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Ji’an City, nestled within the northeastern province of Jilin, China, occupies a geographically significant position along the Yalu River, bordering North Korea. Located at coordinates 41.1253°N, 126.1940°E, the city’s terrain is characterised by a mix of mountainous landscapes and river valleys. The surrounding area is dominated by the Changbai Mountains to the east, contributing to a complex topography that influences local wind patterns and pollutant dispersion. Ji’an’s elevation varies, but generally sits between 150-300 meters above sea level. The Yalu River acts as a crucial hydrological feature, but also a potential pathway for transboundary pollution. Historically, Ji’an served as a vital trading post, and while industry has developed, a substantial portion of the surrounding land remains agricultural, primarily focused on grain and forestry. The urban-rural gradient is relatively sharp, with the city centre concentrated along the river, transitioning quickly to forested hills and farmland. This proximity to both natural landscapes and potential pollution sources – from local industry and seasonal agricultural burning – creates a unique air quality profile. The city’s location within a river valley can exacerbate pollution events through temperature inversions, trapping pollutants near the ground.

Ji’an experiences a distinct four-season climate, profoundly impacting its air quality. Spring (March-May) sees increasing temperatures and winds, initially dispersing winter pollutants, but also bringing dust storms from the Gobi Desert, impacting particulate matter levels. Summer (June-August) is generally the cleanest period, with monsoon rains effectively washing away pollutants and higher temperatures promoting atmospheric mixing. However, localised thunderstorms can temporarily stir up dust. Autumn (September-November) is often marked by a deterioration in air quality. Stagnant high-pressure systems become dominant, leading to temperature inversions that trap pollutants, particularly from residential coal burning for heating. Agricultural burning of crop residue also contributes to increased particulate matter. Winter (December-February) is the most challenging season. Cold temperatures increase coal consumption for heating, and frequent temperature inversions exacerbate pollution build-up. Snowfall can temporarily improve conditions, but also reflects pollutants, increasing their concentration. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during autumn and winter. Spring can also pose risks due to dust. Monitoring wind direction and avoiding peak heating hours are advisable.