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Title:Molecular and physical characteristics of aerosol at a remote free troposphere site : implications for atmospheric aging
Authors:Schum, Simeon K. (Author)
Zhang, Bo (Author)
Džepina, Katja (Author)
Fialho, Paulo (Author)
Mazzoleni, Claudio (Author)
Mazzoleni, Lynn R. (Author)
Files:This document has no files. This document may have a phisical copy in the library of the organization, check the status via COBISS. Link is opened in a new window
Language:English
Work type:Unknown ()
Tipology:1.01 - Original Scientific Article
Organization:UNG - University of Nova Gorica
Abstract:Aerosol properties are transformed by atmospheric processes during long-range transport and play a key role in the Earth’s radiative balance. To understand the molecular and physical characteristics of free tropospheric aerosol, we studied samples collected at the Pico Mountain Observatory in the North Atlantic. The observatory is located in the marine free troposphere at 2225m above sea level, on Pico Island in the Azores archipelago. The site is ideal for the study of long-range-transported free tropospheric aerosol with minimal local influence. Three aerosol samples with elevated organic carbon concentrations were selected for detailed analysis. FLEXPART retroplumes indicated that two of the samples were influenced by North American wildfire emissions transported in the free troposphere and one by North American outflow mainly transported within the marine boundary layer. Ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry was used to determine the detailed molecular composition of the samples. 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). The molecular formula compositions of the two wildfire-influenced aerosol samples transported mainly in the free troposphere had relatively low average O=C ratios (0:480:13 and 0:450:11) despite the 7–10 days of transport time according to FLEXPART. In contrast, the molecular composition of the North American outflow transported mainly in the boundary layer had a higher average O=C ratio (0:570:17) with 3 days of transport time. To better understand the difference between free tropospheric transport and boundary layer transport, the meteorological conditions along the FLEXPART simulated transport pathways were extracted from the Global Forecast System analysis for the model grids. We used the extracted meteorological conditions and the observed molecular chemistry to predict the relative-humidity-dependent glass transition temperatures (Tg) of the aerosol components. Comparisons of the Tg to the ambient temperature indicated that a majority of the organic aerosol components transported in the free troposphere were more viscous and therefore less susceptible to oxidation than the organic aerosol components transported in the boundary layer. Although the number of observations is limited, the results suggest that biomass burning organic aerosol injected into the free troposphere is more persistent than organic aerosol in the boundary layer having broader implications for aerosol aging.
Keywords:secondary organic aerosols, brown carbon, particle dispersion model, ultrahigh-resolution FT-ICR MS, Pico Mountain Observatory
Year of publishing:2018
Number of pages:str. 14017-14036
Numbering:iss. 19, Vol. 18
COBISS_ID:59029507 Link is opened in a new window
UDC:53
ISSN on article:1680-7316
URN:URN:SI:UNG:REP:CVDYKDRQ
DOI:10.5194/acp-18-14017-2018 Link is opened in a new window
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Title:Atmospheric chemistry and physics
Shortened title:Atmos. chem. phys.
Publisher:European Geophysical Society, Copernicus GmbH
ISSN:1680-7316
COBISS.SI-ID:23215911 New window

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