Source apportionment of the submicron organic aerosols over the Atlantic Ocean from 53dtN to 53dtS using HR-ToF-AMS

Abstract. The marine aerosol is one of the most important natural aerosol systems and can significantly impact the global climate as well as biological cycle. A series of measurements during four open-ocean cruises in 2011 and 2012 over the Atlantic from 53° N to 53° S were conducted to reveal the physical and chemical properties of the marine boundary layer (MBL) aerosol and its seasonality. Chemical composition of the submicron particles was obtained using the on-line techniques High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) as well as from offline high-volume PM 1 filter samples with a sampling time of 24 hours. Our measurements show that the MBL aerosol particle mass is controlled by sulfate (50 %), followed by organics (21 %), sea salt (12 %), ammonium (9 %), Black Carbon (BC, 5 %) and nitrate (3 %). Only sulfate exhibits pronouncedly seasonal dependency, while no such trend was observed in other species. Source apportionment of the organic fraction was performed using Positive Matrix Factorization (PMF). Five factors were identified, including three marine sources and two non-marine sources. Marine sources are linked to primary production (19 % of total organic aerosol (OA) mass), marine dimethylsulfide (DMS)-oxidation (16 %), and amine-related secondary formation (16 %). The other two OA components are attributed to continental outflow (19 %) and aged ship exhausts – biomass burning emissions (30 %). Our study indicates that, on average, non-marine sources nearly have the equal importance to the Atlantic aerosols comparing with the marine sources, respectively contributing 49 % and 51 % to the total OA mass loadings. The South Atlantic atmosphere is found to be less polluted than the North according to our source analysis. Detailed latitudinal distribution of OA sources showed that DMS oxidation contributes remarkably to the MBL aerosol over the South Atlantic during spring, while continental pollutants largely contaminate the marine atmosphere when near the west and middle Africa (15° N~15° S) as well as Europe. Based on our measurements, SOA produced from DMS oxidation over the Atlantic can be estimated as MSA mass concentration times a scaling factor 1.79 for spring season, which is derived from the strong correlation (R 2 u003e 0.85) between MSA and DMS-oxidation OA component.