We report the emissions of glyoxal and methylglyoxal from the open burning of
biomass during the NOAA-led 2016 FIREX intensive at the Fire Sciences
Laboratory in Missoula, MT. Both compounds were measured using cavity-enhanced spectroscopy, which is both more sensitive and more selective than
methods previously used to determine emissions of these two compounds. A
total of 75 burns were conducted, using 33 different fuels in 8 different
categories, providing a far more comprehensive dataset for emissions than was
previously available. Measurements of methylglyoxal using our instrument
suffer from spectral interferences from several other species, and the values
reported here are likely underestimates, possibly by as much as 70 %.
Methylglyoxal emissions were 2–3 times higher than glyoxal emissions on a
molar basis, in contrast to previous studies that report methylglyoxal
emissions lower than glyoxal emissions. Methylglyoxal emission ratios for all
fuels averaged
In addition to the large primary emissions of gases and particulate matter,
the secondary chemistry that occurs downwind of fires can play an important
role in numerous atmospheric processes. Ozone (
Along with glyoxal and methylglyoxal, numerous other carbonyl species such as
formaldehyde have been detected in fire plumes
The column abundances of glyoxal and formaldehyde are enhanced in regions
influenced by biomass burning
Together, direct emissions from biomass burning and biofuel (biomass used as
an energy source) have been estimated to contribute 20 % of the glyoxal
budget but only 3.5 % of the methylglyoxal budget
Models have generally been able to reproduce the formaldehyde columns
observed by satellites
Setup of ACES, the OP-FTIR, and the PTR-ToF at the FSL during the
2016 campaign (diagram not to scale).
In this work we use cavity-enhanced spectroscopy (CES) to measure primary emissions of glyoxal and methylglyoxal from open burns conducted in a laboratory setting. These experiments were conducted as part of the NOAA-led Fire Influence on Regional and Global Environments Experiment (FIREX), which took place from October to November 2016 at the US Forest Service Fire Sciences Laboratory (FSL) in Missoula, MT. CES measurements of glyoxal and methylglyoxal are faster, more sensitive, and more specific than the methods used in previous studies. Over 30 different fuel types were burned during the 2016 FIREX campaign, and, combined with the other instrumentation deployed at the FSL, our data provide the most detailed look to date at direct emissions of glyoxal and methylglyoxal from biomass burning.
Burns were conducted at the FSL during the 2016 FIREX intensive
(
A total of 33 different fuels were used, including numerous burns of
coniferous fuels and chaparral species. For the conifers, burns were
conducted either using only one component (e.g., litter, canopy) or with
realistic mixes of several components. A full list of fuels in given in the
Table S1 in the Supplement and in
Details of the measurements and instruments used in this work. All three instruments can measure additional species not used in this analysis.
All the instruments used here have been described previously, so only brief
descriptions will be provided. The species-specific uncertainties for each
instrument are given in Table
Glyoxal and methylglyoxal were measured using the ACES instrument
ACES has a second channel centered at 375 nm measuring nitrous acid (HONO)
and
ACES was installed on the platform (see Fig.
The OP-FTIR measured carbon monoxide (
The PTR-ToF was used to measure VOCs with a proton affinity greater than that
of water, including formaldehyde, 2,3-butanedione, 2,3-pentanedione, and
several other carbonyl species, with a time resolution of 1 Hz
Fire-integrated emission ratios relative to
The glyoxal to formaldehyde ratio (
Data from a filter transmission experiment conducted in Boulder,
Colorado,
prior to the FIREX campaign. Shown are the retrieved glyoxal (green) and
The modified combustion efficiency, MCE, was calculated using
Previous work has shown that glyoxal loss to filters and any aerosol
particles collected on the filters is low
Prior to the deployment to the FSL, filter transmission tests were conducted
in Boulder, Colorado, by burning dried pine needles and branches in a small wood-burning stove and then adding glyoxal to the inlet using the bubbler. The
data from one of these tests are shown in Fig.
Unfortunately, during the FIREX campaign, the bubbler output frequently was
unstable, even over short (20 min) timescales. During times when the bubbler
was reasonably stable, the maximum observed loss was only 10 %, but the
instabilities in the bubbler output made it difficult to fully constrain this
number. Since we did not observe losses during the tests prior to FIREX and
given the uncertainty in the transmission measurements made during FIREX, we
have not corrected our data for filter loss, and note that our glyoxal
emissions might be up to 10 % low. Methylglyoxal is even less reactive than
glyoxal with respect to aerosol uptake
Glyoxal emission ratios and factors for all 75 burns are shown graphically in
Fig.
Glyoxal emission ratios for realistic mix burns averaged
These discrepancies in emission factors between the two laboratory studies
and the burns conducted at the FSL could be due to systematic differences in
the MCE between the two studies
Glyoxal emission factors
Examining emissions from individual fuels, peat had the lowest emission ratio
by a factor of 5, while rice straw and bear grass had the highest, consistent
with past results for emissions of larger oxygenated aliphatic compounds
We examined the relationship between EF and either MCE or fuel moisture
content to see if this could explain the variability in the observed EFs.
Emission factors as a function of MCE and moisture content are shown in
Fig.
Within certain fuel groups, some of the variability in the emission factors did appear to be driven by differences in the moisture content and MCE. The canopy burns of Engelmann spruce and subalpine fir with the highest emission factors also had moisture contents higher and MCE values lower than the other burns of that material. For most of the other fuel groups, the moisture content within the group did not vary significantly, making it difficult to fully constrain the relationship between glyoxal emissions and moisture content. Additionally, for some of the burns, there was significant variability in the emission factors despite similar conditions. For example, the two ponderosa pine litter burns were both dry (moisture contents of 0.11 and 0.07) and had similar MCEs, but the emission factors differed by a factor of 3. While moisture content and MCE can affect emissions, clearly there are other factors that also play a role.
Multiple burns of chaparral and coniferous fuels were conducted in 2016,
allowing for some investigation of the variability in emissions for those
fuels. However, there were several important fuels that were only burned
once, such as peat and rice straw. During El Niño years, peat fires can
emit almost as much non-methane organic carbon as all other biomass burning
combined and can negatively impact local-regional air quality
Glyoxal to formaldehyde ratios,
These values are at least an order of magnitude lower than those reported
from previous laboratory burns
Unlike the glyoxal emission ratios and factors,
Unlike the emission ratios and factors,
In addition to fire-averaged
Figure
In addition to formaldehyde, we compared emissions of glyoxal to several
other carbonyl species measured by the PTR-ToF: acetaldehyde, acetone,
2,3-butanedione, hydroxyacetone, and glycolaldehyde. The latter two of these
species are also measured by the OP-FTIR, but the PTR-ToF data were at the
same time resolution as the ACES data, so we chose to use those data here.
There is good overall agreement between the PTR-ToF and the OP-FTIR for these
species
Correlation plots for glyoxal relative to four other carbonyls for
Fire 027 (chamise chaparral). Shown are the plots for glyoxal versus
formaldehyde
Formaldehyde had the best correlation, with an average
While the
Figure
Fit results from the peak of emissions from Fire 060 (rice straw).
Other techniques for the measurement of methylglyoxal also suffer from
interferences. Methylglyoxal measurements by PTR-ToF are complicated by the
presence of an isomer, propenoic (acrylic) acid, which has been measured in
fire emissions at the FSL in 2009 using negative-ion proton-transfer
chemical-ionization mass spectrometry
Emissions at the FSL have also been analyzed using two-dimensional gas-chromatography time-of-flight mass spectrometry
ACES data from the FSL were analyzed in several ways to try to account for
the optical interference on the retrieved methylglyoxal concentrations. While
2,3-butanedione emissions are comparable to methylglyoxal emissions,
emissions of larger
In previous work, a third- or fourth-order polynomial was included in the fit
to account for drift in the instrument zero signal counts
When running the DOASIS fits without accounting for the other substituted
PTR-ToF data were only available for 58 burns, so all further discussion of the methylglyoxal emissions will be limited to results from those fires. All 33 fuel groups are still represented in this subset of fires.
The DOASIS software in principle can simultaneously retrieve the absolute
amounts of methylglyoxal and 2,3-butanedione, but this is complicated by the
similarities in the two cross sections and their lack of structure,
particularly at the low resolution (
Methylglyoxal emission ratios
Using the 2,3-butanedione concentrations measured by the PTR-ToF to correct
the methylglyoxal data could be complicated by the presence of other species
at the same mass. However, during FIREX, the contribution of different
species to the signal at the 2,3-butanedione mass of
Using 2,3-butanedione from the PTR-ToF to correct the ACES methylglyoxal did
not result in undesirable and unphysical behavior and reduced the
methylglyoxal emission ratios by
Shown in Fig.
Emissions of methylglyoxal from fresh ponderosa pine needles and dead
loblolly pine needles have been previously reported by
For all the burns, molar emissions of methylglyoxal exceeded those of
glyoxal, generally by a factor of 2 and by a factor of 15 for the duff burns.
This is consistent with the limited field data, which also found
methylglyoxal emissions to be higher than glyoxal emissions
Budgets for glyoxal and methylglyoxal predict that the largest global source
for both compounds is VOC oxidation
The effects of our revised emission factors on the global budgets for these
two compounds are harder to quantify.
The global glyoxal and methylglyoxal budgets by
Since
Emissions of glyoxal and methylglyoxal from biomass burning have been
determined for a number of different fuels, including peat, rice straw,
chaparrals, and numerous conifers. Both compounds were measured using cavity-enhanced spectroscopy, which for glyoxal provides a highly sensitive
measurement with minimal interferences. The detection of methylglyoxal using
this method suffers from interferences from structurally similar compounds,
but due to the high concentrations present, methylglyoxal emissions could be
constrained to within a factor of 2. Methylglyoxal emissions were higher
than glyoxal emissions, and some fuels that emitted little glyoxal emitted
large amounts of methylglyoxal. Primary emissions of glyoxal were
significantly lower than those reported in previous laboratory work, but they were
consistent with field measurements in fresh plumes. Glyoxal emissions showed
variability between fuel groups but in nearly all cases were well correlated
with emissions of formaldehyde. The ratio of glyoxal to formaldehyde was
consistent at 0.06–0.07 for many of the fuels, with the notable exceptions of
duff and peat, which had
Data from all instruments are publicly
available at
The supplement related to this article is available online at:
KJZ, SSB, RJY, and JMR designed the research. KJZ, VS, ARK, KS, MMC, BY, WPD, CW, JAdG, and SSB performed the measurements, contributed to the data analysis, or both. All authors participated in the discussion of the results and the writing of the paper.
The authors declare that they have no conflict of interest.
The authors thank Ryan Thalman (Snow College, UT) and Theodore Koenig (University of Colorado Boulder) for useful discussion. The authors also thank all those who helped organize and participated in the 2016 FIREX intensive, particularly Edward O'Donnell and Maegan Dills for lighting the fires, Ted Christian, Roger Ottmar, David Weise, Mark Cochrane, Kevin Ryan, and Robert Keane for assistance with the fuels, and Shawn Urbanski and Thomas Dzomba for logistical support. Support for Vanessa Selimovic and Robert J. Yokelson was provided by NOAA-CPO grant NA16OAR4310100. Abigail R. Koss was supported by funding from the NSF Graduate Fellowship Program. Kanako Sekimoto acknowledges funding from the Postdoctoral Fellowships for Research Abroad from Japan Society for the Promotion of Science (JSPS) and a Grant-in-Aid for Young Scientists (B) (15K16117) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. Matthew Coggon was supported by a CIRES Visiting Postdoctoral Fellowship. This work was also supported by NOAA's Climate Research and Health of the Atmosphere initiative. Edited by: Frank Keutsch Reviewed by: two anonymous referees