As a renewable and local raw material, wood has the potential to reduce our dependence on energy imports. Wood is CO2-neutral, and therefore a climate-friendly source of energy. However, burning wood generates not only heat but also many air pollutants, including carbon monoxide, methane, nitrogen oxides, volatile organic compounds and particulate matter, which are produced directly during combustion. Later, when the exhaust gases are exposed to sunlight, additional particulate matter and other pollutants can also be produced, for example so-called reactive oxygen compounds. Up until now, these have rarely been considered in investigations of combustion processes and flue gases. For this reason, researchers at the Paul Scherrer Institute have used special measuring instruments to measure both the directly emitted and the secondarily generated pollutants.