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Ewell, nestled within the Surrey Hills Area of Outstanding Natural Beauty, occupies a geographically significant position within the Greater London commuter belt. Located approximately 13 miles southwest of Charing Cross, its coordinates (51.3500, -0.2490) place it on gently undulating terrain, part of the North Downs chalk ridge. The landscape surrounding Ewell is a blend of suburban development and pockets of rural charm, characterised by mature woodland, open fields, and the meandering River Wandle, which contributes to localized humidity. Elevation varies subtly, generally ranging from 60 to 120 meters above sea level. This relatively low elevation, combined with the proximity to the London urban area, influences air quality dynamics. While Ewell benefits from some green space buffering, it's not entirely shielded from the impacts of London's industrial and transportation emissions. The urban–rural gradient is gradual; Ewell transitions from a residential suburb to more agricultural land further south, with occasional small-scale farming still present. The North Downs escarpment to the north provides a partial barrier, but prevailing winds often carry pollutants from the capital. The presence of the River Wandle creates microclimates, sometimes trapping pollutants in stagnant air, particularly during periods of low wind. The underlying chalk geology also influences drainage patterns and can affect the dispersion of airborne particles. Overall, Ewell’s geography presents a complex interplay of natural buffers and urban influences on air quality.

Ewell’s air quality experiences a distinct seasonal rhythm, largely dictated by meteorological conditions. Winter months (December-February) often see the poorest air quality, primarily due to temperature inversions. Cold, clear nights lead to a build-up of pollutants near the ground, trapped by a layer of warmer air aloft. This inversion effect is exacerbated by reduced sunlight hours and lower wind speeds, hindering pollutant dispersal. Domestic heating, reliant on gas and oil, contributes significantly to particulate matter during this period. Spring (March-May) brings a gradual improvement as temperatures rise, and wind speeds increase, facilitating better ventilation. However, pollen levels also surge, impacting respiratory health for many residents. Summer (June-August) generally offers the best air quality, with consistent sunshine, higher wind speeds, and reduced domestic heating. Occasional heatwaves can, however, lead to increased ozone formation, a secondary pollutant. Autumn (September-November) presents a transitional period. While wind speeds remain relatively high, cooler temperatures and increased rainfall can lead to damp conditions, trapping pollutants and creating localised fog, particularly in low-lying areas near the River Wandle. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should be particularly cautious during winter inversions and periods of high pollen counts in spring. During autumn fogs, limiting outdoor exertion is advisable. Maintaining indoor air quality through ventilation and air purification can also be beneficial throughout the year, especially during periods of elevated pollution.