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Zhongnan, nestled within the southern province of Hainan, China, occupies a geographically unique position on the island’s western coast. Located at approximately 19.1476° N, 110.4695° E, the city’s terrain is characterized by a gradual transition from coastal plains to gently sloping hills, reflecting the island’s volcanic origins. The surrounding landscape is dominated by lush tropical rainforest, interspersed with agricultural lands primarily dedicated to fruit cultivation, notably lychee and mango. Zhongnan’s proximity to the South China Sea significantly influences its climate and, consequently, its air quality. The prevailing sea breezes generally provide a natural ventilation effect, dispersing pollutants, but can also carry maritime aerosols. The urban character of Zhongnan is relatively small-scale, reflecting its modest population of 26,886. It exhibits a clear urban-rural gradient, with denser residential and commercial areas concentrated closer to the coastline, gradually giving way to agricultural fields and forested areas further inland. While not directly adjacent to major industrial belts, Hainan’s broader economic development, including tourism and resource extraction, can indirectly impact air quality through transportation emissions and potential industrial runoff. The elevation is relatively low, rarely exceeding 100 meters above sea level, which can exacerbate temperature inversions under certain meteorological conditions, trapping pollutants near the ground. The island’s overall isolation, while beneficial in some respects, also limits the dispersal of pollutants from external sources.

Hainan’s tropical climate dictates a wet and dry season pattern, profoundly influencing Zhongnan’s air quality. The wet season, typically spanning from May to October, brings frequent rainfall and high humidity, naturally cleansing the atmosphere and significantly reducing particulate matter. Monsoon winds during this period also contribute to pollutant dispersal, generally resulting in improved air quality. Conversely, the dry season (November to April) presents a greater challenge. Reduced rainfall, coupled with lower humidity, allows pollutants to accumulate. Temperature inversions, common during the cooler months of December and January, trap cooler air near the ground, preventing vertical mixing and concentrating pollutants. Fog, particularly prevalent in the mornings during the dry season, further restricts visibility and exacerbates the impact of pollutants. Agricultural burning, a traditional practice for land clearing and crop residue disposal, can also contribute to localized air pollution spikes during the transition periods between seasons. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly on days with fog or temperature inversions. Outdoor activities are generally more favorable during the wet season, although heavy rainfall can still impact visibility and safety. The interplay of these meteorological factors creates a dynamic air quality profile, demanding adaptive strategies for public health and environmental management.