Emissions from residential wood combustion - Uncertainties run amuck

1. Emissions from residential wood combustion- Uncertainties run amuck Ole-Kenneth Nielsen, Malene Nielsen & Marlene Plejdrup Department of Policy Analysis National Environmental Research Institute Aarhus University 12th Joint EIONET and TFEIP Meeting Stockholm, May 2, 2011

2. Outline • Introduction • Significance of residential wood combustion • Uncertainties • Activity data • Emission factors • Different technologies • Different operating conditions • Different measurement methods • Conclusions

3. Introduction • Increased importance as legislative demands have reduced emissions from energy industries and manufacturing industries • Large public and media attention due to local nuisances caused by residential wood combustion – neighbour complaints • Danish legislation from 2008 • Emission limit values for PM from space heaters • Emission limit values for CO, HC and PM for boilers

4. Significance in Denmark

5. Activity data • Highly uncertain due to the large amount of non-traded wood • Large recalculation in Denmark in 2006 • Previously the official statistic was based on recorded sales and an assumed correction factor • Now wood consumption is based on recorded sales combined with a survey every second year • The survey uses telephone interviews to establish the wood consumption • Total wood consumption in residential plants in Denmark in 2009: 33,384 TJ ≈ 2.1 mio. ton

6. Time-series for firewood consumption in residential plants • The survey carried out in 2006 increased the firewood consumption in 2004 by 40 %

7. Emission factors • Heavily influenced by: • Technology: boilers vs. stoves – old appliances vs. new appliances • Operating conditions: batch size – log size etc. • Fuel quality: water content – wood species – ”clean” wood • Measurement method • EMEP/EEA Guidebook provides EFs for fireplaces, stoves, boilers, advanced fireplaces, advanced stoves and pellet stoves • The following will focus on PM emissions

8. Technology • Large differences between boilers and stoves and for old and new technologies

9. Technology • High variability of emission factors. However, clear indications that newer technologies have substantially lower emission factors compared to older technologies • Need for more technology dependent emission factors in the Guidebook • Important to have a detailed description of the technology for which the emission factors are applicable, due to significant technological development in later years

10. Operating conditions • Large differences in emissions for different operating conditions Derived from Klippel & Nussbaumer (2007)

11. Operating conditions • A study showed that big batch size significantly increased the emissions • Regarding log size the same study found that small logs resulted in higher emissions than big logs • Very difficult to completely take all conditions into account when deriving emission factors • Focus should be on ”typical” operating conditions • Important when using laboratory measurements that emission factors are not based on ideal conditions

12. Fuel quality • The water content will influence emissions. Most studies have not isolated the effect of water content • Studies have shown that PM emissions also depend on wood species. One study showed that oak had an emission factor (5.1 g/kg) of almost halve that of pine (9.5 g/kg) • The use of treated (painted, impregnated) wood or other waste fractions can significantly increase emissions. This factor has not been isolated in studies for residential wood combustion • All these elements will be extremely difficult to take into account in a national inventory

13. Measurement methods • There are several different methods available for measuring PM emissions, e.g. • In-stack gravimetric methods (e.g. VDI2066 bl.2) • Out-stack gravimetric methods without dilution tunnel (e.g. SS028426) • Gravimetric methods with dilution tunnel (e.g. NS3058) • The main difference is whether the measurement is carried out in the hot flue gas or after the semi-volatile compounds have condensed • To ensure comparability between emission inventories there is a need to establish a common method for deriving emission factors

14. The impact of measurement methods • Emissions measured in a dilution tunnel are 2.5-10 times higher than the solid particle emissions measured in the hot flue gas • A Danish test showed 4.8 times higher PM emissions when measured in a dilution tunnel compared to in-stack Nussbaumer, T., Klippel, N. & Johansson, L., 2008

15. Comparison between countries • Denmark uses the EMEP/EEA EFs for e.g. old wood stoves. This EF is very high compared to some other countries • The large difference can be attributed to different measurement methods • Germany and Sweden uses in-stack or heated out-stack measurements • Denmark (and e.g. Norway) uses out-stack measurements in a dilution tunnel

16. Conclusions • Residential wood combustion is in many countries a key category for several pollutants • Large uncertainties associated with: • Wood consumption • Technology • Operating conditions • Measurement method • The vastly different emission factors depending on measurement methods will be a problem if/when PM is included in the emission ceilings for 2020

17. Conclusions • The reporting guidelines and/or the Guidebook should address the issue of measurement methods to ensure consistent reporting and comparability between countries • The Guidebook should be improved to cover more technologies including modern technologies with low emission factors

18. Thank you for your attention