10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Seasonal Variability of Aerosol Optical and Physical Properties from the Eastern North Atlantic (ENA) Aerosol Observing System (AOS) during 2016 and 2017
FRANCESCA GALLO, Allison Aiken, Connor Flynn, Annette Koontz, Jian Wang, Guangjie Zheng, Stephen Springston, Chongai Kuang, Janek Uin, Eduardo Azevedo, Kim Nitschke, Los Alamos National Lab
Abstract Number: 1426 Working Group: Remote/Regional Atmospheric Aerosol
Abstract In the present study we assess the seasonal variability of aerosol optical and physical properties at the Eastern North Atlantic (ENA) Atmospheric Radiation Measurement (ARM) Facility. The ENA site is located in the remote Azores archipelago and is subject to strong meteorological variability during the year. Consequently, aerosol composition and concentration are affected by these meteorological variations. Especially, the combination of midlatitude, tropical and extratropical cyclones and strong surface wind speeds affect the Region during the winter, leading to the formation of coarse mode aerosols (e.g. sea salt), meanwhile the subtropical Azores high pressure system and diminished surface wind speeds in the summer lead to the production of fine mode aerosols. Here we show the seasonal variability of aerosol absorption, scattering and extinction coefficients (Babs, Bsca and Bext) and intensive aerosol properties of light absorption, scattering and extinction Angstrom exponents (AAE, SAE and EAE) and single scatter albedo (SSA) for submicron (PM1) and sub-10 µm (PM10) diameter size cuts during the years 2016 and 2017 at ENA. Data were obtained through continuous measurement with the Aerosol Observing System (AOS) equipped with a 3 wavelength Nephelometer (450, 550, 700 nm) and PSAP (464, 529, 648 nm). Results indicate a seasonal trend in the PM1 and PM10 aerosol optical properties during the period of study with the exception of PM10 SSA (0.90 ± 0.09). Total aerosol Babs is dominated by the PM1 fraction throughout the year (~60% of the total Babs due to the submicron) while Bsca is dominated by the supermicron species (~ 70% of the total Bsca due to the PM10). However, both Babs and Bsca are highest in the winter and lower in the summer ranging respectively from seasonal averages of 0.46 – 0.70 Mm-1 and 5.35 – 7.38 Mm-1 in PM1 and 0.77 – 1.15 Mm-1 and 14.8 – 26.57 Mm-1 in PM10. Bext shows seasonal variability in the PM10 fraction (seasonal averages ranging from 12.71 – 19.65 Mm-1). Intensive aerosol properties also indicate a seasonal trend: while AAE is highest in the winter (seasonal averages ranging from 0.85 – 1.09 in PM1 and from 0.96 – 1.12 in PM10), SAE is highest in the summer (seasonal averages ranging from 1.88 – 1.18 in PM1 and from 0.39 – 0.89 in PM10). Combination of AAE and SAE spectral variability in PM1 reveals the dominance of small particle diameters in the summer and the presence of mixed absorption species, dominated by soot in the winter. Changes in both meteorological conditions and emission source through the year could explain these variations. This hypothesis is also supported by the evaluation of wind speed and direction and total aerosol number concentration. Future investigations concerning aerosol size distributions from the UHSAS and chemical composition from the ACSM at ENA will be used to support our findings.