Source reconciliation of atmospheric dust causing visibility impairment in Class I areas of the western United States
Source reconciliation of atmospheric dust causing visibility impairment in Class I areas of the western United States
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DOI：
10.1029/2008jd009923
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发表时间：
2009-01
影响因子：
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通讯作者：
I. Kavouras;V. Etyemezian;D. DuBois;Jin Xu;M. Pitchford
中科院分区：
文献类型：
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作者：
I. Kavouras;V. Etyemezian;D. DuBois;Jin Xu;M. Pitchford
[1]来自机构间受保护视觉环境监测网络的气溶胶数据、气团反向轨迹、土地利用图、土壤特性图、元素组成的诊断比率和多元线性回归被用作半定量分析的一部分。分析的目的是确定当粗质量(CM)和细土壤(FS)的消光总和大于任何其他气溶胶成分，并且重建的气溶胶消光系数是该地点最高的20%(按历年计算)时，导致某一地点能见度低的扬尘事件的类型。对于这些“最严重的沙尘日”，上述工具被用来将低能见度的原因归因于以下类型的事件之一：(1)源自亚洲的沙尘的跨洲输送；(2)来自现场附近来源的风尘事件；(3)来自网站上风的来源的风尘的输送。根据证据的重要性，这三个事件中的一个事件的分配与置信度的高低有关。由于缺乏令人信服的证据，导致最严重的沙尘日归因于“不确定的事件”。在2001-2003年期间最严重的610个粉尘日中，51%与三种事件类型中的一种有关，置信度高，另有30%的事件置信度低。在与某一事件(低置信度或高置信度)有关的496个最差沙尘日中，亚洲沙尘被指定为55天(2001-2002年)，当地产生的风尘为201天，从易受风蚀影响的上风源区输送的沙尘为240天。与美国和墨西哥震源区的风事件相关的事件显示出最高的尘埃浓度。亚洲沙尘事件与较低的沙尘浓度和较大的FS-CM比率有关。亚洲沙尘和北美大陆沙尘在有机质、黑碳和硝酸盐(NO3-−)含量上有一定差异。这项研究中使用的工具都不足以确定与农业、建筑和机动车辆在铺面和未铺设道路上的机动车辆旅行等人为活动有关的机械扬尘事件。一些最严重的沙尘日可能是由这些类型的活动造成的，特别是在亚利桑那州中部和加利福尼亚州北部和南部，这些地区的未确定事件的比例高于美国西部的其他地区。总而言之，这项研究的方法和结果可以帮助改进大规模扬尘模型的性能，并为洞察在美国西部相对偏远地区导致沙尘产生雾霾的事件类型的分布提供帮助。
[1] Aerosol data from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, air mass backward trajectories, land use maps, soil characteristics maps, diagnostic ratios of elemental composition, and multivariate linear regression were utilized as part of a semiquantitative analysis. The purpose of the analysis was to determine the types of dust-causing events that contribute to low visibility at a given site when the sum of extinction from coarse mass (CM) and fine soil (FS) was larger than any other aerosol component and the reconstructed aerosol extinction coefficient was among the 20% highest (calculated on a calendar year basis) for that site. For these “worst dust days,” the above tools were used to ascribe the cause of low visibility to one of the following types of events: (1) transcontinental transport of dust originating from Asia; (2) windblown dust events from sources located nearby the site and; (3) transport of windblown dust from sources upwind of the site. Depending on the weight of evidence, a low or high level of confidence was associated with the assignment of one of these three events. Absence of convincing evidence resulted in ascribing the worst dust day to “undetermined events.” Of the 610 worst dust days over the 2001–2003 period, 51% were associated with one of the three event types with high confidence and an additional 30% were accounted for with low confidence. Of the 496 worst dust days associated with an event (either low or high confidence), Asian dust was the assigned event on 55 days (for 2001–2002), locally generated windblown dust on 201 days, and transport from upwind source areas susceptible to wind erosion on 240 days. Events associated with windblown episodes from source areas in the United States and Mexico exhibited the highest dust concentrations. Asian dust events were associated with lower dust concentrations and a larger FS-to-CM ratio. Some variations between Asian dust and continental North American dust were observed in organic matter (OMC), black carbon (LAC), and nitrate (NO3−) content. None of the tools used in this study was adequate for identifying events associated with mechanically released dust by anthropogenic activities including, agriculture, construction and motor vehicle travel on paved and unpaved roads. Some of the worst dust days may have been caused by these types of activities, especially in central Arizona and northern and Southern California, where the fraction of undetermined events was higher than in other regions within the western United States. All in all, the methods and results of this study can help improve the performance of large-scale dust emission models and provide insight into the distribution of the types of events that cause dust resultant haze in relatively remote areas of the western United States.