Wet and dry deposition of mineral dust particles in Japan: factors related to temporal variation and spatial distribution
Wet and dry deposition of mineral dust particles in Japan: factors related to temporal variation and spatial distribution
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DOI：
10.5194/acp-14-1107-2014
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发表时间：
2013-08
影响因子：
6.3
通讯作者：
K. Osada;S. Ura;M. Kagawa;Masaaki Mikami;T. Tanaka;S. Matoba;Kazuma Aoki;M. Shinoda;Y. Kurosaki-Y
中科院分区：
文献类型：
--
作者：
K. Osada;S. Ura;M. Kagawa;Masaaki Mikami;T. Tanaka;S. Matoba;Kazuma Aoki;M. Shinoda;Y. Kurosaki-Y
抽象。最近的地面网络和卫星遥感观测提供了有关大气中矿物尘埃颗粒的空间和垂直分布的有用数据。然而，矿物粉尘沉降通量的时间变化和空间分布的测量是有限的，在其持续时间，位置和过程的沉积。为了确定干湿过程中矿物粉尘沉积的时间变化和空间分布，2008年10月至2010年12月期间，使用自动干湿分离采样器在日本的札幌、富山、名古屋、鸟取、福冈和鹤都角（冲绳）采集了每周沉积样本。矿物粉尘的重量在水不溶性残留物中估计铁含量测量使用X射线荧光分析仪。矿物粉尘的干湿沉降通量春季高，夏季低，表现出类似的季节变化的风成尘事件（Kosa）在日本的频率。在湿沉降方面，2009年和2010年的平均值是富山（9.6 g m −2 yr −1）和海多角（1.7 g m −2 yr −1）的年粉尘通量最高和最低。在富山和鸟取观测到较高的湿沉降通量，在沙尘季节观测到频繁的降水（>每月60%的天数）。在富山、鸟取、福冈和鹤都角的干沉降中，2009年和2010年的平均值分别为福冈（5.2 g m −2 yr −1）和鹤都角（2.0 g m −2 yr −1）。干湿沉降通量的平均比值在富山最高（3.3），在Hedo最低（0.82），表明西部站点的干过程贡献较大，这可能是由于远离沙漠源区以及在沙尘季节湿过程的有效性。耐火粉尘颗粒的粒度分布是通过四级过滤获得的：> 20、> 10、> 5和> 1 μm直径。在大多数事件样品中，大于20 μm和10-20 μm（巨组分）之和的重量分数大于50%。无论沉积类型如何，巨尘分数一般随着距离源区的距离增加而减少，这表明在大气传输过程中较大的巨粒子的选择性耗尽。根据PMc（2.5Dc.在较强的位温层结（5 K km −1）下，观测到了具有高PM c浓度的低干尘埃沉积，其中较薄和较低（c）的尘埃颗粒只有在到达日本时由于快速重力沉降而耗尽巨大尘埃颗粒后才幸存下来。相反，通过较厚（> 2公里）的尘埃层，弱的垂直梯度的位温携带更多的巨型尘埃粒子到日本。由于巨尘颗粒是尘埃积累的重要质量分数，特别是在北太平洋，这是一个高营养，低叶绿素（HNLC）地区，巨尘颗粒的传输高度和分数是研究大气中的尘埃收支及其在地球化学循环中的作用的重要因素。
Abstract. Recent ground networks and satellite remote-sensing observations have provided useful data related to spatial and vertical distributions of mineral dust particles in the atmosphere. However, measurements of temporal variations and spatial distributions of mineral dust deposition fluxes are limited in terms of their duration, location, and processes of deposition. To ascertain temporal variations and spatial distributions of mineral dust deposition using wet and dry processes, weekly deposition samples were obtained at Sapporo, Toyama, Nagoya, Tottori, Fukuoka, and Cape Hedo (Okinawa) in Japan during October 2008–December 2010 using automatic wet and dry separating samplers. Mineral dust weights in water-insoluble residue were estimated from Fe contents measured using an X-ray fluorescence analyser. Wet and dry deposition fluxes of mineral dusts were both high in spring and low in summer, showing similar seasonal variations to frequency of aeolian dust events (Kosa) in Japan. For wet deposition, highest and lowest annual dust fluxes were found at Toyama (9.6 g m −2 yr −1 ) and at Cape Hedo (1.7 g m −2 yr −1 ) as average values in 2009 and 2010. Higher wet deposition fluxes were observed at Toyama and Tottori, where frequent precipitation (> 60% days per month) was observed during dusty seasons. For dry deposition among Toyama, Tottori, Fukuoka, and Cape Hedo, the highest and lowest annual dust fluxes were found respectively at Fukuoka (5.2 g m −2 yr −1 ) and at Cape Hedo (2.0 g m −2 yr −1 ) as average values in 2009 and 2010. The average ratio of wet and dry deposition fluxes was the highest at Toyama (3.3) and the lowest at Hedo (0.82), showing a larger contribution of the dry process at western sites, probably because of the distance from desert source regions and because of the effectiveness of the wet process in the dusty season. Size distributions of refractory dust particles were obtained using four-stage filtration: > 20, > 10, > 5, and > 1 μm diameter. Weight fractions of the sum of > 20 μm and 10–20 μm (giant fraction) were higher than 50% for most of the event samples. Irrespective of the deposition type, the giant dust fractions generally decreased with increasing distance from the source area, suggesting the selective depletion of larger giant particles during atmospheric transport. Based on temporal variations of PM c (2.5 D c . Low dry dust depositions with high PM c concentrations were observed under stronger (5 K km −1 ) stratification of potential temperature with thinner and lower ( c fraction of dust particles only survived after depletion of giant dust particles by rapid gravitational settling at the time they reach Japan. In contrast, transport through a thicker (> 2 km) dust layer with weak vertical gradient of potential temperature carry more giant dust particles to Japan. Because giant dust particles are an important mass fraction of dust accumulation, especially in the North Pacific, which is known as a high-nutrient, low-chlorophyll (HNLC) region, the transport height and fraction of giant dust particles are important factors for studying dust budgets in the atmosphere and their role in biogeochemical cycles.