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Caerfyrddin (Carmarthen), nestled in the heart of Carmarthenshire, Wales, occupies a geographically significant position within the Tywi Valley. The town is built around the River Tywi, which flows into Carmarthen Bay, influencing local microclimates and potentially affecting pollutant dispersion. The terrain is gently undulating, rising towards the Brecon Beacons National Park to the east and the Cambrian Mountains to the north, creating a bowl-like effect that can trap air during stable atmospheric conditions. Historically an important market and administrative centre, Caerfyrddin’s urban character is a blend of medieval streets and modern development. While not heavily industrialised, the surrounding agricultural land – predominantly pasture and arable farming – contributes to particulate matter through agricultural practices and ammonia emissions from livestock. The proximity to the coast introduces a maritime influence, with prevailing winds generally from the southwest. The urban-rural gradient is relatively sharp, transitioning quickly to open countryside. This interplay of topography, water bodies, and land use patterns dictates the local air quality dynamics, making Caerfyrddin susceptible to localised pollution events, particularly during periods of calm weather. The town’s location within a valley necessitates careful consideration of pollutant accumulation and dispersion.

Caerfyrddin’s air quality follows a distinct seasonal pattern. Winter (December-February) often sees poorer air quality due to increased reliance on solid fuel heating, leading to elevated particulate matter (PM2.5 and PM10) concentrations, exacerbated by frequent temperature inversions trapping pollutants near ground level. Calm, damp conditions and fog further contribute to this. Spring (March-May) generally brings improvement as temperatures rise and heating demand decreases, though agricultural activities begin to increase ammonia levels. Summer (June-August) typically offers the cleanest air, benefiting from prevailing winds dispersing pollutants and higher temperatures promoting atmospheric mixing. However, occasional heatwaves can lead to ozone formation. Autumn (September-November) sees a gradual decline in air quality as heating use increases again, coupled with agricultural practices like slurry spreading. October and November are often the most challenging months. Sensitive individuals – those with respiratory conditions, the elderly, and young children – should limit strenuous outdoor activity during winter mornings and periods of calm weather. Monitoring local forecasts and avoiding busy roads during peak hours are advisable year-round. The maritime influence moderates extremes, but localised pollution events can still occur.