Optical properties and aging of light-absorbing secondary organic aerosol
The light-absorbing organic aerosol (OA) commonly referred to as “brown carbon” (BrC) has attracted considerable attention in recent years because of its potential to affect atmospheric radiation balance, especially in the ultraviolet region and thus impact photochemical processes. A growing amoun...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/12815/2016/acp-16-12815-2016.pdf |
| Summary: | The light-absorbing organic aerosol (OA) commonly referred to as “brown carbon” (BrC) has attracted considerable attention in recent years because
of its potential to affect atmospheric radiation balance, especially in the
ultraviolet region and thus impact photochemical processes. A growing amount
of data has indicated that BrC is prevalent in the atmosphere, which has
motivated numerous laboratory and field studies; however, our understanding
of the relationship between the chemical composition and optical properties
of BrC remains limited. We conducted chamber experiments to investigate the
effect of various volatile organic carbon (VOC) precursors, NO<sub><i>x</i></sub> concentrations, photolysis
time,
and relative humidity (RH) on the light absorption of selected secondary organic aerosols (SOA). Light absorption of chamber-generated SOA samples,
especially aromatic SOA, was found to increase with NO<sub><i>x</i></sub> concentration,
at moderate RH, and for the shortest photolysis aging times. The highest mass absorption coefficient (MAC) value is observed from toluene SOA products
formed under high-NO<sub><i>x</i></sub> conditions at moderate RH, in which
nitro-aromatics were previously identified as the major light-absorbing
compounds. BrC light absorption is observed to decrease with photolysis time,
correlated with a decline of the organic nitrate fraction of SOA. SOA formed
from mixtures of aromatics and isoprene absorb less visible (Vis) and ultraviolet (UV) light than
SOA formed from aromatic precursors alone on a mass basis. However, the
mixed SOA absorption was underestimated when optical properties were
predicted using a two-product SOA formation model, as done in many current
climate models. Further investigation, including analysis on detailed
mechanisms, are required to explain the discrepancy. |
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| ISSN: | 1680-7316 1680-7324 |