Significant seasonal changes in optical properties of brown carbon in the midlatitude atmosphere
<p>Atmospheric brown carbon (BrC) plays significant roles in the light absorption and photochemistry of the atmosphere. Although the sources and occurrences of BrC have been studied extensively, its removal processes and optical characteristics in the atmosphere have been poorly understood. In...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/20/2709/2020/acp-20-2709-2020.pdf |
| Summary: | <p>Atmospheric brown carbon (BrC) plays significant roles in
the light absorption and photochemistry of the atmosphere. Although the
sources and occurrences of BrC have been studied extensively, its removal
processes and optical characteristics in the atmosphere have been poorly
understood. In this study, we examined the seasonal changes in sources and
sinks of BrC and water-soluble organic carbon (WSOC) in the atmosphere of
Seoul, South Korea. Our results showed that the concentrations of BrC and WSOC
decreased by approximately 80 % and 30 %, respectively, from the cold
season (October–January) to the warm season (June–September). Excitation–emission matrix
(EEM) spectra showed that the humic-like substance (HULIS) was the dominant
fraction of BrC as the other components were not measurable. The air mass
back trajectories of fire burning practices and the variations in
non-crustal potassium (K) and vanadium (V) contents in the water-soluble
aerosols during all seasons showed no measurable decrease in input of
biomass-burning sources in summer. However, there was a significant shift in
photo-resistivity of light-absorbing organic aerosols in the summer,
indicating larger removals of ultraviolet (UV) degradable BrC. This trend is
supported by laboratory UV radiation experiments on the optical property
changes of BrC and WSOC in aerosol samples. Thus, our results suggest that
the photodegradation has dominant roles in controlling the quantity and
quality of light-absorbing organic aerosols in the different seasons in the
midlatitude atmosphere.</p> |
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| ISSN: | 1680-7316 1680-7324 |