Origin of water-soluble organic aerosols at the Maïdo high-altitude observatory, Réunion Island, in the tropical Indian Ocean
Year: 2021
Type: article
Abstract: 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 ∘ S, 55.4 ∘ 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 (∼ 45 ± 17 %) during the wet season (15 March–23 April). On the other hand, sulfate dominated (∼ 77 ± 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 (∼ 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.
Institutions: Hokkaido University, Institute of Low Temperature Science, Hokkaido University, Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Centre National de la Recherche Scientifique, University of Reunion Island, Laboratoire de l'Atmosphère et des Cyclones, Université Clermont Auvergne, Laboratoire de Météorologie Physique, Institut polytechnique de Grenoble, Institut des Géosciences de l'Environnement, Institut de Recherche pour le Développement, Royal Belgian Institute for Space Aeronomy, Ghent University
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,725
Awards: Organic nitrogen aerosol in the marine atmosphere: Which factors control the amount of organic nitrogen in marine microbial activity?, Origin and formation mechanisms of organic nitrogen aerosols derived from biogenic terpenes, Chemical Coupling of Halogens and Oxygenated VOC (Volatile Organic Compounds): Observations, Experiments and Modeling, G8187199458, Collaborative Research: TI3GER--Technological Innovation Into Iodine and Gv-aircraft Environmental Research
OpenAlex ID: W3171600543