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Sihanoukville, situated on Cambodia's southwestern coast in Preah Sihanouk province, occupies a strategic position along the Gulf of Thailand in Southeast Asia. The city's geography is characterized by a coastal plain flanked by the Dâmrei Mountains to the northeast, creating a natural amphitheater that influences air circulation patterns. With an elevation generally below 50 meters near the urban core, Sihanoukville's terrain slopes gently toward the sea, featuring numerous bays, beaches, and offshore islands. This port city serves as Cambodia's primary deep-water maritime gateway, with its urban character rapidly transforming from a quiet fishing town to a bustling hub of tourism, construction, and logistics. The surrounding landscape includes mixed agricultural zones producing rice and tropical fruits, though these are increasingly giving way to urban expansion. Proximity to the Gulf of Thailand moderates temperatures but also facilitates maritime emissions from shipping lanes. The urban-rural gradient shows intense development concentrated along the coastline and major roads, with construction dust and vehicle emissions becoming pervasive. Geographic factors specifically affecting air quality include the mountain ranges that can trap pollutants during calm weather, while sea breezes occasionally provide ventilation. The city's position as an economic corridor connecting maritime trade with inland regions means heavy truck traffic contributes significantly to road dust and exhaust emissions year-round.

Sihanoukville's tropical wet-and-dry climate creates distinct seasonal patterns in air quality, driven primarily by monsoon cycles. During the dry season from November to April, pollution typically peaks, with February through April being particularly problematic. These months experience minimal rainfall, allowing construction dust, road dust, and vehicle emissions to accumulate without washout. Northeast monsoon winds bring drier continental air that can transport additional particulates, while frequent temperature inversions trap pollutants near the surface, especially during calm mornings. Sensitive groups should limit outdoor exertion during these months, particularly in high-traffic areas. The wet season from May to October brings relief as southwest monsoon rains effectively scrub pollutants from the air, with June through September showing the cleanest conditions. However, this period presents different challenges: high humidity can combine with emissions to form secondary pollutants, while tropical storms and flooding may temporarily suspend dust but can stir up mold and biological particles. Transitional months of May and October offer moderate conditions, though occasional haze from agricultural burning in neighboring regions may affect visibility. For optimal air quality, visitors should target the early wet season (June-July) when rains are established but not excessive. Year-round, morning hours generally show better dispersion than afternoons when thermal convection slows, and coastal breezes provide some localized cleansing near waterfront areas.