Measurement report: Investigation of pH- and particle-size-dependent chemical and optical properties of water-soluble organic carbon: implications for its sources and aging processes
<p>Knowledge of the chemical structures and optical properties of water-soluble organic carbon (WSOC) is critical considering its involvement in many key aerosol-associated chemical reactions and its potential impacts on climate radiative forcing. This study investigates the coupled effects of...
| Main Authors: | , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/13845/2022/acp-22-13845-2022.pdf |
| Summary: | <p>Knowledge of the chemical structures and optical properties of
water-soluble organic carbon (WSOC) is critical considering its involvement
in many key aerosol-associated chemical reactions and its potential impacts
on climate radiative forcing. This study investigates the coupled effects of
pH and particle size on the chemical structures (functional groups) and
optical properties (UV/fluorescence properties) of WSOC and further
explores the source and aging of WSOC constituents. The results showed that
the specific UV absorbance at a wavelength of 254 nm (SUVA<span class="inline-formula"><sub>254</sub></span>) and mass
absorption efficiency at a wavelength of 365 nm (MAE<span class="inline-formula"><sub>365</sub></span>) were higher in
smaller than larger particles, revealing the relatively higher
aromaticity/molecular weight and more freshness of WSOC in smaller
particles. A decrease in aromaticity/molecular weight of WSOC in larger
particles was caused by the degradation reaction that occurred during the
aging process. The carboxylic groups tend to be enriched in larger
particles, whereas the contribution of phenolic groups was generally higher
in smaller particles. The changes in the fluorescence peak position
suggested that hydroxyl groups play a leading role in pH-responsive
fluorescence in summer, while carboxylic and nitro groups play a dominant
role in winter. Overall, the chromophores in smaller particles showed a more
pronounced pH dependence, which might be related to the higher content of
aromatic species in WSOC in these particle size ranges. Specifically, the
climate impact of WSOC would be enhanced with increasing pH. The pH- and
particle-size-dependent chemical and optical properties of WSOC provide
insights into the structure, source, and aging of WSOC, which will
ultimately improve the accuracy of assessing the climate effects of WSOC.</p> |
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| ISSN: | 1680-7316 1680-7324 |