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Cam Ranh, located in Khánh Hòa province, Vietnam, occupies a strategically important coastal position on the South Central Coast. Its coordinates (11.9020° N, 109.2207° E) place it on a narrow peninsula extending into the East Sea (South China Sea), creating a unique microclimate and influencing its air quality dynamics. The city’s terrain is predominantly flat, transitioning to gently rolling hills inland, a characteristic of the coastal plains of this region. This flatness, while facilitating urban development, can also contribute to the trapping of pollutants, particularly during periods of low wind. Cam Ranh Bay, a significant natural harbor, dominates the landscape and influences local weather patterns, often moderating temperatures but also potentially contributing to humidity and fog formation. The surrounding landscape is a mix of agricultural land – primarily rice paddies and aquaculture farms – and mangrove forests along the coastline, which act as natural buffers but can also be sources of localized emissions. To the west, the urban–rural gradient shifts relatively quickly to more rural agricultural areas. Further inland, the landscape rises towards the Trường Sơn mountain range, impacting regional wind patterns and potentially influencing the transport of pollutants. The proximity to industrial zones in Nha Trang, approximately 50km north, means Cam Ranh can experience downwind impacts from industrial emissions, although the distance and prevailing winds often mitigate this effect. The city’s coastal location and relatively low elevation (generally below 30 meters) make it susceptible to sea breezes and coastal fog, which can significantly affect air dispersion.

Cam Ranh experiences a tropical monsoon climate, characterized by distinct wet and dry seasons rather than four traditional seasons. The dry season, typically running from February to August, generally sees improved air quality due to increased wind speeds and drier conditions. These winds, often originating from the northwest, help disperse pollutants more effectively. However, even during the dry season, localized pollution from agricultural burning (preparing fields for planting) and vehicle emissions can occur. The wet season, from September to January, brings increased rainfall and higher humidity. While the rain helps to cleanse the air, the increased humidity can trap pollutants closer to the ground, particularly during periods of reduced wind. Fog, common during the wet season, further exacerbates this issue, significantly reducing visibility and increasing the concentration of particulate matter. Temperature inversions, where a layer of warm air sits above cooler air near the ground, are less frequent than in more temperate climates but can still occur, trapping pollutants and leading to periods of poorer air quality. Months like November and December, coinciding with the peak of the wet season and frequent fog, are generally periods to exercise caution for those with respiratory sensitivities. During the dry season, particularly March to May, outdoor activities are generally more favorable. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should monitor local conditions and limit prolonged outdoor exposure during periods of fog or reduced wind, regardless of the season.