10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Molecular and Physical Characteristics of Aerosol at a Remote Marine Free Troposphere Site: Implications for Atmospheric Aging
SIMEON SCHUM, Bo Zhang, Katja Dzepina, Swarup China, Paulo Fialho, Claudio Mazzoleni, Lynn Mazzoleni, Michigan Technological University
Abstract Number: 1591 Working Group: Remote/Regional Atmospheric Aerosol
Abstract Marine regions cover a large fraction of the Earth’s surface. In these regions, long range transported aerosol can play a key role on the Earth radiative balance by interacting with clouds and solar radiation. However, free tropospheric aerosol over the ocean are not well characterized due to the challenges of sampling in these remote areas. We analyzed the molecular and physical characteristics of long-range transported aerosol samples collected at the Pico Mountain Observatory (38° 28’ 15’’ N; 28° 24’ 14’’ W, 2225 m above mean sea level) in the North Atlantic Ocean. The Observatory is located in the marine free troposphere on Pico Island in the Azores archipelago, making it an excellent site for the study of aged organic aerosol with minimal influence of local emission sources. Specific samples were selected for detailed molecular study based on (1) elevated organic carbon concentrations and (2) FLEXPART simulations with the goal to capture pollution events of different origins. Water-soluble organic aerosol extracts were then analyzed using ultrahigh resolution mass spectrometry (R > 200,000) in order to elucidate their molecular characteristics. Thousands of molecular formulas were assigned to each of the individual samples. On average ~60 % of the molecular formulas contained only carbon, hydrogen, and oxygen atoms (CHO), ~30 % contained nitrogen (CHNO), and ~10 % contained sulfur (CHOS). In general, samples transported through the free troposphere were less oxidized than those transported through the boundary layer. Despite their longer residence times, average oxygen to carbon (O/C) ratios of less than 0.5 were observed for the free tropospheric aerosol, compared to O/C ratios greater than 0.5 for those transported in the boundary layer. Using the extracted ambient temperature and relative humidity from the FLEXPART-GFS/FNL simulations, the phase state of the water-soluble organic aerosol molecular species was estimated for up to 5 days before sampling. The low temperature and relative humidity in the free troposphere predict a solid phase for the organic aerosol, which likely increased its resistance to oxidation. The specific molecular differences in the overall oxidation between the free tropospheric transported aerosol and the boundary layer transported aerosol are presented, as well as the potential for aqueous phase oxidation and differences in the aerosol phase state.