Entrainment of Long-Range Transported Aerosols in the Marine Boundary Layer in the Azores

Atmospheric aerosols significantly impact Earth's radiation budget by interacting with solar radiation and affecting the properties of clouds. Aerosol transport over long horizontal distances in the free troposphere to remote regions such as the Azores in the mid-North Atlantic ocean has been routinely observed and extensively studied. However, free-tropospheric long-range transported aerosols like Saharan desert dust or North-American biomass burning carbonaceous particles can also be transported vertically, contributing to the aerosol loading and the local atmospheric and cloud properties in the Azores. We analyzed data from two sites in the Azores: (a) Pico mountain observatory at 2225 m a.s.l. and (b) Eastern North Atlantic (ENA) DOE-ARM facility, near sea level for periods between 2014 to 2017. The two sites are within a horizontal distance of 70 km. Pico generally lies in the lower free troposphere, while ENA lies in the lower marine boundary layer. These sites provide a unique opportunity to analyze aerosols at two different elevations and study vertical aerosol exchange processes. Continuous aerosol intensive properties (e.g., the wavelength dependence of light scattering and absorption) at the two sites were used to detect potential events of vertical aerosol transport between the free troposphere and the marine boundary layer. We used additional aerosol data from satellite, ground, and aircraft instruments for various case studies to further understand these events' nature and investigate the statistical and mechanistic connections with concurrent atmospheric conditions. Monthly, diurnal, and yearly variations and frequency and length of these events will be discussed. We will also discuss links between cloud condensation nuclei concentrations at the two sites and the properties of the stratocumulus clouds in the region during these events.