Brown carbon (BrC) plays an important role in global radiative budget but there have been few studies on BrC in Arctic despite rapid warming and increasing wildfires in this region. Here we investigate the optical properties of BrC from boreal fires in Alaska summer, with two sets of measurements from PILS-LWCC-TOC (Particle-Into-Liquid-Sampler – Liquid-Waveguide Capillary flow-through optical Cell - Total-Organic-Carbon analyzer) and filter measurements. We show that during intense wildfires, the mass absorption coefficient at 365 nm (MAC) from water soluble organic carbon (WSOC) remained stable at ∼1 m g. With all plumes sampled and derived transport time, we show a decrease of MAC with plume age, with a shorter photobleaching lifetime (∼11 h) at 365 nm compared to 405 nm (∼20 h). The total absorption by organic aerosols measured from filters at 365 nm is higher than the absorption by WSOC by a factor 2–3, suggesting a dominant role of insoluble organic carbon. Overall BrC dominates absorption in the near-ultraviolet and visible radiation during wildfire season in Alaska summer.

中文翻译：

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阿拉斯加夏季北方森林火灾中棕色碳及其光学特性的测量

棕碳（BrC）在全球辐射预算中发挥着重要作用，但尽管该地区气候迅速变暖且野火不断增加，但对北极 BrC 的研究却很少。在这里，我们通过 PILS-LWCC-TOC（颗粒进入液体采样器 - 液体波导毛细管流通光学池 - 总有机碳）进行两组测量，研究了阿拉斯加夏季北方火灾中 BrC 的光学特性分析仪）和滤波器测量。我们发现，在强烈的野火期间，水溶性有机碳（WSOC）在 365 nm 处的质量吸收系数（MAC）保持稳定在~1 m g。通过对所有羽流采样和导出的传输时间，我们发现 MAC 随着羽流年龄的增加而降低，与 405 nm（～20 小时）相比，365 nm 处的光漂白寿命（～11 小时）更短。从过滤器在 365 nm 处测得的有机气溶胶的总吸收比 WSOC 的吸收高 2-3 倍，表明不溶性有机碳占主导地位。在阿拉斯加夏季野火季节期间，总体而言，BrC 在近紫外和可见辐射的吸收中占主导地位。