This brochure contains six articles which illustrate the way in which researchers in Denmark, Finland, Norway and Sweden are collaborating under the auspices of the Nordic Sea and Air Quality Group to gather information on the harmful particulate air pollution that causes an estimated 9,000 premature deaths in the Nordic countries every year. Their overall aim is to reduce particulate air pollution. Particulate air pollution is a serious and as-yet unresolved problem, which only came to light some years ago. Particulate air pollution is the term for the invisible ultrafine particles from, amongst otherthings, traffic and wood-burning stoves that pollute our urban spaces. For this reason, particulate air pollution is a high-priority issue in the Nordic Environmental Action Plan 2005–2008 – and a problem which the joint Nordic Sea and Air Quality Group is working actively to resolve in both scientific and political terms.