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Chichester, a historic cathedral city in West Sussex, occupies a unique geographic position within the South Downs National Park, significantly influencing its air quality profile. Situated at the northern edge of the park, the city’s terrain is gently undulating, transitioning from the coastal plain towards the steeper slopes of the Downs. Its coordinates (50.8365, -0.7792) place it approximately 8 miles inland from Chichester Harbour, a complex estuarine system and Ramsar site. This proximity to the coast introduces a maritime influence, generally moderating temperatures and increasing humidity, but also potentially carrying in pollutants from shipping activity and coastal industrial areas further east. The surrounding landscape is predominantly agricultural, with arable fields and pastureland dominating the rural areas, which can contribute to particulate matter through farming practices, particularly during harvest seasons. While Chichester itself is relatively small, it sits within a wider commuter belt, experiencing traffic flow from surrounding towns and villages, and is connected to larger urban centres like Portsmouth and Brighton. The urban–rural gradient is gradual, with smaller settlements and dispersed rural properties bordering the city, meaning that localised pollution sources can have a more immediate impact. The city’s elevation, averaging around 150 feet above sea level, combined with the prevailing southwesterly winds, generally facilitates the dispersion of pollutants, though temperature inversions, common during winter months, can trap pollutants closer to the ground. The absence of major heavy industry within Chichester itself is a mitigating factor, but regional industrial zones contribute to background pollution levels.

Chichester’s air quality experiences a distinct seasonal pattern dictated by meteorological conditions. Winter months (December-February) often present the greatest challenges. Temperature inversions, where a layer of warm air sits above cooler air near the ground, are frequent, trapping pollutants and leading to stagnant air conditions. Fog, common during this period, exacerbates the issue by reducing visibility and further hindering dispersion. Agricultural activities, including the spreading of manure, can also contribute to ammonia emissions, impacting local air quality. Spring (March-May) typically sees an improvement as winds increase and temperatures rise, dispersing pollutants more effectively. However, pollen levels surge, impacting those with respiratory sensitivities. Summer (June-August) generally offers the best air quality, with consistent breezes and warm temperatures promoting good ventilation. Agricultural activity slows down, reducing emissions. Autumn (September-November) marks a transitional period. While winds remain relatively strong, the return of cooler temperatures can occasionally trigger localised inversions, particularly in the evenings. The harvest season can also lead to increased dust and particulate matter. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions like asthma, should be particularly mindful during winter months, limiting prolonged outdoor exposure on days with poor visibility or reported stagnant air. During pollen season, those with allergies should monitor pollen forecasts and take appropriate precautions. Maintaining awareness of regional air quality alerts and adhering to public health guidance is crucial for minimising exposure throughout the year.