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Ninh Hòa, a coastal city in Khánh Hòa Province, Vietnam, occupies a geographically significant position in south-central Vietnam. Situated at coordinates 12.4917°N, 109.1258°E, the city benefits from a relatively flat coastal plain, gently rising towards the Truong Son mountain range to the west. This terrain influences air circulation patterns, potentially trapping pollutants during periods of calm weather. The city’s proximity to Nha Phu Bay and the South China Sea introduces maritime influences, including sea breezes that can both disperse and, at times, concentrate pollutants depending on prevailing wind directions. Ninh Hòa is surrounded by a mix of agricultural land – primarily rice paddies and fruit orchards – and emerging industrial activity focused on processing agricultural products and light manufacturing. The urban-rural gradient is pronounced, with denser development concentrated along the coastal road and around the city center, transitioning to more dispersed settlements and agricultural areas further inland. This gradient impacts air quality, as industrial and traffic emissions are concentrated in urban zones, while agricultural practices contribute to particulate matter and ammonia. The city’s location within a monsoon climate zone further complicates air quality dynamics, with seasonal shifts in wind patterns and rainfall influencing pollutant dispersion and removal. Understanding these geographical factors is crucial for effective air quality management in Ninh Hòa.

Ninh Hòa experiences a distinct wet and dry season, heavily influencing its air quality. The dry season, typically from January to August, sees consistently higher pollution levels. This is due to reduced rainfall, meaning less atmospheric cleansing, and stronger, more consistent winds carrying pollutants from regional sources. February and March are often the most challenging months, with agricultural burning practices contributing to increased particulate matter. The wet season, from September to December, brings significant improvements in air quality. Heavy rainfall effectively washes pollutants from the atmosphere, and increased humidity can suppress dust. However, the wet season also brings the risk of localised flooding, which can mobilise pollutants from contaminated areas. Temperature inversions, common during the calmer periods of the dry season, exacerbate pollution by trapping emissions near the ground. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during the dry season, particularly in February and March. Monitoring wind direction is also important, as pollutants can be transported from nearby industrial areas. Overall, the wet season offers a reprieve, making September to November the most favourable months for outdoor activities.