Ice nucleation propensity of Long-range Transport Free tropospheric aerosols over the North Atlantic

Abstract:

In this study, we collected atmospheric particles from three different events in July 2014 at the remote Pico Mountain Observatory which is located at 2225 m above sea level in the summit caldera of Pico Volcano on Pico Island in the Azores archipelago in the North Atlantic. We characterized the physicochemical properties and mixing state of collected particles using multimodal microscopy and spectroscopic techniques such as computer-controlled scanning electron microscopy with energy dispersive X-ray spectroscopy and scanning transmission X-ray microscopy with near-edge X-ray absorption fine structure spectroscopy. We investigate their ice nucleation ability using a state-of-the art ice nucleation instrument coupled with an Environmental Scanning Electron Microscope operated at temperature and relative humidity values relevant to mixed phase and cirrus clouds. We execute FLEXPART retroplume modeling to investigate transport pattern of the particles collected on different events. The physicochemical analysis shows different chemical composition and mixing state of the collected particles during different events. We also identified ice nucleating particles and found a mixture of coated dust, carbonaceous, sulfate and other particles rich in sodium and sulfur. We observed an enhancement of ice nucleation activity for the sample dominated by mineral dust. Altogether, the outcomes from this study will help to elucidate the effect of physicochemical properties and mixing state of the of long range transported free tropospheric particles on ice cloud formation.