This inter-journal special issue of AMT, ACP, and GMD serves as a thematic collection for manuscripts arising from the work of Horizon 2020 integrated infrastructure project Eurochamp-2020; cf. https://www.eurochamp.org/ . As Eurochamp-2020 has project parts dealing with new instrumentation, with atmospheric chemistry and physics studies as well as with modelling, contributions are expected for all three journals as part of the inter-journal special issue.

The Sentinel-5 Precursor mission is a single-payload satellite in a low-Earth orbit successfully launched on 13 October 2017. The mission provides daily global information at an unprecedented spatial resolution (~3.5x7km²) on trace gases and aerosols, important for air quality, climate forcing, and the ozone layer. The single payload of the mission is the TROPOspheric Monitoring Instrument (TROPOMI), which is a nadir-viewing push-broom spectrometer measuring in the ultraviolet, visible, near infrared, and shortwave infrared. The selected wavelength range allows for the observation of key atmospheric constituents, including O₃, NO₂, CO, SO₂, CH₄, CH₂O, aerosols, and clouds. The mission flies in loose formation with Suomi NPP to obtain detailed information on clouds and for further scientific exploitation of combined data products. In this combined ACP/AMT special issue the first results will be presented, including validation of operational products.

The purpose of this special issue is the compilation of modelling and observational studies in connection with five international field deployments (AEROCLO-sA, CLARIFY, LASIC, ORACLES, and NaFoLiCA) that focus on the interactions of natural and anthropogenic aerosols with radiation, clouds, and regional climate in the South Atlantic Ocean and the southern African region. These deployments, based in Namibia, Ascension Island, and São Tomé, took place between 2016 and 2018 and support a significant number of investigations extending beyond just the individual science teams. The airborne and ground-based observations, as well as the related satellite measurements and climate modelling studies, address all aspects of aerosol–cloud–climate interactions, including the link of aerosol properties to meteorological fields and dynamical processes that influence aerosol emission and transport. The projects also target the advancement of remote sensing of aerosols for complex scenes over land, sea, and clouds. The special issue will be open to all submissions, with complementary goals to the five mentioned deployments, so as to encourage the exchange of ideas from inside and outside the science teams of all projects.

We conducted the Fifth International Workshop on Ice Nucleation (FIN) to (1) understand the microphysics of how particles nucleate ice, (2) determine the number of ice forming particles as a function of atmospheric properties such as temperature and relative humidity, (3) measure the atmospheric distribution of ice forming particles and (4) ascertain the role of anthropogenic activities in producing or changing the behaviour of ice forming particles. To accomplish these goals we held three distinct workshops on the topic of atmospheric ice nucleation. The first was an intercomparison of instruments to determine the composition of ice forming particles in a controlled laboratory setting. This took place in autumn 2014 at the location of the last ice nucleation instrument intercomparison: the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) chamber located at the Karlsruhe Institute of Technology. The second was an intercomparison of instruments used to determine cloud formation conditions. This activity also took place at AIDA and was conducted in spring 2015. Because ice nucleation predominantly takes place at the low temperatures found at high altitude, a critical requirement for the third workshop was a facility that offers access to free-tropospheric air masses with minimal local particle sources. We used the Desert Research Institute’s recently renovated Storm Peak Laboratory for this workshop in autumn 2015.

This special issue aims to highlight advances in spectroscopic techniques for applications in atmospheric science. It will highlight cutting-edge measurements of atmospherically relevant species, including aerosol, isotopologues, and trace gases, using optical cavity-based techniques. Such techniques can include cavity-enhanced methods for sensitive absorption and extinction measurements as well as advances in frequency comb techniques. Techniques based on both broadband and laser sources from the ultraviolet to infrared will be considered. Papers based on both laboratory and field measurements are welcome.