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Shizukuishi, nestled in Iwate Prefecture, Japan, presents a unique geographic setting influencing its air quality. Located at 39.6952°N, 140.9758°E, the city occupies a basin surrounded by the Kitakami Mountains, a landscape characterised by rolling hills and forested slopes. The elevation varies, contributing to localized microclimates and potential for temperature inversions. The city is not directly coastal, but benefits from proximity to the Pacific Ocean, approximately 50km east, which moderates temperatures but also introduces maritime air masses. Shizukuishi’s economy is largely agricultural, with rice cultivation dominating the landscape, alongside some forestry. Unlike many Japanese cities, it lacks a significant industrial belt within its immediate boundaries, which is a positive factor for baseline air quality. The urban-rural gradient is pronounced; the city centre is relatively compact, quickly transitioning to rural farmland and mountainous terrain. This rapid change impacts air dispersion patterns, with pollutants potentially accumulating in the basin during stable atmospheric conditions. The surrounding mountains act as barriers to airflow, influencing the movement of air masses and the dilution of pollutants. Understanding these geographical factors is crucial for interpreting local air quality trends.

Shizukuishi’s air quality follows a distinct seasonal pattern. Spring (March-May) sees an increase in particulate matter from agricultural burning as farmers prepare fields for planting, coupled with pollen from deciduous trees. Winds are often changeable, sometimes trapping pollutants in the basin. Summer (June-August) generally offers the cleanest air, benefiting from monsoon winds that flush out accumulated pollutants and increased rainfall that scavenges particles. However, high humidity can contribute to secondary pollutant formation. Autumn (September-November) brings clearer skies initially, but as temperatures drop, stable atmospheric conditions become more frequent, leading to temperature inversions that trap pollutants near the ground, particularly in the mornings. November often sees increased wood smoke from heating. Winter (December-February) is typically the most challenging period. Siberian air masses bring cold, dry air and frequent temperature inversions, trapping pollutants from heating sources. Snowfall can temporarily improve air quality by settling particles, but melting snow releases them again. Sensitive individuals – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during autumn and winter mornings. Monitoring wind direction and avoiding activity near agricultural areas during spring burning is also advisable.