Abstract
AbstractThe aerosol radiative effect can be modulated by the vertical distribution and optical properties of aerosols, particularly when aerosol layers are decoupled. Direct aerosol radiative effects over the northern South China Sea (SCS) were assessed by incorporating an observed data set of aerosol optical properties obtained from the Seven South East Asian Studies (7‐SEAS)/Dongsha Experiment into a radiative transfer model. Aerosol optical properties for a two‐layer structure of aerosol transport were estimated. In the radiative transfer calculations, aerosol variability (i.e., diversity of source region, aerosol type, and vertical distribution) for the complex aerosol environment was also carefully quantified. The column‐integrated aerosol optical depth (AOD) at 500 nm was 0.1–0.3 for near‐surface aerosols and increased 1–5 times in presence of upper layer biomass‐burning aerosols. A case study showed the strong aerosol absorption (single‐scattering albedo (ω) ≈ 0.92 at 440 nm wavelength) exhibited by the upper layer when associated with predominantly biomass‐burning aerosols, and the ω (≈0.95) of near‐surface aerosols was greater than that of the upper layer aerosols because of the presence of mixed type aerosols. The presence of upper level aerosol transport could enhance the radiative efficiency at the surface (i.e., cooling) and lower atmosphere (i.e., heating) by up to −13.7 and +9.6 W m−2 per AOD, respectively. Such enhancement could potentially modify atmospheric stability, can influence atmospheric circulation, as well as the hydrological cycle over the tropical and low‐latitude marginal northern SCS.
Highlights
Aerosols generated from both natural and anthropogenic sources are distributed through the atmosphere over a wide spatial scale because of air mass transport
The seven-day back trajectories on the measurement days were used for examining the air mass transport paths as they influenced the surface and total columnar aerosol loading measured over Dongsha Island (DSI)
Major back trajectory paths (Figure 1a), indicating the influence of air masses originating from different source regions on the aerosols at the study site, were as follows: 1. Path A: These back trajectories originated from elevated regions over northern China and Mongolia and covered the longest distance through the coastal areas of China; 2
Summary
Aerosols generated from both natural and anthropogenic sources are distributed through the atmosphere over a wide spatial scale because of air mass transport. An accurate understanding of aerosol radiative forcing is crucial for accurately estimating the aerosol climate effect on a regional and global scale [Kedia et al, 2010]. This paper discusses the aerosol optical properties for the near-surface and free-tropospheric layers and their contribution to direct aerosol radiative effects. This study seeks to estimate the aerosol optical properties in the two-layer transport structure by using simultaneously measured AODs, mass concentrations, and chemical composition; these data were obtained from those collected during the 7-SEAS/Dongsha Experiment
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