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 Angstrom exponent (AAE), and scattering Angstrom 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.

中文翻译：

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冷温带森林有机物质的生物排放对气溶胶光学特性的影响

摘要 有机物的陆地生物排放会影响大气气溶胶的光学特性，从而影响辐射收支。为了对此进行研究，将过滤器上收集的亚微米水溶性气溶胶 (WSA) 的化学参数与日本北部凉爽温带森林地区的天空辐射计测量的光学特性进行了比较。2015年6月至2015年12月，WSA样本在森林冠层内采集，而气溶胶光学深度（AOD）、单次散射反照率（SSA）、吸收埃指数（AAE）和散射埃指数（SAE）则在森林冠层上方回测. 只有当气溶胶粒子从森林冠层到其上方空气的垂直传输显着时，才将光学特性与基于过滤器的化学参数进行比较。结果表明, AOD 和 WSA 的质量浓度表现出相似且明显的季节性变化, 并在夏季和秋季达到峰值。在夏季，硫酸盐占 WSA 质量的 60%，这与高 SSA (>0.95)、低 AAE (1.15 ± 0.84) 和低 SAE (1.25 ± 0.22) 相关。相比之下，秋季水溶性有机物（WSOM）占 WSA 质量的 70%。WSOM 的很大一部分与 SSA (0.90–0.95) 的减少以及 AAE (2.45 ± 0.91) 和 SAE (1.46 ± 0.15) 的增加有关。结果表明，在夏季，具有较大粒径范围的气溶胶颗粒对应于以硫酸盐为主的气溶胶化学成分。相比之下，在较短波长处具有强光吸收的较小颗粒可能在秋季很重要，并且与以 WSOM 为主的成分有关。秋季的大部分 WSOM 以前与森林地面 α-蒎烯的排放以及随后的生物二次有机气溶胶 (BSOA) 的形成有关。这项研究表明，α-蒎烯衍生的 SOA，主要来自森林地面，与夏季到秋季 SSA 的减少有关。这个过程可以在区域范围内调节辐射效应。