Air pollution is thought to be an environmental factor in the development of childhood leukaemia, in addition to known causal relationships with cardiovascular and respiratory disease and heritable DNA damage. The submicron (PM₁) and ultrafine (UFP) fraction of particulate air pollution could play a major role (Oberdörster et al, 2005) due to their higher specific surface area (SA per unit mass of particles). There is also the potential for placental transfer of UFP to the foetus.

Knowledge of submicron particle concentrations and size distributions in exposure situations is important for determining the expected dose to the lung upon inhalation and onward toxicological effects. Current legislation for particulate air pollution is mainly concerned with PM₁₀ and PM_2.5 (particles of sizes up to 10 µm and 2.5 µm respectively). For example, the UK network of monitoring stations which routinely measure PM₁₀ and PM_2.5 (operated by AEA Energy & Environment) do not currently include PM₁ as a measurement parameter. While linked with health problems in their own right, measurements of these quantities do not reflect the much greater number of smaller particles present in most urban atmospheres. There is also the known problem with extrapolating fixed-site measurements to provide an accurate estimate of personal exposure.