Origin of water-soluble organic aerosols at the Maïdo high-altitude observatory, Réunion Island, in the tropical Indian Ocean
<p>The tropical and subtropical Indian Ocean (IO) is expected to be a significant source of water-soluble organic aerosols (WSOAs), which are important factors relevant to cloud formation of aerosol particles. Current atmospheric numerical models significantly underestimate the budget of organ...
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| Autores principales: | , , , , , , , , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Copernicus Publications
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/f5a0066c985847a0a335f0817462900e |
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| Sumario: | <p>The tropical and subtropical Indian Ocean (IO) is
expected to be a significant source of water-soluble organic aerosols
(WSOAs), which are important factors relevant to cloud formation of aerosol
particles. Current atmospheric numerical models significantly underestimate
the budget of organic aerosols and their precursors, especially over
tropical oceans. This is primarily due to poor knowledge of sources and the
paucity of observations of these parameters considering spatial and temporal
variation over the tropical open ocean. To evaluate the contribution of
sources to WSOA
as well as their formation processes, submicrometer aerosol
sampling was conducted at the high-altitude Maïdo observatory
(21.1<span class="inline-formula"><sup>∘</sup></span> S, 55.4<span class="inline-formula"><sup>∘</sup></span> E; 2160 m a.s.l.), located on the remote
island of La Réunion in the southwest IO. The aerosol samples were
continuously collected during local daytime and nighttime, which
corresponded to the ambient conditions of the marine boundary layer (MBL)
and free troposphere (FT), respectively, from 15 March to 24 May 2018.
Chemical analysis showed that organic matter was the dominant component of
submicrometer water-soluble aerosol (<span class="inline-formula">∼</span> 45 <span class="inline-formula">±</span> 17 %)
during the wet season (15 March–23 April). On the other hand, sulfate
dominated (<span class="inline-formula">∼</span> 77 <span class="inline-formula">±</span> 17 %) during the dry season (24 April–24 May),
most of which was attributable to the effect of volcanic
eruption. Measurements of the stable carbon isotope ratio of water-soluble
organic carbon (WSOC) suggested that marine sources contributed
significantly to the observed WSOC mass in both the MBL and the FT in the
wet season, whereas a mixture of marine and terrestrial sources contributed
to WSOC in the dry season. The distinct seasonal changes in the dominant
source of WSOC were also supported by Lagrangian trajectory analysis.
Positive matrix factorization analysis suggested that marine secondary organic aerosol (OA)
dominantly contributed to the observed WSOC mass (<span class="inline-formula">∼</span> 70 %)
during the wet season, whereas mixtures of marine and terrestrial sources
contributed during the dry season in both MBL and FT. Overall, this study
demonstrates that the effect of marine secondary sources is likely important
up to the FT in the wet season, which may affect cloud formation as well as
direct radiative forcing over oceanic regions.</p> |
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