emissions from residential wood combustion - uncertainties run amuck

NATIONAL ENVIRONMENTAL RESEARCH INSTITUTE

AARHUS UNIVERSITY

Emissions from residential wood combustion - Uncertainties run amuck

Ole-Kenneth Nielsen, Malene Nielsen & Marlene PlejdrupDepartment of Policy AnalysisNational Environmental Research InstituteAarhus University

12th Joint EIONET and TFEIP MeetingStockholm, May 2, 2011


AARHUS UNIVERSITY May 2, 2011Ole-Kenneth Nielsen

Outline› Introduction

› Significance of residential wood combustion

› Uncertainties› Activity data› Emission factors

› Different technologies› Different operating conditions› Different measurement methods

› Conclusions



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



Significance in DenmarkShare of national

total in 2009

SO2 5.7 %

NOx 3.1 %

NMVOC 15.3 %

CH4 1.9 %

CO 27.0 %

N2O 0.7 %

NH3 0.2 %

TSP 45.3 %

PM10 55.1 %

PM2.5 67.9 %

HCB 24.7 %

PCDD/F 47.1 %

Share of national total in 2009

As 5.6 %

Cd 17.5 %

Cr 8.8 %

Cu 0.6 %

Hg 2.6 %

Ni 1.4 %

Pb 12.9 %

Se 0.1 %

Zn 9.2 %

Benzo(a)pyrene 85.3 %

Benzo(b)flouranthene 82.2 %

Benzo(k)flouranthene 85.3 %

Indeno(1,2,3-c,d)pyrene 81.3 %



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



Time-series for firewood consumption in residential plants

› The survey carried out in 2006 increased the firewood

consumption in 2004 by 40 %

0

5000

10000

15000

20000

25000

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

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Firewood consumption, 2005 statistics Firewood consumption, 2006 statistics



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



Technology› Large differences between boilers and stoves

and for old and new technologies

TechnologyEmission

factor Reference

Wood boiler (TSP, old boilers) 588-736Winther,

2008

Wood boiler (TSP, newer boilers) 96-335Winther,

2008

Wood boiler (TSP, modern boilers) 64-233Winther,

2008

Open fire place (PM10, conventional) 1188 Basrur, 2002

Open fire place (PM10, advanced) 313 Basrur, 2002

Wood stove (PM10, conventional) 875-1438 Basrur, 2002

Wood stove (PM10, advanced) 313 Basrur, 2002



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



Operating conditions› Large differences in emissions for different

operating conditions

Derived from Klippel & Nussbaumer (2007)

PM g/GJ Reference

Wood boiler (Old) 87-2200 Johansson et al., 2004

Wood stove (Old) 344-5075 Glasius et al., 2005

Wood boiler (Old) 963-1481 Glasius et al., 2005

Open fire place 170-780 Purvis & McCrills, 2000

Pellet boiler 16-27 Tissari, 2008

Pellet stove 11-81 Boman, 2005



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



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



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



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



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

g pr. GJ Denmark Sweden Germany Ireland Finland Austria

TSP EF for wood stoves 850 100 72 300 400 148

› 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



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



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


AARHUS UNIVERSITY

Thank you for your attention

emissions from residential wood combustion - uncertainties run amuck

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