A great deal of wood grows in Switzerland’s forests – more than is currently used: the forests are underutilised. Part of this wood could be used for the expansion of wood energy, for example for the heating of residential buildings. This would allow for the country’s dependency on fossil energy sources such as crude oil to be reduced. And because wood is CO2-neutral, this would also have a positive impact on the climate. Depending on the type of combustion applied, however, pollutants that are detrimental to health escape into the air. If wood heating systems are to be incorporated in settlements more often, it is important that suitable combustion types are selected and that these are operated in an optimal manner. Researchers from the Lucerne University of Applied Sciences and Arts and the Paul Scherrer Institute systematically tested various combustion systems as part of two sub-projects and analysed the resulting waste gases. A unique feature of the investigation was the fact that pollutants that only emerge following conversion upon meeting sunlight in the surrounding area were taken into account. These include secondary organic aerosols and reactive oxygen compounds that are harmful to health.