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Long term measurements of aerosol optical properties at a primary forest site in Amazonia

机译：长期测量亚马逊地区主要森林地点的气溶胶光学特性

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pstrongAbstract./strong A long term experiment was conducted in a primary forest area in Amazonia, with continuous in-situ measurements of aerosol optical properties between February 2008 and April 2011, comprising, to our knowledge, the longest database ever in the Amazon Basin. Two major classes of aerosol particles, with significantly different optical properties were identified coarse mode predominant biogenic aerosols in the wet season (Januarya??June), naturally released by the forest metabolism, and fine mode dominated biomass burning aerosols in the dry season (Julya??December), transported from regional fires. Dry particle median scattering coefficients at the wavelength of 550 nm increased from 6.3 Mmsupa??1/sup to 22 Mmsupa??1/sup, whereas absorption at 637 nm increased from 0.5 Mmsupa??1/sup to 2.8 Mmsupa??1/sup from wet to dry season. Most of the scattering in the dry season was attributed to the predominance of fine mode (PMsub2/sub) particles (40a??80% of PMsub10/sub mass), while the enhanced absorption coefficients are attributed to the presence of light absorbing aerosols from biomass burning. As both scattering and absorption increased in the dry season, the single scattering albedo (SSA) did not show a significant seasonal variability, in average 0.86 ?± 0.08 at 637 nm for dry aerosols. Measured particle optical properties were used to estimate the aerosol forcing efficiency at the top of the atmosphere. Results indicate that in this primary forest site the radiative balance was dominated by the cloud cover, particularly in the wet season. Due to the high cloud fractions, the aerosol forcing efficiency absolute values were below a??3.5 W msupa??2/sup in 70% of the wet season days and in 46% of the dry season days. Besides the seasonal variation, the influence of out-of-Basin aerosol sources was observed occasionally. Periods of influence of the Manaus urban plume were detected, characterized by a consistent increase on particle scattering (factor 2.5) and absorption coefficients (factor 5). Episodes of biomass burning and mineral dust particles advected from Africa were observed between January and April, characterized by enhanced concentrations of crustal elements (Al, Si, Ti, Fe) and potassium in the fine mode. During these episodes, median particle absorption coefficients increased by a factor of 2, whereas median SSA values decreased by 7%, in comparison to wet season conditions./p.
机译：> >摘要。我们在亚马逊地区的原始森林地区进行了一项长期实验，在2008年2月至2011年4月之间连续进行了气溶胶光学特性的原位测量，据我们所知，亚马逊盆地中最长的数据库。在湿季（Januarya-6月）中，识别出两种主要类型的气溶胶颗粒，其光学特性差异很大，主要为生物模式的气溶胶，它们是由森林新陈代谢自然释放的，而在干季（Julya）则以精细模式为主的生物质燃烧气溶胶。十二月），从大火中运来。 550 nm处的干粒子中值散射系数从6.3 Mm a ?? 1 增加到22 Mm a ?? 1 ，而637 nm处的吸收从0.5 Mm增加 a ?? 1 至干季的2.8 Mm a ?? 1 。干旱季节的大部分散射归因于细模态（PM 2 ）颗粒（PM 10 质量的40a？80％）的占主导地位，而增强型颗粒则占主导地位。吸收系数归因于来自生物质燃烧的光吸收气溶胶的存在。由于在干燥季节散射和吸收都增加，所以单一散射反照率（SSA）并未显示出明显的季节性变化，干燥气溶胶在637 nm处平均为0.86±0.08。所测量的颗粒光学性质用于估算大气顶部的气溶胶强迫效率。结果表明，在这个原始森林中，辐射平衡主要由云层覆盖，特别是在雨季。由于云量较高，因此在70％的湿季日和46％的旱季日，气溶胶强迫效率绝对值均低于a ?? 3.5 W m a ?? 2 。除季节变化外，偶尔观察到流域外气溶胶源的影响。检测到了马瑙斯市区羽流的影响时期，其特征在于颗粒散射（因子2.5）和吸收系数（因子5）持续增加。在1月至4月之间观察到了非洲吹袭的生物质燃烧和矿物粉尘颗粒的事件，其特征是精细模式中地壳元素（Al，Si，Ti，Fe）和钾的浓度增加。在这些事件中，与雨季相比，中值粒子吸收系数增加了2倍，而SSA中值下降了7％。

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