Physical Properties of Marine Aerosols and Influences by Meteorology during the CFOG Campaign

Atmospheric aerosols impact Earth’s radiation budget by scattering radiation and acting as cloud condensation nuclei (CCN). The CCN-activity is dependent on their size and chemical composition, whereas the cloud albedo depends on the aerosol concentration. All of these aerosol properties can be affected by meteorology. Oceans cover 70% of the earth’s surface, yet the particle emissions into the atmosphere are poorly constrained. These ocean-atmosphere interactions occur in the marine boundary layer and are important to understand in order better constrain the emissions and therefore decrease the uncertainty in weather and climate models. We explored these aerosol properties in the North Atlantic Ocean by conducting aerosol measurements on a cruise off the eastern coast of Canada for a total of 6 weeks in late summer/early fall as part of the Coastal Fog (CFOG) project. Size distributions and CCN concentrations were measured using a scanning mobility particle sizer (SMPS), aerodynamic particle sizer (APS), and a CCN counter. The SMPS and APS sized particles produced size distributions. The CCN counter subjected the particles to supersaturations varying from 0.2% to 1% and counted the number of particles that grew large enough to activate into cloud droplets. The hygroscopicity was then inferred from these measurements in order to gain insight on particle composition. Variation in these aerosol properties were compared with meteorological features. In the case of the passages of high pressure systems, there are new particles entering the marine boundary layer shown by an increase in particle concentration. A possible source of these particles is entrainment from the free troposphere into the marine boundary layer. This is suggested since some of the size distributions showed a shift from an accumulation mode dominated size distribution to an Aitken mode dominated size distribution. Further exploration into the hygroscopicity of these particles can provide insight on the composition and therefore the sources of the aerosols. The passage of other meteorological features will also be explored and their aerosol properties compared. During the cruise, a particle nucleation event and a growth event were observed. Preliminary analyses showed that with the ship being close to Nova Scotia and winds from offshore that these events may have been influenced by continental sources. The nucleation and growth events will also be examined in the context of the local meteorology data to determine how the aerosol properties changed and the possible cause of these types of events. Back trajectory analysis will be used to better understand the origin of the observed particles and therefore determine whether there was influence from the free troposphere or the surface. Back trajectory analysis will also be insightful on the different processes affecting the aerosols. The goal is to find patterns in the aerosol properties which include size distributions, particle concentrations, and hygroscopicity, as well as possible sources of the aerosols in order to better understand how ambient aerosols have the potential to influence future weather, climate, and the radiation budget.