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Hengnan, a county-level city in Guangdong Province, China, occupies a position within the Pearl River Delta, a region renowned for its intensive economic activity and complex environmental challenges. Located at coordinates 22.5348° N, 113.2491° E, Hengnan’s terrain is largely characterized by low-lying plains interspersed with gently rolling hills, typical of the deltaic landscape. The city benefits from proximity to the Pearl River, a vital waterway for transportation and commerce, but this also introduces potential for waterborne pollution impacting local air quality through evaporation and aerosol formation. Surrounding Hengnan are extensive agricultural zones, particularly rice paddies, alongside burgeoning industrial areas concentrated further east towards the major port cities. This urban-rural gradient creates a complex interplay of emissions sources. The Pearl River Delta experiences a subtropical climate, with high humidity and frequent cloud cover, which can trap pollutants. Hengnan’s relatively flat topography limits natural dispersion of emissions, exacerbating air quality issues. The city’s position downwind of larger industrial centres means it frequently receives transported pollutants, contributing to regional air pollution events. Understanding these geographical factors is crucial for effective air quality management in Hengnan.

Hengnan’s air quality follows a distinct seasonal pattern dictated by the region’s subtropical monsoon climate. Winter (November to March) typically sees the poorest air quality. Reduced rainfall and weaker winds allow pollutants from local industry and regional sources to accumulate, often exacerbated by temperature inversions trapping emissions near the ground. January and February are generally the most challenging months. Spring (April-May) brings increased rainfall and gradually improving conditions, though dust storms originating from northern China can occasionally impact visibility and air quality. Summer (June-August) is characterized by the influence of the Southwest Monsoon, bringing cleaner air from the ocean and dispersing pollutants. However, high temperatures and humidity can promote the formation of ozone, a secondary pollutant. Autumn (September-October) offers a transitional period, with generally good air quality until the onset of winter conditions. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during winter months and periods of high ozone concentration in summer. Monitoring weather forecasts and air quality reports is essential for proactive health management.