Physico-chemical Properties of Free Tropospheric Mineral Dust at the Remote Pico Mountain Observatory, in the Azores

To improve climate modeling, it is essential to enhance our understanding of the lifecycle of atmospheric particles and their interactions with clouds and radiation, particularly in understudied remote regions such as the marine free troposphere. To address this need, we investigated atmospheric particle properties at the elevated Pico Mountain Observatory (2225 m a.s.l.) in the Azores, Portugal. The observatory typically sits above low marine clouds, sampling free-tropospheric air masses transported across the North Atlantic Ocean from North America or recirculated from North Africa. During measurement campaigns conducted in the summer months between 2012 and 2018, we characterized atmospheric particles by measuring light-scattering coefficients using a three-wavelength nephelometer, particle concentrations with a two-channel optical particle counter, and black carbon equivalent mass and iron-containing dust concentrations using a seven-wavelength aethalometer. Aerosol samples were also collected on various media for off-line bulk and single particle analysis. We used retroplume simulations from the FLEXible PARTicle dispersion model (FLEXPART) to interpret the results based on the air mass origin, transport path, transport time, and source type and region.

We investigated the physico-chemical characteristics of atmospheric particles, focusing on their optical properties and individual particle morphology and elemental makeup. In this presentation, we emphasize the properties of particles collected during episodes dominated by mineral dust transport. Specifically, we use the Ångström exponent derived from the scattering data as an indicator to identify dust events. These properties are relevant to the particles’ interactions with clouds and radiation, especially owing to the location of the atmospheric particles sampled at the station.