## 1 Introduction  
Fine particulate matter (PM) refers to airborne or suspended particles that can have serious health impacts depending on their size [1, 2]. PM is particularly harmful as it can cause respiratory and cardiovascular diseases, posing a significant threat to vulnerable populations such as children, older adults, and individuals with chronic illnesses [3, 4]. This study combines environmental health, which examines the health impacts of air pollution, with urban planning and spatial analysis using geographic information systems (GIS), and social welfare, which aims to improve the quality of life for vulnerable populations [5, 6]. Given these health risks, fine PM has gained global attention as a critical social challenge [7]. In major South Korean cities, including Seoul and its surrounding areas, frequent PM alerts significantly affect residents' health and daily lives [8]. Although various technological systems measure and provide real-time PM concentrations, research is limited on how well these systems meet the needs of vulnerable populations. Additionally, disparities persist in access to PM information between areas where vulnerable populations reside and the facilities they frequently use [9]. Recent studies have highlighted that PM in Seoul and nearby areas originates from various sources, including vehicular emissions, industrial activities, and secondary aerosol formation from chemical reactions in the atmosphere [10, 11, 12]. These sources contribute significantly to the regional PM concentration and affect both visibility and health outcomes. For example, high levels of sulfate and nitrate have been associated with decreased visibility in urban areas, as well as with adverse health effects, including increased cardiovascular and respiratory mortality [10; 12]. In the Seoul Metropolitan Area, PM levels have shown fluctuations influenced by both seasonal meteorological factors and human activities, with a notable increase in PM episodes related to stagnant weather conditions and reduced ventilation [11]. Understanding these sources and their impact on health is essential for developing effective PM monitoring and mitigation strategies. Despite the availability of real-time PM monitoring systems, there is a gap in research on how effectively these systems address the specific needs of vulnerable populations in terms of accessibility and timeliness. Furthermore, there are still significant disparities in access to air quality information in different regions, particularly in areas where vulnerable groups live. This study seeks to fill this gap by analyzing the spatial distribution of vulnerable populations and proposing optimal locations for PM alert systems. The key research questions this paper addresses are (1) how can PM alert systems be strategically placed to better serve vulnerable populations? And (2) what factors should be considered to ensure equitable access to air quality information across different areas? Gangeo District, located in western Seoul, faces significant environmental challenges due to its proximity to Incheon International Airport and industrial zones. Air pollution from vehicular emissions, industrial activities, and construction contributes to high levels of PM2.5 and PM10, posing health risks to local residents, especially the elderly and children. The urban heat island effect worsens air quality by trapping pollutants, making it critical to address these issues to protect public health. Gangeo District experiences a humid continental climate with four distinct seasons. Summers are hot and humid, while winters are cold and dry. In particular, fine dust levels rise during the spring due to yellow dust storms. These seasonal variations in air quality highlight the need for an effective fine dust monitoring system to protect vulnerable populations. This study aimed to identify the residential distribution and related facilities of vulnerable populations in Gangeo District to propose optimal locations for PM alert systems.