The overall aim of the project is to develop and demonstrate methods for traceability and calibration of different aerosol instruments capable of covering the environmentally relevant size range from several nm up to 10 μm and the regulatory relevant mass concentrations (0.1 μg/m³ to 1000 μg/m³) and number concentrations (102 to 106 particles per cm³). The traceability and calibration will consider the above metrics as well as mass concentration and chemistry of particle components. The project also aims to provide the necessary EU wide calibration infrastructure for aerosol instruments. The specific objectives of the project are: To develop reproducible reference methods for PM10 and PM2.5, including the design and building of a demonstration aerosol chamber system – for calibrating PM10 and PM2.5 instruments using representative generated aerosols and to achieve target uncertainties below 15 %. To establish traceable validated methods for the determination of major components of particulate matter such as elemental and organic carbon (EC/OC), total carbon, anions and cations and major metals (e.g. arsenic, cadmium, mercury, nickel), in order to meet the data quality objectives of current regulation. To develop calibration procedures for Mobility Particle Size Spectrometers (MPSS) for ambient measurements in the size range up to 1000 nm – in support of standardisation requirements from ISO TC 24 WG 12 and CEN TC 264 WG 32. In addition, to provide calibration facilities for measuring particle number concentration using Condensation Particle Counters (CPCs) in ambient air – as required by the standard FprCEN/TS 16976. To apply mobile x-ray spectroscopy techniques combined within particle sampling techniques for quantifying particle compositions in the field for real time analysis. Results will be corroborated by a backup lab-based reanalysis of samples. To qualify a synchrotron based GIXRF setup as a traceable reference for a quantitative chemical aerosol analysis with mobile and bench top GIXRF instrumentation. Full traceability will be achieved by the use of fabricated micro and nanostructures and subsequently calibration along a complete traceability chain will be described in standard operating procedures (SOP). To facilitate the take up of the technology and measurement infrastructure of the project by the measurement supply chain (accredited laboratories), by standards developing organisations (such as ISO TC 24 and CEN TC 264 and those linked to the EU Air Quality Directive 2008/50/EC) and end users (e.g. Network of National Air Quality Reference Laboratories (AQUILA) and the European Monitoring and Evaluation Programme (EMEP).