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Solene Turquety talks with
ScienceWatch.com and answers a few questions about
this month's New Hot Paper in the field of
Geosciences. The author has also sent along images of
their work.
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Article Title: Inventory of boreal fire emissions
for North America in 2004: Importance of peat burning and
pyroconvective injection
Authors: Turquety,
S;Logan, JA;Jacob, DJ;Hudman, RC;Leung, FY;Heald,
CL;Yantosca, RM;Wu, SL;Emmons, LK;Edwards, DP;Sachse,
GW
Journal: J GEOPHYS RES-ATMOS
Volume: 112, Issue: D12
Page: art., Year: no.-D12S03 APR 3 2007
* Natl Ctr Atmospher Res, Div Atmospher Chem, POB 3000,
Boulder, CO 80307 USA.
(addresses have been truncated)
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Why do you think your paper is highly
cited?
This paper describes and evaluates a daily inventory of the pollution
emitted by extremely large fires that burned millions of hectares of boreal
forests in Alaska and Canada during the summer of 2004. It was highly cited
for two main reasons.
First of all, the inventory developed was used in several studies. The
pollution resulting from these fires emitted into the atmosphere was huge,
affecting air quality locally but also on larger scales. Direct impact was
predicted and observed as far as the Southern United States and Europe. The
scientists therefore needed to account for this great perturbation of
atmospheric chemistry in their analyses. Furthermore, using a daily
inventory proved essential as the fires varied in location and intensity
through the summer.
Our study also highlighted several sources of uncertainties in current
inventories that need to be better accounted for: the contribution from the
burning of the surface layer in peatlands (large reservoir of carbon), and
the potential importance of injection at high altitude of fire emissions
for the modeling of pollution transport events.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
Rather than a new discovery or methodology, the strength of this paper
resided in its integrated approach of the different stages of the work:
starting with the development of a state-of-the-art emission inventory,
then incorporating the inventory into a global chemistry and transport
model to simulate their impact on atmospheric chemistry, and finally
confronting the simulations with the available atmospheric observations.
The comparisons allowed the evaluation of our knowledge and pointed out the
uncertainties without indulgence. It also allowed the formulation of
several hypotheses explaining the disagreements.
Would you summarize the significance of your paper
in layman's terms?
Wildfires constitute an important contribution to the emissions of
pollutants into the atmosphere, resulting in a strong perturbation of
atmospheric chemistry, affecting both air quality and climate. It is
essential to evaluate this contribution correctly—and this for each
fire season.
Fires are indeed highly variable in location and timing with large
interannual variability, but also large variations occur during the fire
seasons reflecting meteorological conditions, agricultural practices, and
accidental fires.
The summer of 2004 was characterized by strong fires in Alaska and Western
Canada which burned more than five million hectares between June
1st and August 31st—a record breaking fire
season for Alaska. We have developed a daily inventory of the emissions
associated with these fires and evaluated it using the available
observations of atmospheric composition.
We have focused on the emissions of carbon monoxide (CO) since there are a
lot of valuable observations for this molecule, in particular from the
Measurements of Pollution in the Troposphere (MOPITT)/Terra space-borne
instrument which allow the monitoring of CO total amounts with good spatial
resolution and coverage (global coverage every three days). This intense
burning also occurred as a field campaign sampling intercontinental
transport of pollution from fires was underway over the Northeastern United
States—the International Consortium for Atmospheric Research on
Transport and Transformation (ICARTT) campaign—so that a lot of
aircraft in situ observations were available.
The inventory of the areas burned was first developed combining reported
daily total areas burned in the different states and provinces of the US
and Canada, with hotspots detected in space by the Moderate-resolution
Imaging Spectroradiometer (MODIS) instrument. The resulting emissions were
then derived depending on the type of ecosystems burning, their
corresponding fuel loads, and emission factors.
We evaluated the contribution from the burning of peat, usually not
specifically accounted for in current inventories. This important carbon
reservoir proved to be a critical parameter since we evaluated that a third
of our total emissions of 30 teragrams of CO is associated with peat
burning. We then incorporated our inventory in the global chemistry and
transport model GEOS-Chem (Goddard Earth Observing System) developed at
Harvard University to simulate the impact of these emissions on atmospheric
composition. This allowed us to evaluate our inventory against the
available atmospheric observations of CO. These comparisons highlighted
good general consistency as well as the importance of the additional
contribution from peat burning. But they also showed that significant
uncertainties remain.
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"We have focused on
the emissions of carbon
monoxide (CO) since there are
a lot of valuable
observations for this
molecule"
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In particular, while the agreement is good above the source region (with a
small tendency to overestimate CO) we tend to underestimate CO downwind, in
the transported plume. This is still not well understood. An element of
explanation could be the injection at high altitude of emissions associated
with the largest fires. Indeed, some fires may have enough energy to inject
trace gases and particles as high as 10km into the free troposphere and
even into the stratosphere (so-called pyroconvective events). A simple
parameterization of injection height in our model shows the sensitivity of
the simulation for specific transport events which needs to be further
analyzed.
How did you become involved in this research, and
were there any problems along the way?
I came to work on the impact of boreal fires as part of my postdoctoral
research project at Harvard University—but quite by chance. I was
interested in the information on the intercontinental transport of
pollution provided by several new satellite missions. I became involved in
the ICARTT campaign, analyzing simulations of the atmospheric composition
and the transport of pollution.
Although we expected the boreal fires to have some impact during the
summer, it turned out that they were a major perturbation during the summer
of 2004. It was then urgent to include this parameter in the analyses of
the observations, and I chose to confront our knowledge of the expected
emissions with the wealth of available observations. Of course global model
simulations and observations were not in good agreement, revealing a large
underestimate of the fire emissions. The challenge was then to reconcile
emissions and observations, a huge work we hope we have contributed to in
this publication.
Where do you see your research leading in the
future?
Wildfire emissions are still subject to strong uncertainties. In order to
improve our knowledge of the emissions and their impact, it is essential to
have more observations close to fires with the use of experimental fires
and dedicated field campaigns.
The summer component of the POLARCAT international campaign conducted in the
summer of 2008 was largely dedicated to the sampling of boreal biomass
burning plumes, close to their emission regions and further downwind
after long range transport. The in situ data collected will
very certainly add a lot of input to our understanding of the emissions,
their export to the free troposphere and the chemical evolution of the
plumes. The overall objective of POLARCAT, which proposes a coordinated
program of measurements and modelling, is to quantify the impact of
trace gases, aerosols and mercury transported to the Arctic and their
contribution to pollutant deposition and climate change in the region.
New satellite observations of atmospheric chemistry, with improved
horizontal resolution and coverage, such as observations from the Infrared
Atmospheric Sounding Interferometer (IASI/METOP)
instrument, will also provide decisive long-term monitoring. In
particular, inverse modeling techniques using the observations as a
constraint to the emissions with a model as an intermediate are
increasingly used in the scientific community. More than the constrained
inventories, I am interested in the information the constraint may
provide on the processes we are currently missing.
My research is also dedicated to the quantification of the impact of these
wildfires in the Northern Hemisphere, both on air quality in the short
term, and on the global radiative forcing and thus on climate on a longer
term.
Do you foresee any social or political implications
for your research?
A significant increase of wildfires is predicted as a response to climate
change, particularly in the boreal regions. This additional forcing, and
the potential burning of large reservoirs of carbon such as peatlands, is
currently not included in the models. A better knowledge and understanding
of the evolution of wildfires and the associated emissions could therefore
be crucial both for air quality monitoring and forecasting during the fire
seasons, and for future projections.
Solène Turquety
Universite Pierre et Marie Curie
Laboratoire de Meteorologie Dynamique (LMD)
Ecole Polytechnique
Paris, France
Web
Keywords: boreal fire emissions, boreal forests in alaska and
canada, summer of 2004, pollution resulting from these fires, southern
united states and europe, burning of the surface layer in peatlands,
modeling of pollution transport events, strong perturbation of
atmospheric chemistry, affecting both air quality and climate,
meteorological conditions, agricultural practices, accidental fires,
emissions of carbon monoxide, measurements of pollution in the
troposphere, international consortium for atmospheric research on
transport and transformation, moderate-resolution imaging
spectroradiometer, goddard earth observing system, infrared atmospheric
sounding interferometer.
