High time-resolved measurement of stable carbon isotope composition in water-soluble organic aerosols: method optimization and a case study during winter haze in eastern China
<p>Water-soluble organic carbon (WSOC) is a significant fraction of organic carbon (OC) in atmospheric aerosols. WSOC is of great interest due to its significant effects on atmospheric chemistry, the Earth's climate and human health. The stable carbon isotope (<span class="inline-...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-09-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/11071/2019/acp-19-11071-2019.pdf |
| Summary: | <p>Water-soluble organic carbon (WSOC) is a significant fraction of
organic carbon (OC) in atmospheric aerosols. WSOC is of great interest due
to its significant effects on atmospheric chemistry, the Earth's climate and
human health. The stable carbon isotope (<span class="inline-formula"><i>δ</i><sup>13</sup>C</span>) can be used to track
the potential sources and investigate atmospheric processes of organic
aerosols. However, the previous methods measuring the <span class="inline-formula"><i>δ</i><sup>13</sup>C</span>
values of WSOC in ambient aerosols require a large amount of carbon content, are time-consuming and require labor-intensive preprocessing. In this study,
a method of simultaneously measuring the mass concentration and the <span class="inline-formula"><i>δ</i><sup>13</sup>C</span> values of WSOC from aerosol samples is established by coupling the
GasBench II preparation device with isotopic ratio mass spectrometry. The
precision and accuracy of isotope determination is better than 0.17 ‰ and 0.5 ‰, respectively, for
samples containing WSOC amounts larger than 5 <span class="inline-formula">µg</span>. This method is then applied
for the aerosol samples collected every 3 h during a severe wintertime
haze period in Nanjing, eastern China. The WSOC values vary between 3 and 32 <span class="inline-formula">µg</span> m<span class="inline-formula"><sup>−3</sup></span>, whereas <span class="inline-formula"><i>δ</i><sup>13</sup>C<sub>−WSOC</sub></span> ranges from <span class="inline-formula">−26.24</span> ‰ to <span class="inline-formula">−23.35</span> ‰. Three different
episodes (Episode 1, Episode 2 and Episode 3) are
identified in the sampling period, showing a different tendency of <span class="inline-formula"><i>δ</i><sup>13</sup>C<sub>−WSOC</sub></span> with the accumulation process of WSOC aerosols. The
increases in both the WSOC mass concentrations and the <span class="inline-formula"><i>δ</i><sup>13</sup>C<sub>−WSOC</sub></span> values in Episode 1 indicate that WSOC is subject to
a substantial photochemical aging during the air mass transport. In Episode 2, the decline of the <span class="inline-formula"><i>δ</i><sup>13</sup>C<sub>−WSOC</sub></span> is accompanied
by the increase in the WSOC mass concentrations, which is associated with
regional-transported biomass burning emissions. In Episode 3, heavier
isotope (<span class="inline-formula"><sup>13</sup>C</span>) is exclusively enriched in total carbon (TC) in comparison to WSOC aerosols. This suggests that the non-WSOC fraction in total carbon may
contain <span class="inline-formula"><sup>13</sup>C</span>-enriched components such as dust carbonate, which is
supported by the enhanced <span class="inline-formula">Ca<sup>2+</sup></span> concentrations and air mass
trajectory analysis. The present study provides a novel method to
determine the stable carbon isotope composition of WSOC, and it offers
a great potential to better understand the source emission, the atmospheric
aging and the secondary production of water-soluble organic aerosols.</p> |
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| ISSN: | 1680-7316 1680-7324 |