Impact of biogenic emissions of organic matter from a cool-temperate forest on aerosol optical properties. (15th May 2020)

• Record Type: Journal Article
• Authors: Müller, Astrid; Aoki, Kazuma; Tachibana, Eri; Hiura, Tsutom; Miyazaki, Yuzo
• Is Part Of: Atmospheric environment. Volume 229(2020)
• Publication Date: 2020-05-15
• Subjects: Biogenic secondary organic aerosols -- Aerosol optical properties -- Water-soluble aerosols -- Sky radiometer; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2020.117413
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: Terrestrial biogenic emissions of organic matter can affect the optical properties of atmospheric aerosols and thus impact the radiation budget. To investigate this, the chemical parameters of submicrometer water-soluble aerosols (WSA) collected on filters were compared to optical properties measured by a sky radiometer at a cool-temperate forest site in northern Japan. From June to December 2015, the WSA samples were collected within the forest canopy, while aerosol optical depth (AOD), single scattering albedo (SSA), absorption Ångström exponent (AAE), and scattering Ångström exponent (SAE) were retrieved above the canopy. The optical properties were compared with the filter-based chemical parameters only when the vertical transport of aerosol particles from the forest canopy to the air above it was significant. The result showed that the AOD and the mass concentrations of WSA exhibited similar and distinct seasonal variations with peaks in summer and autumn. In summer, sulfate accounted for 60% of the mass of WSA, which was linked to a high SSA (>0.95), low AAE (1.15 ± 0.84), and low SAE (1.25 ± 0.22). In contrast, water-soluble organic matter (WSOM) accounted for 70% of the mass of WSA in autumn. This large fraction of WSOM was associated with a decrease in SSA (0.90–0.95) and an increase in AAE (2.45 ± 0.91) and SAE (1.46 ± 0.15). The results suggest that in summer, aerosol particles with a greater size range corresponded to aerosol chemical compositions dominated by sulfate. In contrast, smaller particles with a strong light absorption at shorter wavelengths, were likely important in autumn and associated with a composition dominated by WSOM. The majority of WSOM in autumn has previously been associated with emissions of α-pinene from the forest floor and the subsequent formation of biogenic secondary organic aerosols (BSOA). This study indicates that α-pinene-derived SOAs, mostly originating from the forest floor, were associated with a summer to autumn decrease in SSA. This process can modulate the radiative effect on a regional scale. Highlights: Chemical components and optical properties of aerosols were compared at a cool-temperate forest. Both of the water-soluble aerosol mass and aerosol optical depth showed peaks in summer and autumn. Decrease in single scattering albedo in autumn was linked to the increased organic aerosol mass. Organic matter from forest floor affect aerosol light-absorbing property on a regional scale.