An extremely low visibility event over the Guangzhou region: A case study
An extremely low visibility event over the Guangzhou region: A case study
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DOI：
10.1016/j.atmosenv.2005.07.061
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发表时间：
2005-11-01
影响因子：
5
通讯作者：
Bi, XY
中科院分区：
文献类型：
--
作者：
Wu, D;Tie, XX;Bi, XY
在中国南方的广州地区，也被称为珠江三角洲（PRD），经常有高浓度的气溶胶。卫星（MODIS）资料显示，该区域的气溶胶光学深度通常大于0.6，被称为亚洲褐云区。在一些极端事件中，这些高气溶胶水平造成了非常低的能见度。在本文中，我们将展示2003年11月2日，日平均能见度小于2 km（瞬时值小于200 m），气溶胶光学深度大于1.2。我们分析这一特殊事件的原因。分析表明，该事件与飓风“Melor 0319”有关。2003年11月2日，飓风位于菲律宾西北部，广州地区不在飓风范围内。飓风在广州地区产生了较强的对流层低层下降运动、较弱的地面风速和较低的行星边界层（PBL）。因此，强烈的下沉引起的下降气流迫使气溶胶颗粒进入很浅的一层，而弱的水平风使气溶胶颗粒保持在源区内，造成了2003年11月2日广州地区气溶胶浓度很高，能见度极低。这一案例分析将有助于更好地了解广州空气质量差的原因，这是未来最终改善空气质量的第一步。例如，当天气条件预计会导致本文所讨论的现象再次发生时，人们可以减少排放。(c) 2005 Elsevier Ltd版权所有。
Over the Guangzhou region, also called the Pearl River Delta (PRD) of Southern China, there are often high aerosol concentrations. The satellite (MODIS) data show that the aerosol optical depth is often higher than 0.6 in this area, which is known as Asian Brown Cloud region. In some extreme events, these high aerosol levels have caused very low visibilities. In this paper, we will show that on 2 November 2003, the daily average visibility is less than 2 km (the instantaneous value is less than 200 m), and the aerosol optical depth is greater than 1.2. We analyze the cause of this particular event. The analysis indicates that this event is related to the hurricane of "Melor 0319". The hurricane is located at the northwest Philippines on 2 November 2003, and the Guangzhou region is outside the hurricane. The hurricane produces a strong descent motion in the lower troposphere, a weak surface wind speed, and a relatively low planetary boundary layer (PBL) in the Guangzhou region. As a result, the strong subsidence causes descending air motions to force the aerosol particles into a very shallow layer, and the weak horizontal wind acts to keep the aerosol particles inside the source region, producing very high aerosol concentrations and extremely low visibility in the Guangzhou region on 2 November 2003. This case analysis will be useful to better understand the causes of the poor air quality over Guangzhou, which is a first step for ultimately improving it in the future. For example, one can reduce emissions when synoptic conditions are expected to cause recurrences of the phenomenon discussed in the paper. (c) 2005 Elsevier Ltd. All rights reserved.