Chemical characterization of marine sub-micrometer aerosol particles during the MERIAN cruise MSM18/3 from the Cape Verde island Sao Vicente to Gabun (Atlantic Ocean)

Sub-micron marine aerosol particles (PM1) were collected during the MERIAN cruise MSM 18/3 between 22 June 2011 and 21 July 2011 from the Cape Verde island Sao Vicente to Gabun crossing the tropical Atlantic Ocean and passing equatorial upwelling areas. According to air mass origin and chemical composition of the aerosol particles, three main regimes could be established. Aerosol particles in the first part of the cruise were mainly of marine origin, in the second part was marine and slightly biomass burning influenced (increasing tendency) and in the in last part of the cruise, approaching the African mainland, biomass burning influences became dominant. Generally aerosols were dominated by sulfate (caverage = 1.99 µg/m**3) and ammonium ions (caverage = 0.72 µg/m**3) that are well correlated and slightly increasing along the cruise. High concentrations of water insoluble organic carbon (WISOC) averaging 0.51 µg/m**3 were found probably attributed to the high oceanic productivity in this region. Water soluble organic carbon (WSOC) was strongly increasing along the cruise from concentrations of 0.26 µg/m**3 in the mainly marine influenced part to concentrations up to 3.3 µg/m**3 that are probably caused by biomass burning influences. Major organic constituents were oxalic acid, methansulfonic acid (MSA) and aliphatic amines. MSA concentrations were quite constant along the cruise (caverage = 43 ng/m**3). While aliphatic amines were more abundant in the first mainly marine influenced part with concentrations of about 20 ng/m**3, oxalic acid showed the opposite pattern with average concentrations of 12 ng/m**3 in the marine and 158 ng/m**3 in the biomass burning influenced part. The alpha dicarbonyl compounds glyoxal and methylglyoxal were detected in the aerosol particles in the low ng/m**3 range and followed oxalic acid closely. MSA and aliphatic amines accounted for biogenic marine (secondary) aerosol constituents whereas oxalic acid and the alpha dicarbonyl compounds were believed to result mainly from biomass burning. N-alkane concentrations increased along the cruise from 0.81 to 4.66 ng/m**3, PAHs and hopanes were abundant in the last part of the cruise (caverage of PAHs = 0.13 ng/m**3, caverage of hopanes = 0.19 ng/m**3). Levoglucosan was identified in several samples of the last part of the cruise in concentrations around 2 ng/m**3, pointing to (aged) biomass burning influences. The investigated organic compounds could explain 9.5% of WSOC in the mainly marine influenced part (dominating compounds: aliphatic amines and MSA) and 2.7% of WSOC in the biomass burning influenced part (dominating compound: oxalic acid) of the cruise.亚微米级海洋气溶胶颗粒物（PM1）于2011年6月22日至7月21日期间的MERIAN航次MSM 18/3中采集，采样路线从佛得角圣维森特岛出发，横跨热带大西洋并途经赤道上升流区，最终抵达加蓬。依据气团来源与气溶胶颗粒物的化学组成，可将本次航次的气溶胶划分为三种主要类型：航次第一阶段的气溶胶主要源自海洋；第二阶段兼具海洋来源与轻度生物质燃烧影响（影响程度呈上升趋势）；而在航次最后阶段，当航船接近非洲大陆时，生物质燃烧的影响占据主导地位。 总体而言，气溶胶以硫酸盐（平均浓度为1.99 μg/m³）与铵离子（平均浓度为0.72 μg/m³）为主要组分，二者相关性较强，且浓度在航次过程中呈小幅上升趋势。检测到高浓度的水不溶性有机碳（WISOC），其平均浓度为0.51 μg/m³，该现象大概率与该区域较高的海洋生产力相关。水溶性有机碳（WSOC）的浓度在航次中显著上升：在以海洋影响为主的阶段，其浓度为0.26 μg/m³，而在受生物质燃烧影响的阶段，浓度最高可达3.3 μg/m³，这一变化大概率由生物质燃烧影响所导致。主要的有机组分包括草酸、甲磺酸（MSA）以及脂肪胺。甲磺酸（MSA）的浓度在整个航次中相对稳定，平均浓度为43 ng/m³。脂肪胺在以海洋影响为主的第一阶段含量更高，浓度约为20 ng/m³；而草酸则呈现相反的分布模式：在海洋影响阶段其平均浓度为12 ng/m³，在受生物质燃烧影响的阶段则升至158 ng/m³。α-二羰基化合物乙二醛与甲基乙二醛在气溶胶颗粒物中被检出，浓度处于ng/m³级别，且其分布模式与草酸高度一致。甲磺酸与脂肪胺属于生源性海洋（二次）气溶胶组分，而草酸与α-二羰基化合物则被认为主要来源于生物质燃烧。正构烷烃的浓度在航次中从0.81 ng/m³上升至4.66 ng/m³；多环芳烃（PAHs）与藿烷在航次最后阶段含量较高，二者的平均浓度分别为0.13 ng/m³与0.19 ng/m³。在航次最后阶段的部分样品中检出了左旋葡聚糖，浓度约为2 ng/m³，这表明存在（老化的）生物质燃烧影响。本次研究中检出的有机化合物，可解释以海洋影响为主阶段中9.5%的水溶性有机碳（WSOC）（主要贡献组分为脂肪胺与甲磺酸），以及受生物质燃烧影响阶段中2.7%的水溶性有机碳（WSOC）（主要贡献组分为草酸）。