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Sanya occupies a distinctive geographical position at the southernmost tip of Hainan Island, China's tropical southern province, where the South China Sea meets the Gulf of Tonkin. This coastal city, often dubbed 'China's Hawaii,' is characterized by a narrow coastal plain backed by lush, forested hills and mountains, including the Wuzhi Mountain range to the north, which rises to over 1,800 meters. The urban core clusters along Sanya Bay, Yalong Bay, and Haitang Bay, with development sprawling inland along river valleys. Sanya's geography profoundly influences its air quality: its island setting and sea breezes from the surrounding waters typically disperse pollutants efficiently, resulting in generally good air quality compared to mainland Chinese cities. However, the city's rapid urban growth—transforming from a fishing village to a major tourist hub—has introduced pollution sources like vehicle emissions, construction dust, and energy generation for tourism infrastructure. The surrounding landscape includes agricultural zones producing tropical fruits and rubber, which can contribute biogenic emissions, though these are minimal. The urban–rural gradient shows cleaner air in less developed eastern and northern areas, while the downtown and port regions experience higher particulate matter. Proximity to Southeast Asia means occasional transboundary haze from regional agricultural burning, but Sanya's coastal winds usually mitigate this impact.

Sanya's air quality follows a distinct seasonal pattern shaped by its tropical monsoon climate, with pollution levels generally low but fluctuating due to meteorological factors. In winter (December to February), the northeast monsoon brings cool, dry winds from mainland China, which can occasionally carry pollutants from industrial regions, leading to slight increases in particulate matter; however, sea breezes often dilute these, making this season favourable for outdoor activities. Spring (March to May) sees transitional weather with rising temperatures and humidity, potentially trapping local emissions like vehicle exhaust under light winds, but frequent rainfall helps cleanse the air. Summer (June to August) is dominated by the southwest monsoon, bringing heavy rains and strong oceanic winds that vigorously disperse pollutants, resulting in the cleanest air of the year—ideal for sensitive groups such as asthmatics to enjoy outdoor pursuits. Autumn (September to November) marks a return to drier conditions, with reduced rainfall sometimes allowing dust from construction sites to accumulate, though tropical storms can provide intermittent cleansing. Throughout the year, temperature inversions are rare due to the coastal setting, but fog can occur in early mornings, temporarily elevating moisture-related pollutants. Health guidance for sensitive individuals: avoid strenuous activities during occasional haze episodes in winter, and monitor local forecasts during transitional seasons when pollution may peak subtly.