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Tong’anyi, nestled within Gansu Province in northwestern China, occupies a geographically complex position along the northern fringes of the Loess Plateau. Located at coordinates 35.3041°N, 104.6802°E, the city sits at an elevation of approximately 1,800 meters (5,900 feet), contributing to a cooler, drier climate. The surrounding landscape is characterised by undulating hills and deeply eroded gullies typical of loess terrain, interspersed with agricultural land. The Yellow River flows relatively close to Tong’anyi, though not immediately adjacent, influencing regional humidity patterns. While not a major industrial hub itself, Tong’anyi is situated within a region experiencing increasing industrial activity in larger cities like Lanzhou, impacting downwind air quality. The urban-rural gradient is pronounced; the city centre is relatively compact, quickly transitioning to agricultural fields and sparsely populated rural areas. This proximity to agricultural zones introduces potential for seasonal dust events and the burning of crop residue. The loess soil itself is highly susceptible to wind erosion, exacerbating particulate matter concentrations. Topography funnels winds through the region, potentially trapping pollutants during periods of atmospheric stability. The city’s location within a basin further limits air circulation, increasing the risk of pollution build-up.

Tong’anyi experiences a distinct continental climate, heavily influencing its air quality throughout the year. Spring (March-May) sees a surge in dust storms originating from the Gobi Desert and the Loess Plateau, dramatically increasing particulate matter levels. These storms, coupled with increased agricultural burning as fields are prepared for planting, create the poorest air quality of the year. Summer (June-August) brings some relief, with occasional rainfall washing pollutants from the atmosphere, but high temperatures can also contribute to ozone formation. Autumn (September-November) is generally considered the most pleasant period for air quality, with cooler temperatures and reduced dust activity. However, increased coal burning for heating as temperatures drop can lead to localised pollution spikes. Winter (December-February) is characterised by cold, dry conditions and frequent temperature inversions. These inversions trap pollutants near the ground, leading to prolonged periods of poor air quality, particularly from residential heating sources. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during spring dust storms and winter heating seasons. Monitoring wind direction is crucial; winds from the north and west typically carry higher pollution levels. Months to avoid prolonged outdoor exposure are March-April and December-January.