31 May 2010
By Jens C. Pedersen
The contribution to air pollution from residential
wood combustion has now been mapped in unprecedented
detail by researchers from
the National Environmental Research Institute
(NERI), Aarhus University. A comprehensive
monitoring campaign in the Danish town Slagslunde
indicates that residential wood combustion
is a major contributor to particle pollution.
When compared to the amount of heat produced,
pollution from wood stoves far exceeds that
from other methods of heating. However,
the results also indicate a possible overestimation
of the total emission from residential wood
combustion in Denmark.
NERI researchers specialising
in air pollution have focused on the Danish
village Slagslunde in North Sjælland.
Not because this is an area with a particularly
high level of air pollution, but because
the researchers needed an area with a high
proportion of wood burning stoves, where
users of wood burning stoves could also
provide detailed information about their
wood burning habits. The successful project
gave the NERI researchers an unprecedented
insight into the habits of users of wood
burning stoves and the resulting impact
on air pollution. Project leader Helge Rørdam
Olsen, NERI, describes the results:
”We have achieved a
unique insight into the wood burning habits
of the Danes. At the same time our measurements
have provided us with a "fingerprint"
of the pollution caused by residential wood
combustion. This is a useful tool when distinguishing
between contributions from wood smoke and
contributions from other sources.”
Helge Rørdam
Olesen draws attention to a fact, which
may cause confusion in the public debate
about pollution from residential wood combustion:
“When discussing particle
pollution it is important to make a distinction
between the emission of particles and the
concentration of particles in the outdoor
air. There is a difference, because only
a fraction of the particles in the outdoor
air were “born” as particles – these are
the so-called primary particles. A large
proportion of the outdoor particles were
not born as particles, but as gases. Consequently,
although residential wood combustion is
responsible for more than half of the total
Danish emission of primary particles, the
contribution to the particle concentration
in outdoor air is far below 50%. Other major
sources are shipping, agriculture, traffic,
and transboundary contributions.”
The investigation indicates
that in an area with a high degree of wood
combustion activity – such as Slagslunde
– the contribution from residential wood
combustion to the concentration of fine
particles (PM2.5) will amount to approx.
2 micrograms per m3 on a yearly basis in
a year with normal weather conditions. The
corresponding figure for another previously
monitored area, the village of Vindinge,
which has less wood burning activity is
ca. 0.5 micrograms per m3. These figures
can be compared to the level of PM2.5 concentration
in background air, which amounts to 10-15
micrograms per m3. Thus, for an area with
a high level of wood combustion activity
the contribution from residential wood combustion
constitutes 10-20% of the particle pollution.
This applies to the yearly average, while
during cold spells the contribution will
be considerably higher.
When the scientists
compare their measurements of pollution
in the air with results of model calculations
based on wood burning habits they are able
to perform backward calculations of the
so-called emission factors, i.e. the amount
of grams emitted particles per kilo burnt
wood. It is difficult to estimate emission
factors of general validity, because besides
depending on the wood stove, the emission
factor is very sensitive to the habits of
the “stove keeper”.
The results indicate
that the emission factors in Slagslunde
are somewhat lower than the factors usually
applied in Danish emission inventories.
Helge Olesen comments:
“It is difficult to draw definitive conclusions
as there are many uncertainties involved.
If, for example, the closest neighbours
to the monitoring station belong to the
group of very careful stove keepers – possibly
encouraged by the surrounding the monitoring
campaign – the results cannot be considered
generally representative for Denmark.”
NERI researchers have
previously demonstrated that the firing
habits of wood stove users are extremely
important to emissions. Emission levels
10-100 times above normal can occur as the
result of old stoves, wrong wood burning
habits or burning of wet wood and waste.
Part of large cooperation
The investigations are part of the research
project WOODUSE, an inter-disciplinary project
covering many aspects of wood burning. The
project comprises investigations of emissions,
pollution levels in indoor and outdoor air,
impacts on health, and social aspects. Four
institutions have taken part in the project
(NERI; the National Research Centre for
the Working Environment; Department of Public
Health, University of Copenhagen; Department
of Civil Engineering, Technical University
of Denmark). The project is funded by the
Danish Council for Strategic Research.
+ More
NERI hosts European
workshop on otters
26 May 2010
By Morten Elmeros
On 24-27 February 2010 the National Environmental
Research Institute (NERI) at Aarhus University
hosted a European workshop on post mortem
examination of otters.
The objective of the
workshop was to formulate common guidelines
for the information collection and examination
of dead otters and at the same time attend
to as many interests as possible to achieve
cross-boundary comparability as the collection
and examination methods of otters currently
vary among the European countries. The workshop
resulted in a proposal for common guidelines
for the autopsy of dead otters. The proposal
will be presented at the next international
otter conference under the auspices of the
International Union for Conservation of
Nature (IUCN).
Eighteen veterinaries
and biologists from nine European countries
participated in the workshop held at Kalø.
The workshop was arranged on behalf of IUCN’s
otter specialist group in a cooperation
between NERI and the Swedish Museum of Natural
History in Stockholm. The workshop was held
within the framework of the Danish Centre
for Wildlife Health.
The workshop included
several practical exercises. Here, the British
veterinary Vic Simpson performs the post
mortem examination. Simpson has examined
dead otters, collected systematically throughout
England for several decades . Photo: Hugh
Jansman.
