Dynamic light absorption of biomass-burning organic carbon photochemically aged under natural sunlight
Wood-burning aerosol produced under smoldering conditions was photochemically aged with different relative humidity (RH) and NO<sub>x</sub> conditions using a 104 m<sup>3</sup> dual outdoor chamber under natural sunlight. Light absorption of organic carbon (OC) was measured o...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-02-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/14/1517/2014/acp-14-1517-2014.pdf |
| Summary: | Wood-burning aerosol produced under smoldering conditions was photochemically
aged with different relative humidity (RH) and NO<sub>x</sub> conditions using a
104 m<sup>3</sup> dual outdoor chamber under natural sunlight. Light absorption of
organic carbon (OC) was measured over the course of photooxidation using a
UV–visible spectrometer connected to an integrating sphere. At high RH, the
color decayed rapidly. NO<sub>x</sub> slightly prolonged the color of wood
smoke, suggesting that NO<sub>x</sub> promotes the formation of chromophores via
secondary processes. Overall, the mass absorption cross section (integrated
between 280 and 600 nm) of OC increased by 11–54% (except high RH)
in the morning and then gradually decreased by 19–68% in the afternoon.
This dynamic change in light absorption of wood-burning OC can be explained
by two mechanisms: chromophore formation and sunlight bleaching. To
investigate the effect of chemical transformation on light absorption, wood
smoke particles were characterized using various spectrometers. The intensity
of fluorescence, which is mainly related to polycyclic aromatic hydrocarbons
(PAHs), rapidly decreased with time, indicating the potential bleaching of
PAHs. A decline of levoglucosan concentrations evinced the change of primary
organic aerosol with time. The aerosol water content measured by Fourier
transform infrared spectroscopy showed that wood-burning aerosol became less
hygroscopic as photooxidation proceeded. A similar trend in light absorption
changes has been observed in ambient smoke aerosol originating from the 2012
County Line wildfire in Florida. We conclude that the biomass-burning OC
becomes less light absorbing after 8–9 h sunlight exposure compared to
fresh wood-burning OC. |
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| ISSN: | 1680-7316 1680-7324 |