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Kỳ Anh, nestled in Hà Tĩnh Province, Vietnam, occupies a crucial coastal position at coordinates 18.0678°N, 106.2967°E. The city’s geography is defined by a relatively flat coastal plain, gradually rising towards the western foothills of the Annamese Range. This terrain significantly influences air quality, as the mountains can trap pollutants during periods of calm weather, creating localised build-ups. The city fronts onto the South China Sea, benefiting from coastal breezes that can, at times, disperse pollutants, but also susceptible to maritime influences on humidity and fog formation. Kỳ Anh is a developing urban centre, experiencing growth linked to the nearby Vũng Áng deep-sea port and associated heavy industries. This industrial belt, a major economic driver for the region, is a key source of potential air pollution. Surrounding the urban core are extensive agricultural lands, primarily rice paddies, which contribute to seasonal biomass burning. The urban-rural gradient is pronounced, with air quality generally deteriorating closer to industrial zones and the city centre, and improving with distance towards agricultural areas and the mountains. The city’s location within a monsoon climate zone further complicates air quality patterns, with distinct wet and dry seasons impacting pollutant dispersion.

Kỳ Anh’s air quality follows a distinct seasonal pattern dictated by the monsoon climate. The dry season, typically from November to April, sees consistently higher pollution levels. Reduced rainfall means less atmospheric cleansing, and stable atmospheric conditions, often with temperature inversions, trap pollutants emitted from industrial activities and biomass burning. February and March are often the most challenging months for respiratory health. The onset of the wet season, around May, brings a significant improvement. Heavy rainfall effectively washes pollutants from the air, and increased humidity aids in particle deposition. However, localised flooding can exacerbate mould growth, impacting indoor air quality. The summer months (June-August) experience relatively clean air, though high humidity can contribute to discomfort. Autumn (September-October) sees a transition period, with increasing dryness and a gradual return of pollution. During the monsoon season, strong winds can occasionally bring in pollutants from other regions. Sensitive groups – children, the elderly, and those with pre-existing respiratory conditions – should limit outdoor activity during the dry season and monitor local conditions closely. Fog, common in the cooler months, can also trap pollutants near ground level.