Quantifying black carbon light absorption enhancement with a novel statistical approach
Black carbon (BC) particles in the atmosphere can absorb more light when coated by non-absorbing or weakly absorbing materials during atmospheric aging, due to the lensing effect. In this study, the light absorption enhancement factor, <i>E</i><sub>abs</sub>, was quantifi...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/289/2018/acp-18-289-2018.pdf |
| Summary: | Black carbon (BC) particles in the atmosphere can absorb more light
when coated by non-absorbing or weakly absorbing materials during
atmospheric aging, due to the lensing effect. In this study, the
light absorption enhancement factor, <i>E</i><sub>abs</sub>, was
quantified using a 1-year measurement of mass absorption
efficiency (MAE) in the Pearl River Delta region (PRD). A new
approach for calculating primary MAE (MAE<sub>p</sub>),
the key for <i>E</i><sub>abs</sub> estimation, is demonstrated using the
minimum <i>R</i> squared (MRS) method, exploring the inherent source
independency between BC and its coating materials. A unique feature
of <i>E</i><sub>abs</sub> estimation with the MRS approach is its
insensitivity to systematic biases in elemental carbon (EC) and <i>σ</i><sub>abs</sub>
measurements. The annual average <i>E</i><sub>abs550</sub> is found to be
1.50 ± 0.48 (±1 SD) in the PRD region, exhibiting a clear
seasonal pattern with higher values in summer and lower in
winter. Elevated <i>E</i><sub>abs</sub> in the summertime is likely
associated with aged air masses, predominantly of marine origin, along
with long-range transport of biomass-burning-influenced air masses
from Southeast Asia. Core–shell Mie simulations along with measured
<i>E</i><sub>abs</sub> and absorption Ångström exponent (AAE) constraints
suggest that in the PRD, the coating materials are unlikely to be
dominated by brown carbon and the coating thickness is higher in the
rainy season than in the dry season. |
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| ISSN: | 1680-7316 1680-7324 |