Ultrafine particles. Some views on preferred metrics

The European Federation of Clean Air and Environmental Protection Associations (EFCA) was founded by European associations in the 90-ies in reaction to the decision to harmonise environmental policies in Europe. EFCA stimulates scientific and professional activity in Europe and, during the last ten years, developed a strategy with priority topics, in line with its mission to connect science and policy 1. In this paper we report on two interrelated priority topics on which we advised the European Commission: BL ""One atmosphere"": the need for integrated policies on clean air and climate BL ""Particulate matter"": the deficiencies in the PM-regulation