Organic aerosol in the summertime southeastern United States: components and their link to volatility distribution, oxidation state and hygroscopicity
The volatility distribution of the organic aerosol (OA) and its sources during the Southern Oxidant and Aerosol Study (SOAS; Centreville, Alabama) was constrained using measurements from an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a thermodenuder (TD). P...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/5799/2018/acp-18-5799-2018.pdf |
| Summary: | The volatility distribution of the
organic aerosol (OA) and its sources during the Southern Oxidant and Aerosol
Study (SOAS; Centreville, Alabama) was constrained using measurements from an
Aerodyne high-resolution time-of-flight aerosol mass spectrometer
(HR-ToF-AMS) and a thermodenuder (TD). Positive matrix factorization (PMF)
analysis was applied on both the ambient and thermodenuded high-resolution
mass spectra, leading to four factors: more oxidized oxygenated OA (MO-OOA),
less oxidized oxygenated OA (LO-OOA), an isoprene epoxydiol (IEPOX)-related
factor (isoprene-OA) and biomass burning OA (BBOA). BBOA had the highest mass
fraction remaining (MFR) at 100 °C, followed by the isoprene-OA, and
the LO-OOA. Surprisingly the MO-OOA evaporated the most in the TD. The
estimated effective vaporization enthalpies assuming an evaporation
coefficient equal to unity were 58 ± 13 kJ mol<sup>−1</sup> for the LO-OOA,
89 ± 10 kJ mol<sup>−1</sup> for the MO-OOA, 55 ± 11 kJ mol<sup>−1</sup>
for the BBOA, and 63 ± 15 kJ mol<sup>−1</sup> for the isoprene-OA. The
estimated volatility distribution of all factors covered a wide range
including both semi-volatile and low-volatility components. BBOA had the
lowest average volatility of all factors, even though it had the lowest
O : C ratio among all factors. LO-OOA was the more volatile factor and
its high MFR was due to its low enthalpy of vaporization according to the
model. The isoprene-OA factor had intermediate volatility, quite higher than
suggested by a few other studies. The analysis suggests that deducing the
volatility of a factor only from its MFR could lead to erroneous conclusions.
The oxygen content of the factors can be combined with their estimated
volatility and hygroscopicity to provide a better view of their physical
properties. |
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| ISSN: | 1680-7316 1680-7324 |