Sánchez M L, García M A, Pérez I A, de Torre B
Department of Applied Physics, University of Valladolid, 47005 Valladolid, Spain.
Chemosphere. 2007 Feb;67(2):229-39. doi: 10.1016/j.chemosphere.2006.10.058. Epub 2007 Jan 4.
This paper presents the hourly evolution of a severe Saharan dust outbreak, (SDO), affecting Central Spain over July 23-24, 2004 measured with a laser remote sensing device at a location close to the Guadarrama mountain range foothills and its impact on PM10 levels (particles with an aerodynamic diameter below 10 microm) recorded at four contrasting monitoring stations located in the upper and lower Spanish plateau, some 170km apart. During the period of study the Saharan dust layer, (SDL), presented significant hourly variability in height (3600-1500m), depth (1500-700m) and aerosol dust loading (extinction coefficient, EC, 0.22-1.28km(-1)). Overnight layering was generally observed whereas a well mixed layer prevailed in the afternoon. The (SDO) impact on the lower levels took place approximately 12h after the (SDL) was initially observed and triggered by a descending dust enriched, evidencing the important role of subsidence over the presence of dust in lower altitudes. During the event, PM10 levels at all the stations exceeded EU air quality daily mean standards, 50 microgm(-3), on 2-4days. The maximum values ranged from 185 to 245 microgm(-3) depending on the monitoring station. The impact on PM10 spread from 2days in the upper plateau to 3-4 in the lower plateau, in agreement with the geographical location of the monitoring stations with respect to the southwest origin of the intrusion. The impact was even more dramatic on PM10 hourly concentrations, leading to maximum hourly peaks ranging from 322 to 598 microgm(-3) again depending on the monitoring station. Correlations between EC vertical profiles and PM10 hourly concentrations at the monitoring stations showed the great influence of the (SDO) on surface concentrations. The best linear fits corresponded to the extinction coefficients in the lower altitudes (close to the lower range of the device 500-650m), EC2, yielding satisfactory correlation coefficients ranging from 0.68 to 0.71. The low variability of the slope of each individual linear fit, 19.2%, shows the similar impact of (SDO) on the PM10 hourly concentrations recorded in the area under study.
本文介绍了2004年7月23日至24日影响西班牙中部的一次严重撒哈拉沙尘爆发（SDO）的逐小时演变情况，该沙尘爆发是在靠近瓜达拉马山脉山麓的一个地点用激光遥感设备测量的，以及它对位于西班牙高原上下、相距约170公里的四个对比监测站记录的PM10水平（空气动力学直径小于10微米的颗粒物）的影响。在研究期间，撒哈拉沙尘层（SDL）在高度（3600 - 1500米）、深度（1500 - 700米）和气溶胶沙尘负荷（消光系数，EC，0.22 - 1.28千米⁻¹）方面呈现出显著的逐小时变化。夜间通常观察到分层现象，而下午则普遍存在混合良好的气层。SDO对较低层的影响大约在最初观测到SDL并由富含沙尘的下沉引发后12小时发生，这证明了下沉在低海拔沙尘存在方面的重要作用。在事件期间，所有监测站的PM10水平在2 - 4天内都超过了欧盟空气质量日均值标准50微克/立方米。最大值范围从185到245微克/立方米，具体取决于监测站。对PM10的影响从高原上部的2天扩展到高原下部的3 - 4天，这与监测站相对于入侵沙尘西南来源的地理位置一致。对PM10每小时浓度的影响更为显著，导致每小时最大峰值范围再次从322到598微克/立方米，具体取决于监测站。监测站处EC垂直剖面与PM10每小时浓度之间的相关性表明SDO对地表浓度有很大影响。最佳线性拟合对应于较低海拔（接近设备较低范围500 - 650米）的消光系数EC2，产生的满意相关系数范围为0.68至0.71。每个单独线性拟合斜率的低变异性为19.2%，表明SDO对研究区域内记录的PM10每小时浓度有类似影响。
