Obesity Can Contribute to Severe Persistent Allergic Rhinitis in Children through Leptin and Interleukin-1ß.

BACKGROUND: Obesity/overweight is associated with a higher risk of allergic rhinitis (AR) in children. OBJECTIVE: This study aimed at exploring the mechanisms by which obesity affects the severity of AR through leptin and interleukin (IL)-1ß were investigated. METHODS: In all, 210 subjects with AR and 82 subjects without AR were included in this study. The levels of leptin and inflammatory biomarkers were measured in the serum to investigate the correlation with the severity of AR. Additionally, we analyzed whether changes in BMI regulate the severity of AR through serial follow-up of obese children. RESULTS: IL-1ß, which is a biomarker of active inflammation in AR, was significantly higher in individuals with AR than in those without and higher in subjects in the obesity group than in those in the normal weight group. A regression analysis showed that the leptin level was associated with increased IL-1ß expression in children with AR. In the multivariate analysis, only parental AR (9.2-fold increase in risk), elevated leptin (11.3-fold increase in risk), and high expression of IL-1ß (5.8-fold increase in risk) emerged as significant risk factors of moderate to severe persistent allergic rhinitis. We also found that children with an increase or decrease in BMI showed changes in IL-1ß and AR symptoms, which these changes were dependent on leptin and BMI. CONCLUSIONS: These results suggest that obesity is an important risk factor for the exacerbation of symptoms and leptin can exacerbate inflammation as well as severe and persistent symptoms through IL-1ß in AR.

Perinatal factors and the development of childhood asthma.

BACKGROUND: Perinatal factors are suspected to have a significant impact on the development of asthma; however, sufficiently powered studies have not been performed to investigate this issue. OBJECTIVE: To evaluate whether perinatal factors and other risk factors have an independent or combined effect on the development of asthma. METHODS: This study involved 3,770 children (mean age 9.1 years, range 5.68-12.16 years; 51.9% boys) who were enrolled in the Elementary School Student Cohort (2009-2014) in Ulsan University Hospital (Ulsan, Korea). Subjects were divided into an asthma group (n = 514) and a non-asthma group (n = 3,256). RESULTS: Multivariate analyses showed that early life (within first week) oxygen therapy (adjusted odds ratio [aOR] 1.864, 95% confidence interval [CI] 1.156-3.004) and breastfeeding (aOR 0.763, 95% CI 0.606-0.960) were 2 significant perinatal factors influencing the development of asthma. Environmental tobacco smoke (aOR 1.634, 95% CI 1.298-2.058) and parental allergic disease (aOR 1.882, 95% CI 1.521-2.328) also were identified as risk factors. Using subgroup analyses, combined effects on asthma development were observed between perinatal factors (early life oxygen therapy and breastfeeding) and other risk factors (vicinity to major roadway [traffic-related air pollution], environmental tobacco smoke, parental allergic disease, and atopy). CONCLUSION: Early life oxygen therapy and breastfeeding were identified as 2 important perinatal factors influencing the development of asthma. Furthermore, these factors showed combined effects with other risk factors (environmental tobacco smoke, traffic-related air pollution, parental allergic disease, and atopy) on the development of asthma.

Association between particulate matter concentration and symptoms of atopic dermatitis in children living in an industrial urban area of South Korea.

INTRODUCTION: Increased exposure to particulate matter (PM) appears to increase the development of atopic diseases and allergic sensitization. This study evaluated the association between daily levels of PM with diameters less than 10µm (PM10) and PM2.5 and symptoms of atopic dermatitis (AD) in children living in an industrial urban area. METHODS: Indoor PM10 and PM2.5 concentrations were measured with an optical particle counter in two preschools near large industrial complexes in Ulsan, South Korea during two 6-month periods (May-October of 2012 and 2013). Twenty-one children with AD from these preschools were enrolled and observed daily for AD symptoms during the same periods. Indoor and outdoor PM concentrations were used to estimate PM exposure based on time activity patterns. RESULTS: Analysis of PM10 and PM2.5 concentrations showed that indoor and outdoor PM10 levels varied similarly throughout each 6-month period. In addition, indoor concentration of PM2.5 had high correlation with ambient outdoor concentration of PM10. Correlation analysis also indicated a significant positive correlation between the exacerbation of AD symptoms and daily mean exposure to PM10 and PM2.5. Based on a generalized linear mixed model (GLMM), PM exposure was significantly associated with the exacerbation of AD symptoms, with a maximum adjusted odds ratio (aOR) of 1.399 for a 10µg/m3 increase of PM2.5 (95% CI: 1.216-1.610). DISCUSSION: Our findings suggest that short-term exposure to PM can exacerbate AD in young children living in an industrial urban area. PM2.5 had a stronger effect than PM10 on exacerbation of AD symptoms.

Environmental and Body Concentrations of Heavy Metals at Sites Near and Distant from Industrial Complexes in Ulsan, Korea.

BACKGROUND: Industrial pollution may affect the heavy metal body burden of people living near industrial complexes. We determined the average concentrations of atmospheric heavy metals in areas close to and distant from industrial complexes in Korea, and the body concentrations of these heavy metals in residents living near and distant from these facilities. METHODS: The atmospheric data of heavy metals (lead and cadmium) were from the Regional Air Monitoring Network in Ulsan. We recruited 1,148 participants, 872 who lived near an industrial complex ("exposed" group) and 276 who lived distant from industrial complexes ("non-exposed" group), and measured their concentrations of blood lead, urinary cadmium, and urinary total mercury. RESULTS: The results showed that atmospheric and human concentrations of heavy metals were higher in areas near industrial complexes. In addition, residents living near industrial complexes had higher individual and combined concentrations (cadmium + lead + mercury) of heavy metals. CONCLUSION: We conclude that residents living near industrial complexes are exposed to high concentrations of heavy metals, and should be carefully monitored.

Association of carbon monoxide levels with allergic diseases in children.

BACKGROUND: Air pollution is regarded as a potential reason for the development or aggravation of allergic diseases. OBJECTIVE: To investigate the relationship between exposure to outdoor air pollution during the first year of life and the development of allergic diseases, and to determine the association between outdoor air pollution near the residence and recent symptoms of allergic diseases in children. METHODS: A nationwide cross-sectional survey was conducted in 6- to 7-year-old children. Among them, subjects who had been born (n = 1828) or lived (n = 1894) within 2 km of the nearest air quality monitoring sites were selected. The prevalence of allergic diseases was assessed by using questionnaires. Each subject was examined by pediatricians to determine the presence of eczema. Publicly available data were used regarding the daily ambient concentrations of sulfur dioxide, nitrogen dioxide, ozone, carbon monoxide (CO), and particulate matter. RESULTS: For a 100 ppb increase in the mean daily CO level during the first year of life, the adjusted odds ratio for lifetime allergic rhinitis was 1.10 (95% confidence interval, 1.03-1.19). For a 1 ppm increase in the annual average CO level during the past 12 months, the adjusted odds ratio for the presence of atopic dermatitis on the day of the survey was 8.11 (95% confidence interval, 1.06-62.12). However, the other air pollutants showed no statistical significance. CONCLUSIONS: Higher exposure to CO during infancy increased the risk of development of allergic rhinitis. The risk of current atopic dermatitis symptoms increased in children who were exposed to higher CO levels during the past 12 months.

Oxidative stress in schoolchildren with allergic rhinitis: propensity score matching case-control study.

BACKGROUND: Oxidative stress is defined as an imbalance between the level of reactive oxygen species and antioxidant mechanisms. Compared with asthma, the role of oxidative stress in allergic rhinitis (AR) has received little attention. OBJECTIVE: To investigate the association between overall systemic oxidative stress and AR. METHODS: We used a propensity score matching case-control study and selected 90 children who had experienced AR in the previous year. This AR group was then matched with 90 healthy children who comprised the control group. Propensity score matching, a statistical matching technique that accounts for the conditional probability of receiving an exposure given a vector of measured covariates, is used to reduce selection bias and potential confounders in observational study. Serum total antioxidant status (TAS) and total oxidant status (TOS) levels were determined using a commercially available assay kit. Medical records and personal information were also reviewed. RESULTS: No statistically significant differences were found between patients with regard to age, sex, height, weight, educational level of parent, monthly household income, or distance of home from a main road. The mean TAS and TOS levels in the patient group were significantly higher than those of the control group (P = .03 and .048, respectively). The oxidative stress index, which is defined as the ratio of TOS to TAS, also increased in the AR group with statistical propensity (P = .08). In a multivariate logistic analysis, only TAS and TOS levels were significantly associated with increased risk of allergic rhinitis. CONCLUSION: Patients with AR have systemically elevated oxidative stress and systemically elevated TAS levels.

IL-1ß and iNOS can drive the asthmatic comorbidities and decrease of lung function in perennial allergic rhinitis children.

BACKGROUND: Allergic asthma and rhinitis (AR) are closely linked, with a significant proportion of AR patients developing asthma. Identification of the early signs of comorbidity of AR and asthma can enable prompt treatment and prevent asthma progression. OBJECTIVES AND METHODS: This study investigated the role of interleukin-1ß (IL-1ß), a pro-inflammatory cytokine, and inducible nitric oxide synthase (iNOS) in the comorbidity of AR and asthma and lung function in Korean children with perennial AR (PAR). A cohort of 240 subjects (6 to 10 years old) with PAR (PAR alone: 113 children, PAR and asthma: 127 children) was analyzed for various biomarkers, including IL-1ß, iNOS, and epithelial-mesenchymal transition (EMT) markers in serum. The blood levels of eosinophils and immunoglobulin E (IgE) were examined. IL-1ß, CCL-24, E-cadherin, and vimentin were measured by enzyme-linked immunosorbent assay (ELISA). Epithelial iNOS was measured by the NOS kit. RESULTS: Elevated levels of IL-1ß, iNOS, and vimentin in the serum were identified as significant indicators of the likelihood of comorbidity of PAR and asthma in children. Furthermore, higher concentrations of IL-1ß, iNOS, and vimentin have been linked to reduced lung function in PAR children. Notably, IL-1ß expression shows a relationship with the levels of E-cadherin, vimentin, and CCL-24. However, no correlation was found between IL-1ß and iNOS expressions. CONCLUSIONS: This study suggests that IL-1ß and iNOS can be biomarkers in the progression of PAR and asthma and decreased lung function, suggesting potential targets for early intervention and treatment.

A Prospective Study on the Association between Oxidative Stress and Duration of Symptoms in Allergic Rhinitis.

Oxidative stress has been known to play an important role in inflammatory responses of allergic rhinitis. We investigated the association between degree of oxidative stress and severity of allergic rhinitis. A total 226 allergic rhinitis students were classified by a history of allergic rhinitis into groups according to number and duration of symptoms within the previous year. The total antioxidant status (TAS) and total oxidant status (TOS) levels were compared among groups. Mean TAS level (14.03 ± 9.09 mmol/L) in the group with more than six months of symptoms had a tendency to be higher (p = 0.068) than that of the group with fewer than six months (12.33 ± 8.83 mmol/L). There was no statistically significant difference in mean TAS or TOS level with number of symptoms (nasal congestion, itching, sneezing and watery rhinorrhea). A multivariate logistic regression showed that the adjusted odds ratio of TAS was 1.655 and the adjusted odds ratio of TOS was 0.972 in more than a six-month duration group. The TAS level was significantly associated with a more than six-month symptom duration (p = 0.034). Our results suggest that antioxidant activity increased when allergic rhinitis became chronic and further research will be needed considering the disease severity.

Comprehensive study of a long-lasting severe haze in Seoul megacity and its impacts on fine particulate matter and health.

A long-lasting severe haze event was observed over the Seoul metropolitan region (SMR: Seoul, Incheon, and Gyeonggi-do), South Korea, in the winter of 2013 (January 12-16). We comprehensively investigated the atmospheric processes affecting particulate matter (PM) distributions during the haze event, as well as its impact on human health in the study area. These analyses were performed based on meteorological and PM observations and numerical modeling, which included the WRF-CMAQ modeling system and the Environmental Benefits Mapping and Analysis Program-Community Edition (BenMAP-CE). High PM10 concentrations during the haze event were mostly observed in the western and southern parts of the SMR. Significant differences (60-70 µg m-3) in the mean PM2.5 concentrations for haze and non-haze days were predicted mainly in the west-northwest areas of SMR. This might be primarily due to the pollutant transport (horizontal and vertical) from large emission sources (e.g., Chinese emissions) and, in part, their local accumulation (by local emissions) under high-pressure conditions and slow-moving air flows (i.e., blocking effect) around SMR. In addition, the enhanced PM2.5 concentrations in the study area during the haze event led to an increase in the number of premature deaths.

Allergic rhinitis is associated with atmospheric SO2: Follow-up study of children from elementary schools in Ulsan, Korea.

OBJECTIVES: The purpose of this study was to examine the association of allergic rhinitis with air pollutant concentrations using the follow-up data of elementary school children in Ulsan, Korea. METHODS: All students of four elementary schools in Ulsan, South Korea were surveyed at two-year intervals. The survey used data collected five times, over a nine-year period from June 2009 to April 2018. The questionnaire used in the survey was a modified version of the ISAAC (International society of asthma and allergy of children) questionnaire. A skin prick test (SPT) was performed with 24 standard antigens. To estimate the levels of exposure to outdoor air pollution, the concentrations of sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), carbon monoxide (CO), and particulate matter 10 µm or less in diameter (PM10) were used. As a dependent variable, a history of allergic rhinitis diagnosed by a doctor during the last 1-year was considered. Logistic regression analysis was used to select variables suitable for the statistical model. The selected variables were then used to assess their association with the dependent variable using the generalized estimation equation. RESULTS: Among environmental factors, SO2 was associated with a high risk and PM10 was associated with a low risk of allergic rhinitis. The risk of allergic rhinitis from living in a house built within the last year was high, and the risk from living in a multi-family house or apartment was higher than that from living in a segregated house. History of allergic diseases in the family was a high-risk factor for allergic rhinitis. There was a relationship between a history of bronchiolitis at less than 2 years of age and a high risk of allergic rhinitis. Boys were at a higher risk than girls. CONCLUSION: From the follow-up data of elementary school students in Ulsan, Korea, the concentration of SO2, which is an indicator of the degree of industrialization, was related to the prevalence of allergic rhinitis. Among all the risk factors, history of allergic disease in the parents was the most important factor, and the study reconfirmed the results of the previous studies.

Impact of Environmental Factors on the Prevalence Changes of Allergic Diseases in Elementary School Students in Ulsan, Korea: A Longitudinal Study.

We examined the effect of long-term changes in environmental factors on the prevalence of allergic diseases in elementary school students in Ulsan, Korea. This longitudinal study was conducted among 390 students who were enrolled from three elementary schools in Ulsan in both the first (2009-2010) and second survey (2013-2014). The International Study of Asthma and Allergies in Childhood questionnaire was used to determine the prevalence of allergic diseases and hazardous environmental factors. Generalized estimating equations (GEE) were used to investigate the impact of environmental factors on the change in the prevalence of allergic diseases. The survey revealed that an increased risk of allergic rhinitis was associated with exposure to secondhand smoke, the remodeling of a room, the replacement of wallpaper or flooring, the use of a humidifier, and irritation symptoms of air pollution. Atopic dermatitis was associated with the relocation to or repairs of a new house, and allergic conjunctivitis was associated with low levels of weekly physical activity, the use of insecticides, and irritation symptoms of air pollution. The results indicate that (1) allergic rhinitis and atopic dermatitis are associated with indoor pollution, (2) allergic conjunctivitis is associated with exposure to indoor chemical compounds and low levels of weekly physical activity. This study suggested that the proper evaluation and decrease in the number of environmental risk factors could effectively manage allergic diseases.

Serum IL-1ß can be a biomarker in children with severe persistent allergic rhinitis.

BACKGROUND: Allergic rhinitis (AR) is one of the most common diseases globally and usually persists throughout life. In the present study, we aimed to determine whether the expression of inflammatory biomarkers has a relationship with the severity of allergic rhinitis and with comorbid asthma or other allergic diseases in children. METHODS: For diagnosis of AR, the skin prick test was performed to measure the responses to 18 allergens. Blood levels of eosinophils and immunoglobulin E (IgE) were examined. We classified the patients into 2 groups based on the severity of the condition as Group 1 [intermittent AR (IAR) or mild persistent AR (PAR)] and Group 2 (moderate to severe PAR). To determine the expression of inflammatory biomarkers, in serum and several biomarkers (caspase-1, IL-1ß, CCL-11, CCL-24 and IL-33) were measured in the serum using enzyme-linked immunosorbent assay (ELISA). Additionally, we analyzed the correlation between clinical variables and the expression of biomarkers (eosinophils count, IL-1ß and CCL-24) and the severity of AR. RESULTS: We found that eosinophils count, IL-1ß, a marker of activation of inflammasomes, and CCL-24 were significantly increased in the moderate to severe PAR group (p = 0.008, p = 0.003, p = 0.039). Additionally, the expressions of eosinophil count, IL-1ß and CCL-24 were significantly higher in patients with active asthmatic symptoms than in those without these conditions. On univariate analysis, allergic rhinitis in sibling, paternal allergic rhinitis, high expression of eosinophils count, IL-1ß and CCL-24, history of active asthma and atopy correlated with severity of AR. Multivariate analysis showed only paternal allergic rhinitis and high expression of IL-1ß as significant risk factors of moderate to severe PAR with 6.4 fold and 4.7 fold-increase in risk, respectively (p = 0.011 and p = 0.030). CONCLUSION: In conclusion, this study provides the first evidence that an excessive release of biologically active IL-1ß may promote inflammation in severe PAR. It demonstrates that IL-1ß can be a biomarker for active allergic diseases such as AR, asthma, and atopy. Moreover, this finding suggests that IL-1B should be investigated as a therapeutic target in severe PAR and other allergic diseases.

Changes of Atmospheric and Blood Concentrations of Lead and Cadmium in the General Population of South Korea from 2008 to 2017.

We measured changes in atmospheric and blood levels of lead and cadmium in the South Korean general population during the past decade. Blood data of 16,873 adults were taken from the Korean National Health and Nutrition Examination Survey (KNHANES, 2008-2017). Atmospheric data were taken from 66 air quality monitoring sites in 16 different regions in South Korea. From 2008 to 2017, the geometric mean (GM) blood lead level decreased from 2.37 to 1.46 µg/dL (38.4% decrease), and the atmospheric lead concentration decreased by 61.0% in the overall population. During this time, the GM blood cadmium level decreased from 0.88 to 0.72 µg/L (18.2% decrease), and the atmospheric cadmium concentration decreased by 63.6%. Multiple linear regression analysis indicated that a half reduction in air lead was associated with a 0.09 µg/dL decrease in blood lead (95% CI: 0.03 to 0.15) in a subgroup of the metropolitan city population. However, a half reduction in air cadmium had no significant effect on blood cadmium. Multiple linear regression analyses indicated that the decrease in blood lead level over 10 years in Korea was related to the decrease in atmospheric lead concentration. However, the decrease in blood cadmium level during this time was not significantly associated with the decrease in atmospheric cadmium concentration. Our findings suggest that inhalation is a major source of lead exposure, but not of cadmium exposure. Ingestion of dietary cadmium presumably has a stronger impact on blood cadmium levels.

Astigmatism Associated with Allergic Conjunctivitis in Urban School Children.

INTRODUCTION: We first examined the association of an ocular refractive error with allergic conjunctivitis in school children and then examined this association in children attending a suburban school and an urban school. METHODS: We enrolled 426 children attending a primary school in a suburban area and 550 children attending a primary school in an urban area which had a higher level of air pollution. Allergic conjunctivitis was defined as the diagnosis of this condition at any time during a child's life. The ophthalmic examinations included measurements of visual acuity and refraction, and a slit lamp examination. Skin prick tests were also performed at each school during 2018. The significance of associations was determined by the calculation of odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS: Astigmatism (increase of 1 cylindrical diopter) was associated with allergic conjunctivitis in children overall (OR = 1.287, 95% CI = 1.010 to 1.642) and in children attending the urban school (OR = 1.408, 95% CI = 1.029 to 1.926), but not in children attending the suburban school (OR = 1.040, 95% CI = 0.672 to 1.610). Allergic conjunctivitis also had a higher prevalence among children attending the urban school. The urban school had higher levels of air pollutants than the suburban school. Skin prick tests indicated that the major allergens in children with allergic conjunctivitis were house dust mites and various types of pollen. CONCLUSION: Astigmatism is associated with allergic conjunctivitis in children attending an urban school.

Source apportionment of VOCs and their impact on air quality and health in the megacity of Seoul.

The source apportionment of volatile organic compounds (VOCs) was examined using receptor models (positive matrix factorization and chemical mass balance) and a chemical transport model (CTM). The receptor model-based analysis was performed using the datasets collected from four different sites from the megacity of Seoul during the years 2013-2015. The contributions of VOC emission sources to ozone (O3) and PM2.5 concentrations and the subsequent health effects in the study area were also assessed during a photochemically active period (June 2015) using a three-dimensional CTM, Community Multi-scale Air Quality (CMAQ), and the Environmental Benefits Mapping and Analysis Program (BenMAP). The solvent use and the on-road mobile emission sources were found to exert dominant controls on the VOC levels observed in the target city. VOCs transported from regions outside of Seoul accounted for a significant proportion (up to approximately 35%) of ambient VOC levels during the study period. The solvent use accounted for 3.4% of the ambient O3 concentrations during the day (daily mean of 2.6%) and made insignificant contributions to PM2.5 (<1%) during the simulation period. Biogenic VOC made insignificant contributions to O3 (<1%) and a small contribution to PM2.5 during the day (5.6% with a daily mean of 2.4%). The number of premature deaths attributed indirectly (O3 and PM2.5 formations via the oxidation of VOCs) to solvent use is expected to be significant.

Comparison of a 10-Year Cumulative Age-Standardized Incidence Rate of Lung Cancer among Metropolitan Cities in Korea (During the 2000⁻2009 Period): Review of Occupational and Environmental Hazards Associated with Lung Cancer.

In Korea, lung cancer is a common cancer, and has the highest mortality rate in both males and females. Approximately 80% of lung cancer is due to smoking, and the remaining cases are known to be due to genetic factors, history of respiratory disease, infection, diet, and occupational and environmental factors. Since the occupational and environmental hazards may differ from region to region, the lung cancer risk may differ too. To identify this, we selected seven metropolitan cities, and compared occupational and environmental hazards. Furthermore, we calculated smoking rate adjusted standardized rate ratio (ratio of 10-year cumulative age-standardized incidence rate of lung cancer during the 2000⁻2009 period at target region versus reference region) to compare the regional lung cancer risk. The result showed that the emissions and concentrations of air pollutant were higher in high-risk regions, and the risk of lung cancer was significantly elevated in such area. In this study, we simultaneously consider the cumulative incidence, age-standardization and smoking rate adjustment. Therefore, we can conclude that the validity of the finding of this study is higher than that of past studies. In conclusion, the occupational and environmental hazards have an effect on lung cancer.

Perceptions regarding utilization of meteorological information in healthcare in Korea: a qualitative study.

BACKGROUND: Health forecasting has been used in an attempt to provide timely and tailored meteorological information to patients and healthcare providers so that they might take appropriate actions to mitigate health risks and manage healthcare-related needs. This study examined the in-depth perceptions of healthcare providers and the general public regarding the utilization of meteorological information in the healthcare system in Korea. METHODS: The COREQ (Consolidated Criteria for Reporting Qualitative Research) checklist was applied to this study. We conducted three focus group discussions in accordance with semi-structured guidelines developed to deal with various aspects of the utilization of meteorological information in healthcare settings. The verbatim transcriptions and field notes were analyzed according to content analysis. RESULTS: Six physicians, four nurses, three emergency medical technicians, and seven members of the general public participated in the focus group discussions. There were some individual discrepancies among most participants regarding the health effects of climate change. Although several physician participants felt that meteorological information utilization is not a prime concern during patient care, most of the general public participants believed that it should be used in the patient care process. The provision of meteorological information to patients undergoing care is expected to not only improve the effective management of climate-sensitive diseases, but also boost rapport between healthcare providers and patients. CONCLUSIONS: More attempts should be made to provide meteorological information to groups vulnerable to climate change, and the effects of this information should be evaluated in terms of effectiveness and inequality. The findings of this study will be helpful in countries and institutions trying to introduce health forecasting services.

Correction to: Perceptions regarding utilization of meteorological information in healthcare in Korea: a qualitative study.

[This corrects the article DOI: 10.1186/s40557-018-0214-3.].

Identification and interpretation of representative ozone distributions in association with the sea breeze from different synoptic winds over the coastal urban area in Korea.

To aid the studies of long-term impact assessment of cumulative ozone (O3) exposures, the representative 8-hr O3 pollution patterns have been identified over the Greater Seoul Area (GSA) in Korea. Principal component analysis and two-stage clustering techniques were used to identify the representative O3 patterns, and numerical and observational analyses were also used to interpret the identified horizontal distribution patterns. The results yielded three major O3 distribution patterns, and each of the three patterns was found to have strong correlations with local and synoptic meteorological conditions over the GSA. For example, pattern 1, accounting for 46% of O3 concentration distributions, mostly occurred under relatively weak westerly synoptic winds. The predominant features of this pattern were infrequent high O3 levels but a distinct gradient of O3 concentration from the western coastal area to the eastern inland area that was mainly induced by the local sea breeze. Pattern 2, accounting for 31% of O3 concentration distributions, was found with higher O3 levels in the western coastal area but lower in the eastern inland area. This is due to the modified sea breeze under the relatively stronger easterly opposing synoptic wind, affecting the high O3 occurrence in the western coastal area only. However, pattern 3, accounting for 21% of O3 concentration distributions, showed significantly higher O3 concentrations over the whole GSA mainly due to the retarded and slow-moving sea-breeze front under the weak opposing synoptic flow. Modeling study also indicated that local and synoptic meteorological processes play a major role in determining the high O3 concentration distribution patterns over the GSA.