Current parametrization of cloud–aerosol interactions of nascent sea-spray aerosols (SSA) in the climate models is hampered by our limited understanding of the constituents of organic aerosols. We investigated here the mass concentrations, molecular distributions, and relative abundances of hydroxy fatty acids (FAs), ubiquitous lipid compounds in the SSA collected over the western Pacific Ocean (35°N–40°S). Detectable levels of methanesulfonic acid (an oxidation product of dimethyl sulfide) and high enrichment factors of Mg2+ and Ca2+ relative to Na+ emphasize the impact of the marine biological activity on the organic fraction of SSA. The molecular distributions of β-hydroxy FAs with characteristic “odd-C” predominance (C9 > C10 and C11 > C12) among short-chain homologues (

No abstract

Black carbon (BC) aerosols affect climate, especially in high aerosol loading regions such as South Asia. A key uncertainty for the climate effects of BC is the evolution of light‐absorbing properties in the atmosphere. Here, we present a year‐round comparison of the mass absorption cross section (MAC; 678 nm) of BC in air (PM10) and rain, for samples collected at the Maldives Climate Observatory at Hanimaadhoo. We develop a filter‐loading correction scheme for estimating BC absorption on filters used in high‐volume samplers. The year‐round average MAC678 of BC in the rain is almost twice (13.3 ± 4.2 m2/g) compared to the PM10 aerosol (7.2 ± 2.6 m2/g). A possible explanation is the elevated ratio of organic carbon (OC) to BC observed in rain particulate matter (9.4 ± 6.3) compared to in the aerosols (OC/BC 2.6 ± 1.4 and water‐insoluble organic carbon/BC 1.2 ± 0.8), indicating a coating‐enhancement effect. In addition to BC, we also investigated the MAC365 of water‐soluble brown carbon in PM10 (0.4 ± 0.4 m2/g, at 365 nm). In contrast to BC, MAC365brown carbon relates to air mass history, showing higher values for samples from air originating over the South Asian landmass. Furthermore, calculated washout ratios are much lower for BC compared to OC and inorganic ions such as sulfate, implying a longer atmospheric lifetime for BC. The wet deposition flux for BC during the high loading winter was 3 times higher than during the wet summer, despite much less precipitation in the winter.