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Leiyang is a county-level city in southern Hunan Province, situated within the Xiang River basin approximately 150 kilometers south of Changsha. The city occupies a transitional zone between the Nanling Mountains to the south and the rolling hills of central Hunan, creating a basin-like topography that significantly influences its air quality patterns. At an elevation of around 100-200 meters above sea level, Leiyang lies in the middle reaches of the Lei River, a tributary of the Xiang River, with water bodies providing some natural ventilation but also contributing to humidity that can trap pollutants. The urban core, home to over 1.1 million residents, represents a dense urban fabric surrounded by agricultural hinterlands where rice paddies and vegetable farming dominate, creating a distinct urban-rural gradient. This setting places Leiyang within Hunan's industrial corridor, where manufacturing and small-scale industries contribute to general urban pollution sources. The surrounding terrain, characterized by low hills and valleys, can act as a natural barrier to wind dispersion, particularly during stagnant weather conditions. Proximity to major transportation routes, including highways connecting to Guangdong Province, adds vehicular emissions to the pollution mix. The city's location in East Asia's monsoon belt means it experiences seasonal wind patterns that alternately bring cleaner air from the south or polluted air masses from industrialized regions to the north, making its air quality highly dependent on regional atmospheric circulation.

Leiyang's air quality follows a distinct seasonal rhythm shaped by East Asian monsoons and local meteorological conditions. During winter (December-February), cold, dry air from the north often brings temperature inversions that trap pollutants near the surface, creating persistent haze episodes—this is typically the worst period for air quality, with January and February being months sensitive groups should limit prolonged outdoor exposure. Spring (March-May) sees gradual improvement as increasing temperatures and occasional rainfall help disperse pollutants, though March can still experience lingering winter stagnation. The summer monsoon (June-August) brings southerly winds from the South China Sea, which generally usher in cleaner air and higher precipitation that scrubs pollutants from the atmosphere, making summer the most favorable season for outdoor activities despite high humidity. Autumn (September-November) begins with relatively good air quality in September but transitions to worsening conditions as monsoon winds weaken and temperature inversions become more frequent by late October and November. Throughout the year, calm wind conditions and radiation fog, common in the basin topography, can exacerbate pollution buildup regardless of season. Sensitive groups including children, elderly, and those with respiratory conditions should monitor daily air quality reports, use air purifiers indoors during peak pollution periods, and schedule outdoor activities for midday when mixing heights are highest.