The influence of wood burning on air pollution is often underestimated. Diesel vehicles are indeed the most important source of harmful nitrogen oxides (NOx). However, it is still wrongly assumed that traffic is still by far the largest source of particulate matter and soot: Due to the use of filter technology, particulate emissions from the engines of passenger cars, trucks, etc. have been falling for years - they are now below the emissions from wood burning. Heating with wood must therefore increasingly be the focus of public and political debate.
Where do particulate matter and soot come from?
Small-scale combustion is already the largest source of particulate matter, soot (black carbon) and benzo(a)pyrene (BaP) in the EU (see EEA Air Quality Report). This is also reflected at regional level: According to the Environment Agency (LUBW) in Baden-Württemberg, for example, stoves and the like are responsible for around 38% of particulate matter (PM2.5) and more than 44% of BaP emissions in the southwestern part of Germany.
Projections by the renowned Austrian research institute IIASA (International Institute for Applied Systems Analysis) assume that domestic heating will account for more than 40% of particulate matter and almost 70% of soot emissions in Europe in 2030 (see chart on the right).
Which types of plants cause the most emissions?
A closer look at which wood combustion plants are particularly relevant reveals a clear picture: local space heaters or stoves fired with logs are responsible for the vast majority of emissions. According to a study by the German Biomass Research Centre, almost 80% of the dust from wood combustion can be attributed to these appliances. Wood burning stoves (free-standing local space heaters) play the largest role in this respect. In addition, tiled stoves, storage stoves and fireplace inserts also belong to the category of local space heaters. Boilers, i.e. central wood heating systems, are responsible for about one-fifth of the particles.
Can the indoor air also be affected by my own stove?
Indoor air can be polluted by various particle sources such as candles or toasters. However, many stove owners are not aware that heating with wood can also be a relevant source of pollutants within their own home. This danger exists in particular when opening of the furnace door fuel to refill fuel, as well as through leaking systems. In new, well-insulated houses there is another problem: here, the chimney draught sometimes "fights" against the in-house ventilation system or the extractor hood in the kitchen.
Measurements in the context of Clean Heat showed an increased indoor pollution with several stoves tested. For example, the indoor pollution while using a new Scandinavian eco-labelled stove (Nordic Swan) increased to over 160,000 particles per cubic centimeter (see diagram on the right). This corresponds to four times the load measured on the busiest road in Copenhagen.