Properties of Free Tropospheric Dust Particles above the North Atlantic Ocean

Abstract:

Improving our understanding on the lifecycle of atmospheric dust particles is critical to better model climate as well as ocean nutrients cycles. However, understanding the physiochemical properties of dust particles collected in remote regions of the atmosphere, such as the marine free troposphere, is still limited. We measured the optical properties of atmospheric particles and collected particle samples on various media for off-line analyses at the elevated Pico Mountain Observatory (2225 a.s.l.) for several summer seasons. Pico Mountain Observatory is located in the summit caldera of Pico Mountain, on Pico Island in the Azores, Portugal. The station often lays in the free troposphere above the low marine clouds. Air masses that reach Pico Mountain Observatory are transported over the North Atlantic Ocean for long periods of times, often from North America or from North Africa. We individuated dust containing plumes using the Ångström Exponent of measured scattering and attenuation coefficients at several wavelengths with a nephelometer and aethalometer. In addition, we used the information provided by a two-channel optical particle counter. The aerosol samples collected were analysed with various micro-spectroscopy techniques on a single particle basis. In particular, we will discuss the single particle elemental composition of dust particles, their mineralogy and their interaction with organic matter and sulphates during several dust events with different atmospheric aging time scales. Finally, we used retroplume simulations from the FLEXible PARTicle dispersion model (FLEXPART) to interpret the results and understand the dust source location, and transport path and time.