ACTRIS-DK is the part of the pan-European Research Infrastructure ACTRIS-ERIC providing data and information about short-lived atmospheric constituents in natural and controlled atmospheres: ACTRIS . Research over the last decades has revealed strong interaction between air pollution and climate change. In particular, there has been a greater realisation that some air pollutants also act as short-term drivers of global warming. Detecting changes and trends in atmospheric composition and understanding their impact on the stratosphere and upper troposphere is necessary to establish the scientific links and feedbacks between climate change and atmospheric composition. The primary goal of ACTRIS-DK is to establish a top-level infrastructure in Denmark for studies of aerosols, reactive gases and clouds. The proposed combination and close linking of observational and exploratory platforms will provide outstanding research opportunities and provide the Danish society with a science based platform for decisions related to air quality and climate. The primary objective of ACTRIS is to provide the 4D-variability (space and time) of clouds and of the physical, optical and chemical properties of short-lived atmospheric species (reactive gases and aerosols), from the surface throughout the troposphere to the stratosphere, with the required level of precision, coherence and integration needed to determine their impact on climate and health.The second objective is to provide effective access to this information and the means to more efficiently use the complex and multi-scale ACTRIS parameters serving a vast community of users working on models, satellite retrievals, and analysis and forecast systems.The third objective is to raise the level of technology used in the research infrastructure (RI) and the quality of services offered to the community of users, involving partners from the private sector.Finally, the fourth objective of ACTRIS is to promote training of researchers, innovators and students, and strengthen the links between research, education and innovation in the field of atmospheric science. Our user group includes two cleantech University spin-off companies, Infuser and Airlabs, working in the area of pollution control and pollution sensors.