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Hương Thủy, nestled within Thừa Thiên-Huế Province in central Vietnam, presents a fascinating interplay of geography and urban development. Situated at coordinates 16.4000, 107.6889, the city occupies a relatively low-lying area, transitioning from the coastal plains inland towards the foothills of the Annamite Range. This terrain significantly influences air quality, as the surrounding hills can trap pollutants during periods of calm weather. The Perfume River (Sông Hương) flows nearby, offering some natural ventilation but also potentially contributing to humidity and localised fog formation, which can exacerbate pollution. Hương Thủy’s population of approximately 95,299 is distributed across a blend of urban and rural areas, with agricultural lands – primarily rice paddies – dominating the surrounding landscape. While not a major industrial hub itself, its proximity to Huế, a larger urban centre with associated industrial activity, means it experiences some degree of regional pollution transport. The urban-rural gradient is pronounced, with air quality generally deteriorating closer to the city centre and transport corridors. The coastal location also means susceptibility to salt spray and marine aerosols, impacting particulate matter composition. Understanding these geographical factors is crucial for assessing and mitigating air pollution challenges in Hương Thủy.

Hương Thủy experiences a distinct tropical monsoon climate, shaping its annual air quality patterns. The dry season, typically from March to August, often sees worsening conditions. Higher temperatures and reduced rainfall lead to increased dust resuspension from agricultural activities and construction, alongside a greater concentration of vehicle emissions. February and March are particularly prone to dry spells, potentially leading to stagnant air. The wet season, from September to February, generally brings improved air quality due to rainfall scavenging pollutants. However, this period is also associated with increased humidity and potential for fungal spore dispersal, impacting respiratory health. October and November, during the peak of the monsoon season, usually offer the cleanest air. Temperature inversions, common during the cooler months, can trap pollutants near ground level, especially in the mornings. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during the dry season and periods of inversion. The northeast monsoon winds, prevalent from December to February, can transport pollutants from regional sources. Monitoring wind direction is key to understanding pollution source contributions.