis rate and false diagnosis rate as input information through a Bayesian inference method. Through this model, it can be concluded that repetitive inspections increase the probability of detecting nuclear proliferation-related activities. This approach confirmed the possibility of repeatedly breaking away from the high-intensity inspection method that causes political and diplomatic resistance from the target country and substituting it with a more readily acceptable, low-intensity inspection method.

The DPRK had been upgrading its nuclear weapons capabilities from the past to the sixth nuclear test in 2017, and Kim Jong-un has been in power since the death of Kim Jong-il in 2011, striving to upgrade and diversify four nuclear tests and firing means. In 2022, in particular, DPRK launched more than 40 ballistic and cruise missiles and provoked them in various ways, such as developing solid rocket engines, flying fighter jets, and invading drones. In addition, reprocessing facility activities have been observed again since 2021 at the Yongbyon Nuclear Research Complex. Operational activities such as continuous activities of the 5MWe Yongbyon reactor and the additional construction of new buildings are observed. DPRK’s recent activities could result in nuclear weapons in all except conventional weapons provocations. DPRK has researched and developed nuclear weapons since the 1950s. It has been preparing to operate nuclear weapons, operating nuclear power, and modernizing nuclear power simultaneously. Given the number of nuclear weapons using DPRK’s nuclear materials and various means of missiles, an offensive transition is expected to enable restrictive deterrence strategies that can be used first use and on assured retaliation. In addition, based on the nuclear strategy, which is interpreted as Vipin Narang’s nuclear doctrine and nuclear posture, DPRK is also capable of assured retaliation and asymmetric escalation posture. In particular, considering the continuous activities of the Yongbyon Nuclear Research Complex, which has recently diversified the investment vehicle, and the delegation of nuclear weapon use, it is expected to move differently from the previous one based on the changed nuclear strategy. However, there are clear limitations to interpreting it as a completely assured retaliation and asymmetric expansion nuclear strategy. First, there is a lack of development of atmospheric reentry vehicles that can avoid ICBM interception for assured retaliation capabilities against the United States. Second, there are limitations in the open capacity of nuclear weapons due to the absence of SSBN capabilities. However, delegation to operations at strategy force suggests the possibility of asymmetric expansion strategies. The previous analysis of DPRK’s nuclear strategy and limitations is valid in that the U.S. nuclear umbrella guarantees the Republic of Korea in a strong alliance between the Republic of Korea and the U.S. If the Republic of Korea lacks a nuclear umbrella due to the weakening of the alliance or limits U.S. intervention by having more than dozens of ICBMs, it is considered that DPRK can use a definite confirmation retaliation and asymmetric escalation nuclear strategy. As a response to this, it is the first way to verify and strengthen the validity of the three-axis system (Kill Chain, KAMD, KMPR), second to strengthen the Korea-U.S. alliance, and finally to appeal to the international community and increase consensus. In particular, it is possible to form a consensus of sanctions and condemnation DPRK by expressing concerns about nuclear dominoes caused by nuclear proliferation and arms competition to the international community.

Nuclear inspection is necessary to verify nuclear activities. If North Korea takes denuclearization, North Korea’s nuclear materials should be verified through non-destructive testing and destructive testing for nuclear material production. Since destructive testing of all substances is impossible, nondestructive testing is essential. Most non-destructive tests are performed by measuring the energy of gamma rays, but the characteristics of nuclear fuel can be evaluated by measuring neutron sources when enclosed with thick shields and when shielding structures are difficult to remove. Before the neutron source evaluation of MAGNOX used by North Korea, the relative characteristics will be evaluated later by analyzing the burnup, enrichment, and cooling time of the spent nuclear fuels discharged from the domestic nuclear power plant. This study evaluated the source strength and major nuclides according to burnup for the WH17×17 nuclear fuel assembly. The depletion calculation was conducted using SCALE 6.2 ORIGEN, and 3.5wt% enrichment, 10, 20, 30, 40, 50, 60 MWd/kg burnup, and five years cooling time, the minimum requirement for transport specified in the notice of the Nuclear Safety Commission, was applied. Although the impact assessment on enrichment should be evaluated with MCNP Tally to consider the fission reaction of the generated neutrons, this study only evaluated the spontaneous fission and (a, n) reactions that occurred first because it only evaluates the burnup impact. As burnup increased, neutron generation increased, and most of the total neutron strength occurred through spontaneous fission from the 10 MWd/kg burnup step. The influence of Pu-240 nuclides was dominant in the 10 MWd/kg burnup step but most neutrons were generated in tiny amounts of Cm- 244 generated from 20 MWd/kg burnup. Since DPRK’s 5 MWe Yongbyon MAGNOX has very low burnup (about 0.7 MWd/kg), the primary neutron sources of 10 MWd/kg, Am-241 and Pu isotopes, especially Pu-240, are expected to be used as indicators for evaluating spent nuclear fuel characteristics. If only specific nuclides are evaluated as major neutron sources at lower burnup than those evaluated in this study, in that case, the accuracy of non-destructive testing can be improved. Additionally, the evaluation according to the enrichment and cooling time should be considered as well.

Monitoring a state that intentionally hides its nuclear activity via open-source information is akin to looking through a black box. Direct information on the state’s nuclear activity remains in the dark, leaving scholars to speculate how much nuclear material or warheads are being produced. Nevertheless, a state’s nuclear program consists of a complex network that ranges from producing weapon-grade nuclear materials by operating its nuclear facilities to securing resources to fund these activities. These indirect activities allow a narrow window of opportunity for researchers to map a state’s activity that sometimes may not be directly linked to nuclear activity per se but is significant to maintaining and operating its nuclear program. These may include malicious cyberattacks to steal or launder cryptocurrency and facilitating cooperation with fellow rogue states that do not comply with the NPT and nuclear nonproliferation regime. The problem lies in how researchers can map this network. Much of the literature that uses text analysis uses data from either (1) formal statement, reports, and documents or (2) journal articles to extract relations between topics that is otherwise difficult to surmise. This study, however, analyzes news articles containing keywords related to a states’ nuclear activity such as international sanctions, trade activities, other states’ policy etc. While news articles fail to live up to the academic rigor of journal articles and unlike formal documents may sometime contain misinformation or incorrect facts, they are a valuable medium to show the day-to-day activity of a state. Although bias may exist as particular news articles may or may not be chosen for text analysis, by using articles collected from 2021 to 2022, this study argues it is enough data to show a short-term trend in nuclear activity.

This study installed and evaluated the efficiency of a radon barrier membrane, radon mat, and radon well in the removal and reduction of radon gas that originates from the soil and flows indoors. The study aims to present a fundamental and long-term solution to radon reduction in buildings by preventing soil radon, which is the main source of radon gas, from migrating indoors. A radon barrier membrane, radon mat, and radon well were developed and verified, and the radon reduction effect of each system was evaluated. Through applying a special radon gas blocking film with a 5-layer structure, the radon barrier membrane prevents radon gas particles from passing through the polymer deposited on the radon blocking film. The radon mat is a type of radon reduction construction method that induces radon gas generated from the soil under the building to move in the desired direction through the plate-structured pressure reducing panel and discharges radon gas to the outside of the building through an exhaust pipe and fan installed at the edge. In addition, the radon well can also be applied to special structures such as old buildings and historical sites where it is difficult to directly reduce radon concentration within the building foundation, because the intake area can be controlled and, therefore, the method can be applied in a variety of environments and ranges. In the case of Intervention 1 (installing a radon barrier membrane and radon mat), the soil radon was reduced by 24.7%. Intervention 2 (installing a radon barrier membrane, radon mat, and radon well) reduced the soil radon by 45.1%, indicating that the effect of reducing the soil radon concentration was 1.8 times higher compared with installing only the radon barrier membrane and radon mat. The measurement showed that the indoor radon concentration was reduced by 46.5%, following the reduction in soil radon concentration through Interventions 1 and 2, demonstrating the effect of reducing indoor radon gas by installing the radon barrier membrane, radon mat, and radon well. Through the production and installation of prototype systems, this study confirmed the reduction effect of radon concentration in soil and indoor air. These systems achieved a higher efficiency at a relatively low cost than that achieved with the existing radon reduction methods applied in Korea and abroad.

Bayesian statistics, which is an approach to analyzing data based on Bayes’ theorem, is currently widely used in all fields. However, it has been applied very limitedly to studies related to nuclear nonproliferation. Therefore, this paper provides a knowledge base and directions for using various Bayesian techniques in nuclear non-proliferation. First, the concepts and advantages of the Bayesian approach are summarized and the basic solving methods of Bayesian inference are explained. The Bayesian approach enables more precise posterior estimation using the prior probability and the likelihood functions. To solve Bayes’ theorem, it is necessary to use the conjugate prior distribution, which is analytically solvable, or to use a numerical approach with computing power. Next, for several Bayesian statistics methods, the purpose of use and the mathematical derivation process are described. Bayesian linear regression analysis aims for obtaining a function that outputs the closest value to data of variables and results. Factor analysis is mainly used to derive a smaller number of unobserved latent variables that can represent observed variables. The logit and probit model are nonlinear regression models for when the outcome is binary. The hierarchical model is to analyze by introducing hyper-parameters in an integrated manner when there are several groups of similar data. The Bayesian approach of these methods is generally based on the numerical solution of the Bayesian inference of the multivariate normal distribution. Finally, the previous researches that each introduced method have been applied to nuclear non-proliferation are investigated, and research topics that can be applied in the future are suggested. Bayesian statistics have been mainly used for precise estimation of the amount, location, and radioactivity spectrum of nuclear materials using detectors. Using Bayesian approach, it will be possible to perform various analyzes. For example, the change of activeness of nuclear program can be estimated by Bayesian inferences on the frequency and scale of nuclear tests. And it can be tried predicting the production of plutonium according to the core configuration and burnup using the Bayesian linear regression. Also, by introducing the Bayesian approach to factor analysis or logit analysis of nuclear development motives or nuclear proliferation probability, it can be expected to improve precision. With the development of computer technology, the use of Bayesian statistics increases rapidly. Based on the theory and applied topics summarized in this paper, it is expected that Bayesian statistics will be more actively used for nuclear non-proliferation in the future.

KINAC is trying to build a comprehensive aerial view of the nuclear material balance to predict North Korea’s weapons-grade nuclear material production capacity. We are creating a visualization model for North Korea’s nuclear facilities as part of these efforts. However, information on North Korea’s nuclear facilities is scarce, and it is not easy to consider additional facilities other than those already known. In addition, in the case of a model that targets only exceptional situations, it is not easy to secure objectivity for model validation, so it is necessary to upgrade to a general-purpose analysis tool that can be applied more generally. The following two examples are proposed as an analysis tool that can be a high degree of analysis. The first case is an Acquisition Path Analysis (APA) utilized to introduce IAEA’s State-Level Approach (SLA). The acquisition path analysis aims to find and evaluate the technically possible pathways to obtain nuclear materials for nuclear weapons or other nuclear explosive development. It can be an acquisition route if it is possible to produce at least 1 Significant Quantity (SQ) of weapongrade nuclear material within five years. The assessment of technologically feasible pathways is based on available information about the country’s past and present nuclear cycle capabilities. The second is the IAEA Physical Model. The IAEA Physical Model was carried out to introduce a comprehensive approach to all information on a country’s nuclear activities. It describes and characterizes the technologies and processes expressed at all levels of the acquisition path, depending on the development objectives. The IAEA Physical Model attempts a multi-tiered acquisition path analysis to identify all known technologies and processes in the nuclear fuel cycle, from raw material production to weapon usable material acquisition. Based on this analysis, the IAEA evaluates the signs of nuclear proliferation in a specific country. Based on the two cases discussed above, we intend to derive the following implications and priorities for extending the existing nuclear cycle model to a more general-purpose for a specific country. First of all, the requirements necessary to evaluate nuclear non-proliferation or verification of denuclearization must be at a level that the international community can recognize. In the stage of actual denuclearization verification, since verification will be conducted through the IAEA, a corresponding level of tools and technology will be required. From this point of view, the following is presented as a prerequisite for adding versatility to the existing physical model: It is necessary to derive all processes related to the nuclear cycle and standardize relevant indicators and data. In order to determine the signs of nuclear activity, detailed information on technologies, materials, by-products, and wastes, which are essential for each process, is required. For denuclearization verification, cumulative information from the past to the time point is required, and a comparative analysis of the operation history information of all facilities and the amount of nuclear material is required. To this end, it is necessary to make it possible to trace the history at every point where it can be determined that nuclear material has been diverted so that missing nuclear material can be found. Based on this, it is expected that it can be possible to evaluate a hypothetical threat state, but it is also expected that it will be easy to verify the model through the evaluation of easily accessible domestic facilities.

본 연구에서는 광화학 대기질 모델인 CMAQ을 활용해 화력발전소 배출량 제거에 따른 O3 농도의 변화 특성을 분석하였다. 하동 화력발전소를 대상으로 주변 지역의 O3 농도 변화에 대한 발전소 배출량의 영향을 조사하기 위해 하 동 화력발전소의 배출량 제거 전과 후의 CMAQ 수치 모의를 수행하였다. 수치 모의 결과 O3의 주요 전구 물질인 NOx (-18.87%)와 VOCs (-11.27%)의 농도가 감소한 반면에 O3 (25.24%)의 농도는 증가한 것으로 나타났다. 화력발전소 배출량 제거로 인한 NO와 O3 농도의 상대적인 변화를 비교해 본 결과 높은 음의 상관관계(R= -0.72)를 나타내는 것이 확인되었다. 이러한 결과는 O3의 농도 증가가 NO 농도 감소로 인한 O3의 적정 효과 완화로 설명 될 수 있음을 의미한 다. 해당 지역의 O3의 농도 증가가 NO의 농도 감소에 주로 영향을 받은 이유는 해당 지역이 VOC-limited (i.e., NOxsaturated) 지역이기 때문으로 분석되었다. 이러한 결과는 특정 지역의 O3의 농도가 단순히 배출량의 증감에 따라 비례하게 나타나지 않을 수 있다는 것을 암시한다. 따라서 화력발전소 배출량 저감 조치로 인한 대기 중 O3 농도 개선 효과를 정확히 예측 및 평가하기 위해서는 지역 별 O3의 생성 및 소멸 기작에 대한 심도 있는 이해가 필요하다.

유류와 위험 유해물질(Hazardous and Noxious Substances, 이하 HNS)을 포함하는 위험물질의 해상운송 중에 발생하는 사고가 증가하고 있어, 이러한 위험물질 해양사고를 방지할 수 있는 예방대책을 마련해야 할 것이다. 이를 위해 국내에서 발생하는 위험물질 해양사고 자료(2002~2014)를 수집하여 인명 및 환경 위험도를 분석하였으며, 사고원인 규명 및 적절한 예방대책이 필요한 우선 안전관 리분야를 파악하고자 하였다. 인명위험도는 선박 수리 및 탱커세정(tank cleaning) 작업과정에서 발생하는 폭발 및 인명사고 중 질식 등 이 높은 것으로 분석되었다. 환경위험도는 충돌, 좌초 등에 의한 유출사고로 인해 발생하였다. 또한 비포장 상태의 위험화물을 선박에 적재 중 취급부주의로 인하여 유출사고가 일어났다. 다수의 사고는 적합한 안전장비 미착용, 취급 부주의 등 인적오류로 인한 사고로 서 관리·감독을 강화하고, 주기적인 교육·훈련을 통하여 사고 저감이 가능하다. 위험물질 해양사고를 예방하기 위해서는 물질 자체 고 유의 특성상 유해성과 위험성을 지닌 위험물질(유류와 HNS)에 대한 안전관리를 더욱 강화해야 한다.

역삼투막 운영에 있어서 유기물 오염에 대한 문제들을 해결하기 위해 많은 연구를 하고 있다. 현재 가성소다 (NaOH)를 사용하여 유기물 오염 제거를 하고 있다. 본 연구는 지속적인 막오염 증가 문제를 해결하기 위한 물리/화학적 세정 기법으로서 기존에 사용하던 가성소다와 Micro-bubble를 이용하여 유기물 오염 제거 실험을 수행되었다. 멤브레인 강제 오염 을 위해 Humic acid sodium, Bovine serum albumin, Sodium alginate 약품을 사용하여 유기물 오염을 시켰다. 유기물 오염에 따른 Flux를 관찰하였고, 가성소다와 Micro-bubble를 이용한 유기물 오염 제거 실험은 가성소다로만 사용했을 때보다 향상 된 것을 관찰했다.

In this study, numerical simulations using community multiscale air quality (CMAQ) were conducted to analyze the change in ozone (O3) concentration due to the reduction in nitrogen oxides (NOx) and volatile organic compounds (VOCs) emissions in Busan. When the NOx and, VOCs emissions were reduced by 40% and, 31%, respectively, the average O3 concentration increased by 4.24 ppb, with the highest O3 change observed in the central region (4.59 ppb). This was attributed to the decrease in O3 titration by nitric oxide (NO) due to the reduction of NOx emissions in Busan, which is classified as a VOCs-limited area. The distribution of O3 concentration changes was closely related to NOx emissions per area, and inland emissions were highly correlated with daily maximum concentrations and 8-h average O3 concentrations. Contrastingly, the effect of emission reduction depended on the wind direction. This suggests that the emission reduction effects may vary depending on the environmental conditions. Further research is needed to comprehensively analyze the emission reduction effects in Busan.

In this study, we quantitatively analyze the effect of ocean emission sources on the simulated O3 concentrations in South Korea using the community multi-scale air quality (CMAQ) model. To analyze changes in O3 concentrations by ocean emissions, two different CMAQ simulations considering ocean emissions (OE case) and without considering ocean emissions (NE case) were conducted during the Korea-United States air quality (KORUS-AQ) campaign period (May–June 2016). The changes in the simulated O3 concentrations due to the effect of ocean emissions (OE case-NE case) appeared mostly in the ocean areas (+1.201 ppbv). The effect of ocean emissions was positive during the daytime (+1.813 ppbv), but negative during the nighttime (–0.612 ppbv). Analysis using the integrated process rate (IPR) confirmed that the increase or decrease in O3 concentration by ocean emissions was mainly due to chemical processes. Further analysis using the integrated reaction rate (IRR) showed that the daytime increase in O3 concentration was mainly attributable to the increased O3 production via O + O2 + M → O3 + M reaction as photolysis of NO2 increased due to the added ocean emissions. The nighttime decrease in O3 concentration was mainly due to the increased O3 titration by NO (NO + O3 → O2 + NO2) due to the increased NO emission. These results indicate that the changes in the concentration O3 in the sea area by the effect of ocean emissions are mainly due to increased NOx emissions. However, there could be a number of uncertainties in ocean emissions data used in this study, thus continuous comparative research using the most updated data will need to be carried out in the future.