In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 20, No. 4 ( 2020-02-28), p. 2445-2470
Abstract:
Abstract. Black carbon (BC) aerosols have been widely recognized as
a vital climate forcer in the atmosphere. Amplification of light absorption
can occur due to coatings on BC during atmospheric aging, an effect that
remains uncertain in accessing the radiative forcing of BC. Existing studies
on the absorption enhancement factor (Eabs) have poor coverage on both
seasonal and diurnal scales. In this study, we applied a recently developed
minimum R squared (MRS) method, which can cover both seasonal and diurnal
scales, for Eabs quantification. Using field measurement data in
Guangzhou, the aims of this study are to explore (1) the temporal dynamics of
BC optical properties at seasonal (wet season, 31 July–10 September; dry
season, 15 November 2017–15 January 2018) and diel scales (1 h time
resolution) in the typical urban environment and (2) the influencing factors on
Eabs temporal variability. Mass absorption efficiency at 520 nm by
primary aerosols (MAEp520) determined by the MRS method exhibited a strong
seasonality (8.6 m2 g−1 in the wet season and 16.8 m2 g−1
in the dry season). Eabs520 was higher in the wet season (1.51±0.50) and lower in the dry season (1.29±0.28). Absorption
Ångström exponent (AAE470–660) in the dry season (1.46±0.12) was higher than that in the wet season (1.37±0.10). Collective
evidence showed that the active biomass burning (BB) in the dry season
effectively altered the optical properties of BC, leading to elevated MAE,
MAEp and AAE in the dry season compared to those in the wet season.
Diurnal Eabs520 was positively correlated with AAE470–660 (R2=0.71) and negatively correlated with the AE33 aerosol loading
compensation parameter (k) (R2=0.74) in the wet season, but these
correlations were significantly weaker in the dry season, which may be
related to the impact of BB. This result suggests that during the wet
season, the lensing effect was more likely dominating the AAE diurnal
variability rather than the contribution from brown carbon (BrC). Secondary
processing can affect Eabs diurnal dynamics. The Eabs520 exhibited
a clear dependency on the ratio of secondary organic carbon to organic carbon (SOC∕OC), confirming the contribution of secondary organic aerosols to
Eabs; Eabs520 correlated well with nitrate and showed a clear
dependence on temperature. This new finding implies that gas–particle
partitioning of semivolatile compounds may potentially play an important
role in steering the diurnal fluctuation of Eabs520. In the dry season,
the diurnal variability in Eabs520 was associated with photochemical
aging as evidenced by the good correlation (R2=0.69) between oxidant
concentrations (Ox=O3+NO2) and Eabs520.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-20-2445-2020
DOI:
10.5194/acp-20-2445-2020-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2020
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
