Properties of Free Tropospheric Aerosol Sampled at Pico Mountain Observatory, Azores

Improved characterization of free tropospheric aerosol optical, chemical and morphological properties is essential to further our understanding of the aerosol lifecycle, aerosol-cloud interactions and effects on radiation and climate. Free tropospheric aerosols were studied at Pico Mountain Observatory, located on top of the Pico Volcano in the Azores, Portugal (38.47°N, 28.40°W, 2225 m.a.s.l.). The station typically samples free tropospheric air masses that are transported from North America, and lays above the low marine clouds. Since 2012, during summers, we have been deploying a 3-wavelength nephelometer to measure the aerosol light scattering and backscattering fraction, a two-channel optical particle counter (for particles larger than 300 nm) and a 7-wavelength aethalometer to measure black carbon equivalent mass and iron-containing dust concentrations. In addition, a set of four high-volume samplers for the chemical analysis of aerosol, a sequential sampler and an impactor to collect aerosols for microscopy and ice nuclei analysis were deployed during the period 2012-2015. During selected ascents an instrumented backpack was also used to characterize the aerosol vertical profile from 1225 m.a.s.l. to the top of the mountain (2351 m.a.s.l.). Flexpart retroplume simulations are used to study the air mass origin, transport path and source influence.  

We will examine the optical properties of the aerosol and their potential radiative impact in terms of estimated single scatter albedo and backscatter fraction. Some morphological characteristics of the aerosols sampled at the station will also be discussed. These properties are relevant to the aerosol clouds radiative interactions especially owing to the location of the aerosol sampled at the station, typically above the marine clouds.