Characterizing Atmospheric Aerosols off the Atlantic Canadian Coast During C-FOG

Marine aerosols play an important role in the 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 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 north-eastern 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 bimodal aerosol size distributions. Aerosols in the port city of St. John’s, Newfoundland likely reflected local emissions built up due to poor ventilation, whereas aerosols observed in Halifax, Nova Scotia were likely affected by transport, cloud processing and precipitation. 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. Our observations provide important insight into the processes affecting marine aerosols and highlight the crucial role of boundary-layer meteorology.