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.
Source apportionment of the organic aerosol over the Atlantic Ocean from 53° N to 53° S: significant contributions from marine emissions and long-range transport
