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Shanliang, nestled on the northern coast of Hainan Island in China (19.8798°N, 110.6011°E), is a small coastal city with a population of approximately 14,147. Its geography is defined by its proximity to the Qiongzhou Strait, separating Hainan from Guangdong province. The terrain is relatively flat, typical of the coastal plains of northern Hainan, with a gentle slope rising inland towards the central mountainous spine of the island. This low elevation makes Shanliang particularly vulnerable to marine influences and potential pollutant trapping. The surrounding landscape is a mix of coconut groves, agricultural land – primarily rubber and tropical fruit plantations – and increasingly, tourism-related development. While not a major industrial hub itself, Shanliang’s location downwind of larger industrial zones on the mainland and in other parts of Hainan means it can experience transboundary pollution. The urban-rural gradient is quite sharp; the city centre is densely populated, but quickly transitions to rural agricultural areas. The coastal location brings sea breezes, but also the potential for salt spray and humidity, impacting pollutant dispersion. The prevailing winds, influenced by the East Asian monsoon, play a crucial role in air quality, carrying pollutants from regional sources.

Shanliang experiences a tropical monsoon climate, resulting in distinct wet and dry seasons rather than traditional four seasons. Air quality generally improves during the wet season (May to October) due to frequent rainfall which effectively washes particulate matter from the atmosphere. However, high humidity can also promote the formation of secondary pollutants. The driest months, November to April, typically see poorer air quality. The northeast monsoon during winter brings cooler, drier air from the mainland, often carrying pollutants across the Qiongzhou Strait. Temperature inversions, common during calm winter mornings, can trap pollutants near the ground, exacerbating conditions. Fog is also prevalent during these months, further reducing visibility and potentially increasing pollutant concentrations. March and April are often the worst months for air quality due to dust storms originating from the Gobi Desert and the build-up of pollutants from winter emissions. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during these periods. Conversely, the wetter months, particularly July and August, generally offer the best air quality for outdoor pursuits, though precautions against humidity and potential flooding are necessary.