Spectral optical properties of soot: laboratory investigation of propane flame particles and their link to composition
<p><span id="page6408"/>Soot aerosol generated from the incomplete combustion of biomass and fossil fuels is a major light-absorber; however its spectral optical properties for varying black carbon (BC) and brown carbon (BrC) content remain uncertain. In this study, soot aeroso...
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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2025-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/6407/2025/acp-25-6407-2025.pdf |
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| Summary: | <p><span id="page6408"/>Soot aerosol generated from the incomplete combustion of biomass and fossil fuels is a major light-absorber; however its spectral optical properties for varying black carbon (BC) and brown carbon (BrC) content remain uncertain. In this study, soot aerosols with varying maturity and composition, i.e. elemental-to-total-carbon ratio (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">EC</mi><mo>/</mo><mi mathvariant="normal">TC</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="38pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="a434d3ed47844dbe9a7417ac781bab9e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-6407-2025-ie00001.svg" width="38pt" height="14pt" src="acp-25-6407-2025-ie00001.png"/></svg:svg></span></span>), have been studied systematically in a large simulation chamber to determine their mass absorption, scattering, and extinction cross sections (MAC, MSC, MEC); single-scattering albedo (SSA); and absorption and scattering Ångström exponents (AAE, SAE). The MAC, MEC, SSA, and AAE show a variability between the different types of soot with varying <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">EC</mi><mo>/</mo><mi mathvariant="normal">TC</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="38pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="d98c3dd06629c9ce353405ed57451d0d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-6407-2025-ie00002.svg" width="38pt" height="14pt" src="acp-25-6407-2025-ie00002.png"/></svg:svg></span></span> ratios. The MAC (MEC) at 550 nm increases for increasing <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">EC</mi><mo>/</mo><mi mathvariant="normal">TC</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="38pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="7c7ca3abf63eb567996671d1b7f250c0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-6407-2025-ie00003.svg" width="38pt" height="14pt" src="acp-25-6407-2025-ie00003.png"/></svg:svg></span></span>, with values of 1.0 (1.4) m<span class="inline-formula"><sup>2</sup></span> g<span class="inline-formula"><sup>−1</sup></span> for <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">EC</mi><mo>/</mo><mi mathvariant="normal">TC</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="38pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="54ffed50687805c6f186d5877b6bdd3b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-6407-2025-ie00004.svg" width="38pt" height="14pt" src="acp-25-6407-2025-ie00004.png"/></svg:svg></span></span> <span class="inline-formula">=</span> 0.0 (BrC-dominated soot) and 4.6 (5.1) m<span class="inline-formula"><sup>2</sup></span> g<span class="inline-formula"><sup>−1</sup></span> for <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">EC</mi><mo>/</mo><mi mathvariant="normal">TC</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="38pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="16b788defa5a132fb643f6a1bb090717"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-6407-2025-ie00005.svg" width="38pt" height="14pt" src="acp-25-6407-2025-ie00005.png"/></svg:svg></span></span> <span class="inline-formula">=</span> 0.79 (BC-dominated soot). The AAE and SSA (550 nm) decrease from 3.79 and 0.29 (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">EC</mi><mo>/</mo><mi mathvariant="normal">TC</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="38pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="0f8b86a481edcacac1ef37cd868a5b8b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-6407-2025-ie00006.svg" width="38pt" height="14pt" src="acp-25-6407-2025-ie00006.png"/></svg:svg></span></span> <span class="inline-formula">=</span> 0.0) to 1.27 and 0.10 (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">EC</mi><mo>/</mo><mi mathvariant="normal">TC</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="38pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="1c460d6c2eab28f7193cb4f3294a7110"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-6407-2025-ie00007.svg" width="38pt" height="14pt" src="acp-25-6407-2025-ie00007.png"/></svg:svg></span></span> <span class="inline-formula">=</span> 0.79). Combining present results for soot from propane combustion with literature data for flame soot from diverse fuels supports a generalised exponential relationship between particle <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">EC</mi><mo>/</mo><mi mathvariant="normal">TC</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="38pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="e5fb6256d98cd87c1d78541e399c7371"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-6407-2025-ie00008.svg" width="38pt" height="14pt" src="acp-25-6407-2025-ie00008.png"/></svg:svg></span></span> and its MAC and AAE values <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><msub><mi mathvariant="normal">MAC</mi><mn mathvariant="normal">550</mn></msub><mo>=</mo><mo>(</mo><mn mathvariant="normal">1.3</mn><mo>±</mo><mn mathvariant="normal">0.05</mn><mo>)</mo></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="111pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="cdb2fc036bea96fec148c35e0bf563a1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-6407-2025-ie00009.svg" width="111pt" height="13pt" src="acp-25-6407-2025-ie00009.png"/></svg:svg></span></span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M18" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi>e</mi><mrow><mo>(</mo><mn mathvariant="normal">1.8</mn><mo>±</mo><mn mathvariant="normal">0.1</mn><mo>)</mo><mfenced open="(" close=")"><mfrac><mi mathvariant="normal">EC</mi><mi mathvariant="normal">TC</mi></mfrac></mfenced></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="60pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="a6a8d7c905cd62cf94a92612e92feafb"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-6407-2025-ie00010.svg" width="60pt" height="15pt" src="acp-25-6407-2025-ie00010.png"/></svg:svg></span></span>; <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi mathvariant="normal">AAE</mi><mo>=</mo><mo>(</mo><mn mathvariant="normal">0.73</mn><mo>±</mo><mn mathvariant="normal">0.12</mn><mo>)</mo><mo>+</mo><mo>(</mo><mn mathvariant="normal">3.29</mn><mo>±</mo><mn mathvariant="normal">0.12</mn><mo>)</mo></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="170pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="d4034e21b8206d1c809b37bf1ce1fe19"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-6407-2025-ie00011.svg" width="170pt" height="12pt" src="acp-25-6407-2025-ie00011.png"/></svg:svg></span></span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M20" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi>e</mi><mrow><mo>-</mo><mo>(</mo><mn mathvariant="normal">2.32</mn><mo>±</mo><mn mathvariant="normal">0.30</mn><mo>)</mo><mfenced open="(" close=")"><mfrac><mi mathvariant="normal">EC</mi><mi mathvariant="normal">TC</mi></mfrac></mfenced></mrow></msup><mo>)</mo></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="78pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="4366cdc51fd2f29d7953dfc106a43db3"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-6407-2025-ie00012.svg" width="78pt" height="17pt" src="acp-25-6407-2025-ie00012.png"/></svg:svg></span></span>, which represents the optical continuum of spectral absorption for soot with varying maturity. From this, it is possible to extrapolate a MAC of 7.9 and 1.3 m<span class="inline-formula"><sup>2</sup></span> g<span class="inline-formula"><sup>−1</sup></span> (550 nm) and an AAE (375–870 nm) of 1.05 and 4.02 for pure EC (BC-like) and pure OC (BrC-like) soot. The established relationship can provide a useful parameterisation for models to estimate the absorption from combustion aerosols and their BC and BrC contributions.</p> |
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| ISSN: | 1680-7316 1680-7324 |