1 Background 4 Objectives and coverage 4

3.2 Impact on air quality

To overcome this, a non-exhaustive literature review was carried out aiming to quantitatively assess the contribution from residential combustion to concentrations of ambient pollutants, using receptor, tracer and dispersion modelling tools (ETC/ACM, 2016a). Results evidenced that residential combustion of wood has an impact on local and regional-scale air quality (quantified for PM₁₀, PM_2.5, organic carbon (OC), elemental carbon (EC), and black carbon (BC)). Contributions from residential wood combustion to PM₁₀ and PM_2.5 concentrations during the winter range from <5% to up to 40% of daily means. The highest winter contributions are reported in the Alpine Valleys, the Po Valley, Oslo, Zurich, and rural areas in Austria and Germany. As expected, the lowest contributions are reported for Southern European regions (e.g., Barcelona). Several studies carried out in urban areas (e.g., Vienna, Berlin, Zurich) report that the PM₁₀ or PM_2.5 from residential combustion originates mainly from regional-scale transport, and that only a minor proportion is emitted locally.

The data available for OC, EC, or BC are scarcer than for PM, but still representative for their respective study areas. In regions such as Lombardy (Italy) or Zurich (Switzerland), wood combustion contributed with around 25-35% to ambient EC mass concentration. Furthermore, wood combustion contributes up to 50% of OC mass concentration during the winter heating period and especially in central Europe (Austria, Po Valley) (ETC/ACM, 2016a, and references therein).

3.3 Mitigating emissions from residential wood combustion

1. 
   the use of non-regulated stoves,
   
2. 
   the inadequate maintenance of old or new stoves installed in homes, and/or
   
3. 
   the use of non-standardised fuels (including treated, painted or not sufficiently dried wood, or even agricultural waste) generate persistent organic pollutant (POP) and metal emissions, as well as hinder an efficient combustion (AIRUSE, 2015; Viana et al., 2013; Kubica et al., 2007).
   

Still, combustion of dry untreated biomass in new ovens and under appropriate operating conditions may lead to higher emissions of PM and PAHs than residential combustion of gas or oil, which are fossil fuels with higher CO₂ emissions (Tønnesen and Høiskar, 2013). A possible way of avoiding a massive substitution of gas and oil burners with biomass stoves in urban areas, and the associated negative impacts on air quality and health, would be the use of biomass in district heating. The use of electrostatic precipitators in biomass boilers may decrease particle emissions to the same level or even lower as in heavy fuel-oil combustion, even if fuel-oil emits larger particle number concentrations of smaller particles (Sippula et al., 2009). Other possible mitigation measures are presented in box 3.2.

The Ecodesign Directive (EU, 2009b) provides EU-wide rules for improving the environmental performance of energy related products through eco-design. It refers to energy-using products, that is, products which use, generate, transfer or measure energy (e.g., boilers), as well as to other energy related products which do not use energy but have an impact on energy. Its aim is to transition towards better (more efficient, lower emissions) stoves and boilers over the next decade.

The Directive on the on the energy performance of buildings (EU, 2010b), though not targeting specifically wood burning, promotes the improvement of the energy performance of buildings within the Union, in order to reduce energy consumption for heating.

At national level

National regulations for small combustion installations vary widely in terms of which and how strictly emissions are regulated or to which product types regulations apply. Almost all of them include only type testing requirements for new products to be put on the market, but no requirements for existing installations. So far, Germany is the only country in Europe with a regulation that controls explicitly the emissions of existing small combustion installations.

Some countries have set up labelling schemes in order to promote small biomass solid fuel combustion technology development through voluntary labelling, mostly with a focus on thermal efficiency. Existing labels include the “Umweltzeichen 37” (Austria) for wood/pellet-fired heaters, “Flamme Verte” (France), the “Blue Angel” (Germany) for pellet stoves and pellet boilers, “DINplus” marking for room heaters and inserts (Germany), the “sign for ecological safety” for boilers (Poland), and “P-marking” (Sweden). Transnational labelling schemes include the “Nordic Swan” for slow heat release, stove and insert appliances (Sweden, Denmark, Finland, Norway) or the label of the European Fireplace Association (EFA), which may be applied to solid fuel heaters all over Europe.

Local scale strategies focus mainly on providing guidance on the best usage and maintenance of stoves. Recommendations and incentives to promote the replacement of old stoves and the use of recommended fuels are provided by e.g., the UK DEFRA or the Madrid (Spain) regional government (www.cambiatucaldera.com), and several Norwegian municipalities (ETC/ACM, 2016a).

Bans or restrictions on solid fuel combustion in households in certain areas or periods of time (e.g., during strong air stagnation events) are also implemented (e.g. Malmø) or contemplated.