Air pollution is an environmental and social issue; air pollutants come from both anthropogenic and natural sources and give rise to health and climate change concerns. Accurate aerosol metrology i.e. dimensional quantification and chemical analysis, is a prerequisite for enforcing regulations, protecting human health, and supporting research on climate change and atmospheric processes. However, air pollution is a complex metrology challenge that currently lacks traceable measurement and characterisation of aerosols in the environment. To address this, this project will provide methodological improvements, including calibration guides and reference materials, for the calibration of particle size spectrometers, pollen monitoring instruments and the chemical characterisation of ambient aerosols. The project will validate its developments using field campaigns and will support this with the development of portable instruments and software for the measurement of ambient aerosol particle concentrations under variable environmental conditions. Finally, the project also responds to current challenges regarding aerosol instruments used by non-experts. The overall goal of this project is to focus on the traceable measurement and characterisation of aerosols in the environment. The AEROMET project has continued under the new name of 19ENV08 AEROMET II Advanced Aerosol Metrology for Atmospheric Science and Air Quality and received funding until August 2023. This project 19ENV08 has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.