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Dongyuya, nestled within Hunan Province, China, occupies a geographically complex position at coordinates 29.5619°N, 111.0350°E. The city’s terrain is characterised by rolling hills typical of the region, a transition zone between the Hunan Basin and the Luoxiao Mountains. This undulating landscape influences local wind patterns, creating pockets of stagnant air that can exacerbate pollution. Dongyuya’s elevation, approximately 200-300 meters above sea level, contributes to temperature inversions, particularly during the colder months. The city is situated relatively close to the Xiang River, a vital waterway for transportation and irrigation, but also a potential pathway for pollutant dispersal. Surrounding Dongyuya are significant agricultural zones, primarily rice paddies and vegetable farms, alongside emerging industrial areas focused on light manufacturing and processing. The urban-rural gradient is relatively sharp; the city centre is densely populated, while the periphery quickly transitions into agricultural land. This proximity to both agricultural practices (potential ammonia emissions from fertilizers) and industrial activity (particulate matter and sulfur dioxide) directly impacts the city’s air quality. The regional climate, a humid subtropical climate, further complicates air quality management due to high humidity and frequent fog, trapping pollutants near the ground. The city’s location within a basin limits air circulation, increasing the concentration of airborne particles.

Dongyuya experiences a distinct seasonal air quality pattern dictated by its humid subtropical climate. Spring (March-May) sees a rise in pollutants due to increased agricultural activity – fertilizer application and burning of crop residue – combined with relatively calm winds. Dust storms originating from the Gobi Desert can also impact air quality during this period. Summer (June-August) brings the monsoon season, offering periods of cleaner air as rainfall washes away pollutants and stronger winds disperse them. However, high humidity can also promote secondary pollutant formation. Autumn (September-November) is often the most challenging period. Temperatures drop, leading to increased coal burning for heating, and temperature inversions become more frequent, trapping pollutants. November is particularly problematic. Winter (December-February) sees consistently poor air quality due to continued coal use, stagnant air masses, and frequent fog. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during November and December. Periods of strong southerly winds in late winter can briefly improve conditions. Overall, spring and autumn require heightened awareness, while summer offers the most favourable air quality, though even then, ozone levels can be elevated on sunny days.