Chemical composition and size distributions of coastal aerosols observed on the US East Coast

Characterization of coastal aerosols is important to the study of the atmospheric input of nutrients to the adjacent marine and the ocean ecosystems. Over a land–ocean transition zone, however, aerosol composition could be strongly modified by anthropogenic emissions and transport processes. This work focuses on examining aerosol properties, in particular chemical composition, particle-size distributions and iron (Fe) solubility, over the US East Coast, an important boundary for the transport of continental substances from North America to the North Atlantic Ocean. Fourteen sets of bulk aerosol samples and three sets of size-segregated aerosol samples were collected in southern New Jersey on the US East Coast during 2007 and 2008. Samples were analyzed by IC, ICP-MS and UV spectroscopy. The major chemical components were nitrate, non-sea-salt sulfate (NSS-sulfate), ammonium, sodium and chloride, accounting for ∼ 70% of the total mass. A typical bimodal mass-size distribution was observed, with the major peak from 0.36 µm to 0.56 µm and the minor one from 3.6 µm to 5.6 µm in diameters. Different individual components showed different mass-size distributions. Pollution-derived substances, such as vanadium and NSS-sulfate of non-biogenic origin, were mostly in the fine mode, while crustal elements, such as aluminum and iron, were mainly in the coarse mode. At this location, the concentrations of soluble ferrous species (Fe(II)s) in aerosols ranged from 50 to 518 pmol m− 3, accounting for ∼ 17% of the total Fe (FeT) mass in bulk samples. The average Fe solubility observed at this location was 18%, higher than those over remote oceans. Fe solubility showed an inverse correlation with FeT concentrations, which could be the result of different particle sizes. In addition, high Fe solubility was associated with high molar ratios of NSS-sulfate to FeT and oxalate to FeT, indicating that inorganic and organic acidic components and anthropogenic emissions may highly affect Fe solubility in this region.