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Chaiyo, nestled within Ang Thong Province, Thailand, occupies a geographically significant position on the Gulf of Thailand coast. Its coordinates (14.6488° N, 100.4788° E) place it within a region characterized by a gently sloping coastal plain transitioning into rolling hills and limestone karsts further inland. The city’s terrain is relatively flat, facilitating urban development, but also influencing local air circulation patterns. Chaiyo’s proximity to the Gulf of Thailand introduces a maritime influence, moderating temperatures and contributing to humidity, but also potentially carrying marine aerosols and pollutants from distant sources. The surrounding landscape is a mosaic of rubber plantations, coconut groves, and small-scale agriculture, typical of the region. While Chaiyo itself is a relatively small town with a population of approximately 12,710, it serves as a local hub for the surrounding rural communities. The urban–rural gradient is gradual, with agricultural land quickly giving way to residential areas and limited commercial zones. There are no major industrial belts immediately adjacent to Chaiyo; however, larger industrial areas are present further north within Chonburi Province, potentially impacting air quality through long-range transport of pollutants. The prevailing winds, generally southwesterly during the monsoon season, can carry pollutants from these industrial zones towards Chaiyo. The elevation, averaging around 10 meters above sea level, contributes to a tendency for stagnant air conditions, particularly during periods of reduced wind speed, exacerbating local pollution accumulation.

Chaiyo’s tropical climate dictates a distinct wet and dry season, profoundly influencing its air quality profile. The dry season, typically spanning November to April, often witnesses a noticeable increase in particulate matter. Reduced rainfall and lower humidity during this period contribute to the accumulation of dust and emissions from agricultural burning, a common practice in the surrounding rural areas for land clearing and crop residue disposal. Temperature inversions, where a layer of warm air traps cooler air near the ground, are more frequent during the cooler, drier months, further hindering vertical mixing and concentrating pollutants. The monsoon season, from May to October, brings increased rainfall and higher humidity, naturally cleansing the atmosphere and dispersing pollutants. However, the monsoon also introduces its own challenges; heavy rainfall can lead to flooding, which can resuspend particulate matter and release volatile organic compounds (VOCs) from inundated areas. Fog, particularly prevalent during the transitional months of October and November, can trap pollutants close to the ground, creating localized episodes of reduced visibility and elevated air quality concerns. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during agricultural burning periods (typically January-March). Outdoor activities are generally more favourable during the monsoon months, although vigilance regarding flood-related air quality impacts is advised. The interplay of these meteorological factors creates a dynamic air quality landscape throughout the year in Chaiyo.