Free Tropospheric North Atlantic Aerosols Observed at the Pico Mountain Observatory

Description

Pico Mountain Observatory is located in the North Atlantic ~3900 km east of North America (38°28’15’’N; 28°24’14’’W) at an elevation of 2225 m a.s.l. in the summit caldera of the Pico Volcano on Pico Island in the Azores, Portugal. Far from large orographic systems and above the marine boundary layer during most times in the summer, the observatory is an ideal location to sample and analyze the characteristics of aerosols in the North Atlantic free troposphere. Air masses reaching the site predominantly originate from the North American continent, although episodes of transport from North Africa, Europe and other locations occur occasionally. Aerosols from several different sources such as anthropogenic pollution, biomass burning, sea-salt and desert dust are injected into the free troposphere and long-range transported over the Ocean contributing to the aerosol measured at the site. Therefore, observations at the Pico site allow study of a variety of aerosols types with various chemical composition, size, morphology, optical properties and mixing, after aging and cloud processing during transport. Black Carbon (BC) concentrations have been measured at the site during the summer months since 2001 using a 7-wavelength aethalometer. In 2012, new aerosol instrumentation was added to the Observatory. A 3-wavelength nephelometer measures total scattering and backscattering fraction, an optical particle counter measures particle concentrations in two channels above 300 nm. Aerosol samples were collected on Nucleopore membranes, TEM grids, and quartz filters (using high-volume samplers). The samples were analyzed for organic and elemental carbon (OC and EC, respectively) using a Sunset OCEC analyzer, water-soluble organic carbon (WSOC) molecular formulas using ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), water-soluble inorganic anions and cations using ion chromatography, and morphology and mixing state using electron microscopy (SEM and TEM). In this presentation we discuss specific periods of interest during the summer of 2012, to study aerosol mixing and morphology, BC aging, aerosol optical properties and chemical composition. The aerosol characterization is conducted together with collocated measurements of trace gases, and meteorological parameters.