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Dongshan Township, nestled within Yilan County in northeastern Taiwan, presents a unique geographic setting influencing its air quality. Situated at coordinates 24.6319, 121.7539, the township occupies a relatively low-lying area between the Central Mountain Range and the Pacific Ocean. This positioning creates a funnel effect, potentially trapping pollutants during periods of stagnant air. The terrain is predominantly plains, transitioning to foothills as one moves westward towards the mountains. The Lanyang River, a significant waterway, flows nearby, offering some natural ventilation but also contributing to humidity which can exacerbate pollutant formation. Dongshan is largely rural, characterized by agricultural lands – particularly rice paddies and fruit orchards – with a developing urban core around the township office. Unlike heavily industrialized western Taiwan, Yilan County maintains a stronger agricultural focus, reducing direct industrial emissions within Dongshan itself. However, prevailing easterly winds can transport pollutants from the industrial zones of Hualien County to the south and the Taipei metropolitan area to the northwest, impacting Dongshan’s air. The urban-rural gradient is noticeable, with air quality generally better in the more open agricultural areas compared to the township center. The population of 53,235 contributes to localized emissions from transportation and residential heating.

Dongshan’s air quality follows a distinct seasonal pattern dictated by Taiwan’s subtropical monsoon climate. Spring (March-May) often sees increased particulate matter from agricultural burning and dust storms originating from mainland China, carried by the prevailing winds. Humidity rises, potentially forming fog that traps pollutants near the ground. Summer (June-August) brings the southwest monsoon, offering periods of cleaner air due to increased rainfall and wind dispersal, though high temperatures can promote ozone formation. Typhoons, common during this season, can temporarily improve air quality through heavy rainfall but also disrupt transportation and potentially release pollutants from damaged infrastructure. Autumn (September-November) is generally the most favourable period, with stable high-pressure systems bringing clear skies and moderate temperatures. However, temperature inversions can occur, trapping pollutants in the lower atmosphere. Winter (December-February) experiences the northeast monsoon, bringing colder, drier air and often stagnant conditions. This leads to a build-up of pollutants, particularly particulate matter, making it the season with the poorest air quality. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during winter mornings and periods of stagnant air. Monitoring wind direction and avoiding exercise near roadways are recommended year-round.