Portsmouth is one of the UK's most densely populated island cities, and its geography only enhances its air quality problem. Traffic is funnelled through a limited number of arterial routes on Portsea Island, while the Portsmouth International Port generates a constant flow of HGVs, coaches, and ferries that define the city's waterfront. The problem is severe enough that Portsmouth was identified by the UK government for exceeding legal pollution limits — forcing the introduction of a Clean Air Zone in 2021. Even so, some locations in the city still exceed the legal limit for nitrogen dioxide, with many more on the edge of breaching it. 

Much of that pollution doesn't stay outside. It infiltrates offices, schools, retail units, and commercial premises throughout the city, mixing with indoor-generated contaminants like VOCs, mould spores, and elevated CO₂ to create an indoor air quality (IAQ) problem that most building owners and managers aren't even aware they have.