Abstract
Abstract. Marine aerosol particles are an important part of the natural aerosol systems and might have a significant impact on the global climate and biological cycle. It is widely accepted that truly pristine marine conditions are difficult to find over the ocean. However, the influence of continental and anthropogenic emissions on the marine boundary layer (MBL) aerosol is still less understood and non-quantitative, causing uncertainties in the estimation of the climate effect of marine aerosols. This study presents a detailed chemical characterization of the MBL aerosol as well as the source apportionment of the organic aerosol (OA) composition. The data set covers the Atlantic Ocean from 53∘ N to 53∘ S, based on four open-ocean cruises in 2011 and 2012. The aerosol particle composition was measured with a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), which indicated that sub-micrometer aerosol particles over the Atlantic Ocean are mainly composed of sulfates (50 % of the particle mass concentration), organics (21 %) and sea salt (12 %). OA has been apportioned into five factors, including three factors linked to marine sources and two with continental and/or anthropogenic origins. The marine oxygenated OA (MOOA, 16 % of the total OA mass) and marine nitrogen-containing OA (MNOA, 16 %) are identified as marine secondary products with gaseous biogenic precursors dimethyl sulfide (DMS) or amines. Marine hydrocarbon-like OA (MHOA, 19 %) was attributed to the primary emissions from the Atlantic Ocean. The factor for the anthropogenic oxygenated OA (Anth-OOA, 19 %) is related to continental long-range transport. Represented by the combustion oxygenated OA (Comb-OOA), aged combustion emissions from maritime traffic and wild fires in Africa contributed, on average, a large fraction to the total OA mass (30 %). This study provides the important finding that long-range transport was found to contribute averagely 49 % of the submicron OA mass over the Atlantic Ocean. This is almost equal to that from marine sources (51 %). Furthermore, a detailed latitudinal distribution of OA source contributions showed that DMS oxidation contributed markedly to the OA over the South Atlantic during spring, while continental-related long-range transport largely influenced the marine atmosphere near Europe and western and central Africa (15∘ N to 15∘ S). In addition, supported by a solid correlation between marine tracer methanesulfonic acid (MSA) and the DMS-oxidation OA (MOOA, R2>0.85), this study suggests that the DMS-related secondary organic aerosol (SOA) over the Atlantic Ocean could be estimated by MSA and a scaling factor of 1.79, especially in spring.
Highlights
As one of the most important natural aerosol systems at the global level, the marine aerosol plays a significant role in the global radiation budget through both direct and indirect climate effects, as well as playing a role in biogeochemical cycling (O’Dowd and De Leeuw, 2007; Saltzman, 2009)
This study presents the physicochemical measurements of the marine boundary layer (MBL) aerosol over the Atlantic Ocean conducted during www.atmos-chem-phys.net/18/18043/2018/
Considering that organics are an important constituent of the sub-micrometer aerosol and contain a large number of compounds from different sources and processes, source apportionment of organic aerosol (OA) was performed using the Positive matrix factorization (PMF) method
Summary
As one of the most important natural aerosol systems at the global level, the marine aerosol plays a significant role in the global radiation budget through both direct and indirect climate effects, as well as playing a role in biogeochemical cycling (O’Dowd and De Leeuw, 2007; Saltzman, 2009). Secondary marine aerosol particles are chemically produced from atmospheric reactions of gases emitted by organisms in the ocean (Charlson et al, 1987). As one of the most well-known biological gases, dimethyl sulfide (DMS), emitted by marine phytoplankton, can be oxidized to eventually form sulfate and methanesulfonic acid (MSA) in the particulate phase (Ayers and Gillett, 2000; Bates et al, 1987; Charlson et al, 1987; Gondwe et al, 2003; Hertel et al, 1994; Shiro Hatakeyama, 1985; von Glasow and Crutzen, 2004). The chemical and physical properties of the marine aerosol are still poorly understood
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