Vertical profiles of black carbon measured by a micro-aethalometer in summerin the North China Plain
Vertical profiles of black carbon measured by a micro-aethalometer in summerin the North China Plain
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DOI：
10.5194/acp-16-10441-2016
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发表时间：
2016-08
影响因子：
6.3
通讯作者：
L. Ran;Z. Deng;Xiaobin Xu;P. Yan;Weili Lin;Ying Wang;P. Tian;Pucai C. Wang;W. Pan;D. Lu
中科院分区：
文献类型：
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作者：
L. Ran;Z. Deng;Xiaobin Xu;P. Yan;Weili Lin;Ying Wang;P. Tian;Pucai C. Wang;W. Pan;D. Lu
抽象的。黑碳 (BC) 是可见光谱中的主要吸收剂，也是气候影响的一个重要因素。 2014 年夏季，在痕量气体和气溶胶垂直观测 (VOGA) 野外活动期间，在华北平原 (NCP) 的一个半农村地区，使用连接在系留气球上的微型高度计测量了黑碳的垂直剖面。首次在NCP地区研究了混合层（ML）演变后BC垂直分布的日循环。针对 67 个垂直剖面的选定数据集获得了统计参数，包括确定的混合高度 (Hm) 以及 ML 内 (Cm) 和自由对流层 (Cf) 中的平均 BC 质量浓度。 Hm通常在清晨低于0.2公里，此后因湍流加强而迅速上升。 ML 的最大高度在下午晚些时候达到。夏季晴天时，完全发育的 ML 顶部超过 1 公里，而阴天时则保持较低。日落引发了ML的塌陷，并逐渐形成了稳定的夜间边界层（NBL）。因此，Cm 水平最高出现在清晨，最低水平出现在下午。白天，BC在ML内几乎均匀分布，在ML以上显着下降。现场监测期间，Cm平均约为5.16 ± 2.49 µg m−3，范围为1.12至14.49 µg m−3，与意大利米兰和中国上海等许多污染城市地区的观测结果相当。随着傍晚的临近，BC 逐渐在地表附近堆积，并随着高度呈指数下降。与 Hm 和 Cm 中发现的巨大变化相反，Cf 在一天中相对不受影响。在清洁条件下，Cf 不到地面水平的 10%，而在某些污染情况下，Cf 达到地面水平的一半。 BC垂直剖面的原位测量有望对准确估计BC的直接辐射强迫和改善该地区气溶胶光学特性的遥感反演具有重要意义。
Abstract. Black carbon (BC) is a dominant absorber in the visible spectrum and a potent factor in climatic effects. Vertical profiles of BC were measured using a micro-aethalometer attached to a tethered balloon during the Vertical Observations of trace Gases and Aerosols (VOGA) field campaign, in summer 2014 at a semirural site in the North China Plain (NCP). The diurnal cycle of BC vertical distributions following the evolution of the mixing layer (ML) was investigated for the first time in the NCP region. Statistical parameters including identified mixing height (Hm) and average BC mass concentrations within the ML (Cm) and in the free troposphere (Cf) were obtained for a selected dataset of 67 vertical profiles. Hm was usually lower than 0.2 km in the early morning and rapidly rose thereafter due to strengthened turbulence. The maximum height of the ML was reached in the late afternoon. The top of a full developed ML exceeded 1 km on sunny days in summer, while it stayed much lower on cloudy days. The sunset triggered the collapse of the ML, and a stable nocturnal boundary layer (NBL) gradually formed. Accordingly, the highest level Cm was found in the early morning and the lowest was found in the afternoon. In the daytime, BC was almost uniformly distributed within the ML and significantly decreased above the ML. During the field campaign, Cm averaged about 5.16 ± 2.49 µg m−3, with a range of 1.12 to 14.49 µg m−3, comparable with observational results in many polluted urban areas such as Milan in Italy and Shanghai in China. As evening approached, BC gradually built up near the surface and exponentially declined with height. In contrast to the large variability found both in Hm and Cm, Cf stayed relatively unaffected through the day. Cf was less than 10 % of the ground level under clean conditions, while it amounted to half of the ground level in some polluted cases. In situ measurements of BC vertical profiles would hopefully have an important implication for accurately estimating direct radiative forcing by BC and improving the retrieval of aerosol optical properties by remote sensing in this region.