| Summary: | Marine aerosols play an important role in earth’s climate, but their effects remain highly uncertain due to a poor understanding of their sources, properties, and atmospheric processing, partly due to limited measurements. The Coastal-Fog (C-FOG) study investigated the processes controlling the formation and properties of fog in the North Atlantic Ocean. As part of this study, aerosol particle size distributions and chemical composition were measured off the shore of the northeastern United States and Atlantic Canada, and used to investigate the sources and processes affecting the observed aerosols. Processed marine air during the study was characterized by single and bi-modal aerosol size distributions. Aerosols in the port city of St. John’s, Newfoundland reflected local emissions built up due to poor ventilation, whereas aerosols in Halifax, Nova Scotia were lower in concentration because the harbour is more spread out. Finally, two particle growth events were observed. The first event captured the appearance of 10 nm particles that grew to 30 nm over 4 h. These aerosols appeared to be newly formed in the upper portion of the boundary layer with influence from the free troposphere before subsiding to the surface. In the second event, 45 nm particles grew to 70 nm over 8 h. The growth of these aerosols was most likely due to the direct condensation of organic vapours emitted from boreal forests and/or the ocean. Our observations provide important insight into the processes affecting marine aerosols and highlight the crucial role of boundary layer meteorology.
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