Composition and light absorption of N-containing aromatic compounds in organic aerosols from laboratory biomass burning
<p>This study seeks to understand the compositional details of N-containing aromatic compounds (NACs) emitted during biomass burning (BB) and their contribution to light-absorbing organic carbon (OC), also termed brown carbon (BrC). Three laboratory BB experiments were conducted with two Unite...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/2899/2019/acp-19-2899-2019.pdf |
| Summary: | <p>This study seeks to understand the compositional details of N-containing
aromatic compounds (NACs) emitted during biomass burning (BB) and their
contribution to light-absorbing organic carbon (OC), also termed brown carbon
(BrC). Three laboratory BB experiments were conducted with two United States pine
forest understory fuels typical of those consumed during prescribed fires.
During the experiments, submicron aerosol particles were collected on filter
media and subsequently extracted with methanol and examined for their optical
and chemical properties. Significant correlations (<span class="inline-formula"><i>p</i><0.05</span>) were
observed between BrC absorption and elemental carbon <span class="inline-formula">(EC)∕OC</span> ratios for
individual burns data. However, the pooled experimental data indicated that
<span class="inline-formula">EC∕OC</span> alone cannot explain the BB BrC absorption. Fourteen NAC formulas were
identified in the BB samples, most of which were also observed in simulated
secondary organic aerosol (SOA) from photooxidation of aromatic volatile organic compounds (VOCs) with
<span class="inline-formula">NO<sub><i>x</i></sub></span>. However, the molecular structures associated with the identical NAC
formula from BB and SOA are different. In this work, the identified NACs from
BB are featured by methoxy and cyanate groups and are predominately
generated during the flaming phase. The mass concentrations of identified
NACs were quantified using authentic and surrogate standards, and their
contributions to bulk light absorption of solvent-extractable OC were also
calculated. The contributions of identified NACs to organic matter (OM) and
BrC absorption were significantly higher in flaming-phase samples than those
in smoldering-phase samples, and they correlated with the <span class="inline-formula">EC∕OC</span> ratio
(<span class="inline-formula"><i>p</i><0.05</span>) for both individual burns and pooled experimental data, indicating that
the formation of NACs from BB largely depends on burn conditions. The average
contributions of identified NACs to overall BrC absorption at 365 <span class="inline-formula">nm</span> ranged
from <span class="inline-formula">0.087±0.024</span> % to <span class="inline-formula">1.22±0.54</span> %, which is 3–10 times higher than
their mass contributions to OM (<span class="inline-formula">0.023±0.0089</span> % to <span class="inline-formula">0.18±0.067</span> %), so the NACs with light absorption identified in this work from BB
are likely strong BrC chromophores. Further studies are warranted to identify
more light-absorbing compounds to explain the unknown fraction (<span class="inline-formula">>98</span> %) of BB BrC absorption.</p> |
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| ISSN: | 1680-7316 1680-7324 |