Particle phase-state variability in the North Atlantic free troposphere during summertime determined by different atmospheric transport patterns and sources

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Cheng, Zezhen, Morgenstern, Megan, Zhang, Bo, Fraund, Matthew, Lata, Nurun Nahar, Brimberry, Rhenton, Marcus, Matthew A., Mazzoleni, Lynn, Fialho, Paulo, Henning, Silvia, Wehner, Birgit, Mazzoleni, Claudio, China, Swarup
• Language: unknown
• Published: 2023
• Subjects: Mount Pico; North Atlantic
• Online Access: http://www.osti.gov/servlets/purl/1958533; https://www.osti.gov/biblio/1958533; https://doi.org/10.5194/acp-22-9033-2022

Free tropospheric aerosol particles have important but poorly constrained climate effects due to transformations of their physicochemical properties during long-range transport. In this study, we investigated the chemical composition and provided an overview of the phase state of individual particles that have been long-range transported over the North Atlantic Ocean in June and July 2014, 2015, and 2017 to the Observatory of Mount Pico (OMP), in the Azores. OMP is an ideal site for studying long-range transported free tropospheric particles with negligible influence from local emissions and rare contributions from the boundary layer. We used the FLEXible PARTicle Lagrangian particle dispersion model (FLEXPART) to determine the origin and transport trajectories of sampled air masses and found that most originated from North America and recirculated over the North Atlantic Ocean. The FLEXPART analysis show that the sampled air masses were highly aged (average plume age >10 days). Size-resolved chemical compositions of individual particles were probed using computer-controlled scanning electron microscopy with an energy dispersive X-ray spectrometer (CCSEM-EDX) and scanning transmission X-ray microscopy with near-edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS). CCSEM-EDX results show that the most abundant particle types were carbonaceous (~29.9 to 82.0 %), sea salt (~0.3 to 31.6 %), and sea salt with sulfate (~2.4 to 31.5 %). We used a tilted stage interfaced within an Environmental Scanning Electron Microscope (ESEM) to determine the phase state of individual submicron particles. We found that most particles (~47 to 99 %) were in the liquid state at the time of collection due to inorganic inclusions. Moreover, we also observed a substantial fraction of solid and semisolid particles (~0 to 30 % and ~1 to 42 %, respectively) during different transport patterns/events, reflecting the particles’ phase state variability for different atmospheric transport events and sources. Combining phase state ...