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Heyuan is a prefecture-level city in northern Guangdong Province, situated at the confluence of the Dong River and its tributaries within the Pearl River Basin. Its coordinates place it approximately 150 kilometers northeast of Guangzhou, positioning it at the transitional zone between the densely populated Pearl River Delta to the south and the mountainous regions of northern Guangdong. The city's terrain is predominantly hilly, with elevations ranging from 50 to 1,000 meters above sea level, creating a varied landscape that includes river valleys and forested uplands. This topography influences local air circulation patterns, with valleys potentially trapping pollutants under certain meteorological conditions. Heyuan lies within the Dongjiang River Basin, with the Xinfengjiang Reservoir—one of Guangdong's largest—located nearby, providing both water resources and some moderating effects on local climate. The region represents an urban-rural gradient, with Heyuan City proper serving as an administrative and economic center surrounded by agricultural zones producing rice, fruits, and tea. While not part of Guangdong's primary industrial belt, Heyuan has developed manufacturing sectors including electronics, machinery, and food processing, contributing to urban emissions. The city's location inland from the coast means it lacks the direct maritime ventilation experienced by coastal cities, potentially allowing pollutants to accumulate during stagnant weather conditions. Surrounding forested areas provide some natural air filtration, but the urban core's growing population and transportation network create typical urban pollution sources.

Heyuan experiences a humid subtropical climate with distinct seasonal variations that significantly influence air quality patterns throughout the year. During winter (December-February), cooler temperatures and frequent temperature inversions in the river valleys can trap pollutants near the surface, leading to periods of poorer air quality, particularly during calm wind conditions. This season often sees the highest pollution concentrations, making late winter the least favorable time for outdoor activities, especially for sensitive groups like children, elderly residents, and those with respiratory conditions. Spring (March-May) brings increasing rainfall and the onset of the southeast monsoon, which helps disperse pollutants through enhanced ventilation, though occasional foggy conditions in early spring can temporarily reduce visibility. Summer (June-August) features the strongest monsoon winds and frequent precipitation, creating the cleanest air conditions of the year as rains wash particulate matter from the atmosphere and consistent winds prevent pollutant accumulation. Autumn (September-November) begins with relatively good air quality but transitions to more stagnant conditions as monsoon winds weaken, with late autumn sometimes experiencing pollution buildup similar to early winter patterns. Sensitive individuals should monitor local air quality reports particularly during winter months and limit prolonged outdoor exertion during periods of reduced air quality, while the summer months generally offer the most favorable conditions for outdoor activities.