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Chepstow, nestled in Monmouthshire, Wales, occupies a strategically significant location at the confluence of the River Wye and the River Severn. This historic market town, with a population of approximately 11,969, is defined by its undulating terrain, rising gently from the riverbanks towards the wooded hills of the surrounding countryside. Its coordinates (51.6420, -2.6750) place it within a temperate maritime climate, heavily influenced by the proximity to the Bristol Channel. Historically, Chepstow’s development was intrinsically linked to its river access, serving as a vital port and a crossing point. While no longer a major industrial hub, the town benefits from transport links to larger industrial areas in South Wales and the West of England. The surrounding landscape is a mosaic of agricultural land – predominantly pasture – and deciduous woodland. The urban-rural gradient is relatively sharp, with farmland immediately bordering the town’s periphery. This proximity to agricultural activity introduces potential sources of particulate matter from farming operations. The river estuaries, while providing natural ventilation, can also trap pollutants during calm weather conditions, impacting localised air quality. The town’s position within a valley also contributes to potential temperature inversions, exacerbating pollution episodes.

Chepstow’s air quality follows a distinct seasonal pattern. Winter (December-February) typically sees the poorest air quality, driven by increased reliance on solid fuel heating and stagnant atmospheric conditions. Temperature inversions, common in the valley location, trap pollutants close to the ground, leading to higher concentrations of particulate matter. Fog, frequent during these months, further exacerbates the issue. Spring (March-May) brings improvement as temperatures rise and wind speeds increase, dispersing pollutants. However, agricultural activities, such as fertiliser application, can contribute to ammonia levels. Summer (June-August) generally offers the cleanest air, with prevailing winds flushing out pollutants and higher temperatures promoting dispersion. However, occasional heatwaves can lead to increased ozone formation. Autumn (September-November) sees a gradual decline in air quality as heating demand increases and atmospheric stability returns. October and November are often marked by damp, still conditions, trapping pollutants. Sensitive individuals – those with respiratory conditions, the elderly, and young children – should be particularly cautious during winter and early spring. Avoiding strenuous outdoor activity on high pollution days and monitoring local forecasts are recommended. Periods of strong westerly winds in spring and summer are generally favourable for outdoor activity.