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Source‐diagnostic dual‐isotope composition and optical properties of water‐soluble organic carbon and elemental carbon in the South Asian outflow intercepted over the Indian Ocean
Author(s) -
Bosch Carme,
Andersson August,
Kirillova Ele.,
Budhavant Krishnakant,
Tiwari Suresh,
Praveen P. S.,
Russell Lynn M.,
Beres Nicholas D.,
Ramanathan Veerabhadran,
Gustafsson Örjan
Publication year - 2014
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2014jd022127
Subject(s) - radiative forcing , total organic carbon , carbon fibers , aerosol , environmental chemistry , environmental science , dissolved organic carbon , atmospheric sciences , isotopes of carbon , outflow , chemistry , climatology , oceanography , physics , geology , materials science , organic chemistry , composite number , composite material
The dual carbon isotope signatures and optical properties of carbonaceous aerosols have been investigated simultaneously for the first time in the South Asian outflow during an intensive campaign at the Maldives Climate Observatory on Hanimaadhoo (MCOH) (February and March 2012). As one component of the Cloud Aerosol Radiative Forcing Dynamics Experiment, this paper reports on the sources and the atmospheric processing of elemental carbon (EC) and water‐soluble organic carbon (WSOC) as examined by a dual carbon isotope approach. The radiocarbon (Δ 14 C) data show that WSOC has a significantly higher biomass/biogenic contribution (86 ± 5%) compared to EC (59 ± 4%). The more 13 C‐enriched signature of MCOH‐WSOC (−20.8 ± 0.7‰) compared to MCOH‐EC (−25.8 ± 0.3‰) and megacity Delhi WSOC (−24.1 ± 0.9‰) suggests that WSOC is significantly more affected by aging during long‐range transport than EC. The δ 13 C‐Δ 14 C signal suggests that the wintertime WSOC intercepted over the Indian Ocean largely represents aged primary biomass burning aerosols. Since light‐absorbing organic carbon aerosols (Brown Carbon (BrC)) have recently been identified as potential contributors to positive radiative forcing, optical properties of WSOC were also investigated. The mass absorption cross section of WSOC (MAC 365 ) was 0.5 ± 0.2 m 2 g −1 which is lower than what has been observed at near‐source sites, indicating a net decrease of WSOC light‐absorption character during long‐range transport. Near‐surface WSOC at MCOH accounted for ~1% of the total direct solar absorbance relative to EC, which is lower than the BrC absorption inferred from solar spectral observations of ambient aerosols, suggesting that a significant portion of BrC might be included in the water‐insoluble portion of organic aerosols.