Scavenging of Aerosol Particles by Fog Droplets in the North Atlantic

Aerosol particles interact with water vapor in the atmosphere in different ways. They are also responsible for the formation of fog or cloud droplets at relatively lower water supersaturation than required for the droplet formation in absence of aerosol. The particles can either be scavenged by nucleation scavenging or wet scavenging. In nucleation scavenging, the aerosol particles act as nuclei aiding in the formation of water droplets while the interstitial particles are scavenged by wet scavenging by the fog or rain droplets. We analyse the particle size distributions before, during and after the fog events. This study attempts to establish the association between the droplet size distributions and scavenging of aerosol particles by the fog droplets by analyzing the particle size distribution. The underlying assumption in this study is that the aerosol size distribution remained the same despite the fog. The measurements were carried out onboard RV Hugh Sharp over the Atlantic Ocean and in Halifax, Nova Scotia, Canada in summer of 2018 and 2019, respectively. The particle size distributions were measured using scanning mobility and aerodynamic particle sizers while the fog droplet concentrations were measured using a fog droplet monitor. The particles sizing instruments were operated inline with a homebuilt inlet which segregates between droplets and particles while the fog droplet monitor was operated independently adjacent to the inlet. The preliminary results indicate that the coarse mode particles are scavenged by nucleation scavenging in the initial phase of the fog event followed by the accumulation mode particles. The results of this study can be used in fog models as well as air quality prediction models.