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Kuriyama, nestled in the heart of Hokkaido, Japan, presents a unique geographic setting influencing its air quality. Located at 43.0500°N, 141.7833°E, the city occupies a relatively flat, inland portion of the Ishikari Plain. This plain, formed by alluvial deposits from the Ishikari River, is surrounded by low mountains, creating a basin-like topography. The terrain is predominantly agricultural, with extensive rice paddies and farmlands dominating the landscape. Kuriyama’s elevation is modest, around 30-50 meters above sea level, contributing to stable atmospheric conditions. The city isn’t directly adjacent to the coast, but benefits from the moderating influence of the Sea of Japan, though this influence is lessened by the intervening landmass. While not a major industrial hub, Kuriyama supports food processing and agricultural machinery industries, contributing to localised emissions. The urban-rural gradient is sharp; the city centre is compact, quickly transitioning to expansive agricultural areas. This proximity to agricultural practices, including seasonal burning of rice straw, significantly impacts local air quality. The surrounding mountains can trap pollutants during temperature inversions, exacerbating air quality issues, particularly during colder months. The prevailing winds, generally from the northwest, can transport pollutants from other parts of Hokkaido, adding to the complexity of Kuriyama’s air quality profile.

Kuriyama’s air quality follows a distinct seasonal pattern, heavily influenced by Hokkaido’s climate. Spring (March-May) sees a gradual improvement as snowmelt reduces particulate matter, but agricultural burning begins, introducing smoke and organic compounds. Summer (June-August) generally offers the cleanest air, with prevailing winds dispersing pollutants and rainfall acting as a natural scrubber. However, increased humidity can contribute to the formation of secondary pollutants. Autumn (September-November) is often the most challenging period. The harvest season brings widespread agricultural burning, releasing significant amounts of PM2.5 and other pollutants. Temperature inversions become more frequent as temperatures drop, trapping pollutants near the ground. Winter (December-February) is characterised by cold, dry air and stable atmospheric conditions. Snowfall can temporarily improve air quality by scavenging pollutants, but also creates icy road conditions, increasing vehicle emissions. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during autumn and winter. Fog, common in winter, can exacerbate respiratory issues. Monitoring wind direction is crucial; winds from the northwest may carry pollutants from regional sources. Avoiding outdoor exercise during peak burning periods in autumn is advisable.