Materials such as sulphates and organics, which mainly come from man-made sources, are emitted in the gas phase and some ultimately end up coating particles in the atmosphere. Some particles, in particular mineral dust, effectively form ice clouds, which, in turn, affect climate by interacting with solar and terrestrial radiation.
To understand the effect that coatings might have on the cloud-forming potential of atmospheric particles we used a large temperature and pressure-controlled "cloud chamber" located at the Karlsruhe Institute of Technology to mimic how atmospheric clouds form. Our results show that, while bare mineral dust particles are very efficient at forming clouds, a thin coating of sulphates or organics actually prevents the formation of ice until much lower temperatures or higher relative humidities are reached. This means that man-made pollutants might affect how clouds are formed in the atmosphere and how long they last.
These effects have not yet been extensively considered in modelling studies. More research is thus needed to determine the effects of other particles, coating thicknesses and types.
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