In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 22, No. 11 ( 2022-06-15), p. 7713-7726
Abstract:
Abstract. Secondary organic aerosols (SOAs) account for a large fraction of atmospheric
aerosol mass and play significant roles in visibility impairment by
scattering solar radiation. However, comprehensive evaluations of SOA
scattering abilities under ambient relative humidity (RH) conditions on the
basis of field measurements are still lacking due to the difficulty of
simultaneously direct quantifications of SOA scattering efficiency in dry
state and SOA water uptake abilities. In this study, field measurements of
aerosol chemical and physical properties were conducted in winter in Guangzhou
(lasting about 3 months) using a humidified nephelometer system and
aerosol chemical speciation monitor. A modified multilinear regression model
was proposed to retrieve dry-state mass scattering efficiencies (MSEs,
defined as scattering coefficient per unit aerosol mass) of aerosol
components. The more oxidized oxygenated organic aerosol (MOOA) with an O/C
ratio of 1.17 was identified as the most efficient light scattering aerosol
component. On average, 34 % mass contribution of MOOA to total submicron
organic aerosol mass contributed 51 % of dry-state organic aerosol
scattering. The overall organic aerosol hygroscopicity parameter κOA
was quantified directly through hygroscopicity closure, and hygroscopicity
parameters of SOA components were further retrieved using a multilinear
regression model by assuming hydrophobic properties of primary organic
aerosols. The highest water uptake ability of MOOA among organic aerosol
factors was revealed with κMOOA reaching 0.23, thus further
enhancing the fractional contribution of MOOA in ambient organic aerosol
scattering. In particular, the scattering abilities of MOOA were found to be even
higher than those of ammonium nitrate under RH of 〈70 %, which was
identified as the most efficient inorganic scattering aerosol component,
demonstrating that MOOA had the strongest scattering abilities in ambient
air (average RH of 57 %) during winter in Guangzhou. During the observation
period, secondary aerosols contributed dominantly to visibility degradation
(∼70 %), with substantial contributions from MOOA (16 % on
average), demonstrating significant impacts of MOOA on visibility
degradation. The findings of this study demonstrate that more attention needs
to be paid to SOA property changes in future visibility improvement
investigations. Also, more comprehensive studies on MOOA physical properties
and chemical formation are needed to better parameterize its radiative
effects in models and implement targeted control strategies on MOOA
precursors for visibility improvement.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-22-7713-2022
DOI:
10.5194/acp-22-7713-2022-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2022
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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