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Longhong, nestled on the northern coast of Hainan Island in China (19.8828° N, 110.4111° E), is a small coastal city with a population of approximately 29,530. Its geography is defined by a relatively flat coastal plain, gently rising inland towards the central mountainous spine of Hainan. This proximity to the South China Sea significantly influences its climate and, consequently, its air quality. The surrounding landscape is a mix of tropical rainforest, agricultural land – primarily rubber and fruit plantations – and increasingly, tourism-related development. Longhong isn’t situated within a major industrial belt, which is a positive factor, but is downwind of larger, more industrialised areas on the mainland during certain wind patterns. The urban-rural gradient is quite sharp; the city centre is densely populated, transitioning rapidly to agricultural fields and forested areas. The coastal location means frequent sea breezes, which can both disperse and transport pollutants. The low elevation contributes to potential temperature inversions, trapping pollutants near the ground. The city’s position makes it vulnerable to seasonal monsoon winds and associated rainfall, impacting pollutant washout. Understanding these geographical factors is crucial for assessing and mitigating air quality challenges in Longhong.

Longhong experiences a tropical monsoon climate, leading to distinct wet and dry seasons that heavily influence air quality. The dry season, roughly from November to April, typically sees poorer air quality. Reduced rainfall means less atmospheric cleansing, and stable high-pressure systems can lead to temperature inversions, trapping pollutants emitted from local traffic, construction, and agricultural burning. January and February are often the months with the least favourable conditions. The wet season, from May to October, brings frequent rainfall and stronger winds, effectively washing pollutants from the atmosphere and improving air quality. However, increased humidity can also promote the formation of secondary pollutants. August and September, coinciding with typhoon season, can experience periods of intense rainfall and wind, offering significant, though temporary, relief. Sensitive groups – children, the elderly, and those with respiratory conditions – should exercise caution during the dry season, limiting strenuous outdoor activity. During the wet season, while air quality is generally better, mould growth due to high humidity can exacerbate respiratory issues. Monitoring weather patterns and local conditions is key to protecting health.