Department of Mathematics and Physics, University of Salento, 73100, Lecce, Italy.
SCOLAb, Física Aplicada, Universidad Miguel Hernandez, 03202, Elche, Spain.
Environ Sci Pollut Res Int. 2015 Nov;22(21):16570-89. doi: 10.1007/s11356-015-4850-7. Epub 2015 Jun 17.
Columnar and ground-level aerosol optical properties co-located in space and time and retrieved from sun/sky photometer and nephelometer measurements, respectively, have been analyzed to investigate the impact of local and transboundary pollution, to analyze their relationships, and hence to contribute to the aerosol load characterization over the Central Mediterranean. The aerosol optical depth (AOD) at 440 nm, the Ångström exponent (Å) calculated from the AOD at 440 and 675 nm, and the asymmetry parameter (g col ) at 440 nm represent the investigated columnar aerosol parameters. The scattering coefficient (σ p) at 450 nm, the scattering Ångström exponent (å) calculated from σ p at 450 and 635 nm, and the asymmetry parameter (g) at 450 nm are the corresponding ground-level parameters. It is shown that the columnar and ground-level aerosol properties were significantly and similarly affected by the main airflows identified with backtrajectory cluster analysis. The yearly averaged daily evolution of σ p, å, and g was fairly correlated to the one of the AOD, Å, and g col , respectively. These results indicate that the aerosol particles were on average characterized by similar yearly averaged optical properties up to the ground level. In particular, the yearly means of columnar and ground-level Ångström exponents, 1.3 ± 0.4 and 1.1 ± 0.4, respectively, which are close to one, reveal a coarse-mode aerosol contribution in addition to the fine-mode particle contribution up to the ground level. Hourly means, day-by-day, and seasonal daily patterns of ground-level parameters were, however, very weakly correlated with the corresponding columnar parameters. The large impact of the local meteorology on the daily evolution of the ground-level aerosol properties, which makes the impact of long-range transported particles less apparent, was mainly responsible for these last results. It has also been found that columnar Ångström exponents much smaller than one may not be linked to å values smaller than 1. This may occurs when coarse-mode particle plumes, advected at high altitudes, do not penetrate inside the planetary boundary layer. Ångström exponents smaller than 1 are due to a significant contribution of coarse-mode particles as dust particles. Therefore, it is shown that å represents one of the best parameters to infer the contribution of coarse-mode particles at the ground level. The daily evolution of the aerosol properties referring to working days (Monday to Friday) and Sunday and the weekly cycle have suggested that the aerosol source contributions varied during the weekends. In particular, the AOD was characterized by a negative weekly cycle (higher AOD values during the weekend than during the weekdays), the Sunday σ p daily mean was 11 % larger than the Monday value, and å reached the highest value on Sunday. The impact up to the ground level of the weekdays' transboundary pollution, which reaches the monitoring site during the weekends, has likely contributed to these results.
对分别通过太阳/天空光度计和浊度计测量获得的时空共定位柱状和气溶胶光学特性进行了分析，以研究本地和跨境污染的影响，分析它们之间的关系，从而有助于描述中地中海地区的气溶胶负荷特征。440nm 处的气溶胶光学深度（AOD）、440nm 和 675nm 处的 AOD 计算得到的 Angstrom 指数（Å）以及 440nm 处的不对称参数（gcol）表示所研究的柱状气溶胶参数。450nm 处的散射系数（σp）、450nm 和 635nm 处的 σp 计算得到的散射 Angstrom 指数（å）以及 450nm 处的不对称参数（g）是相应的地面水平参数。结果表明，柱状和气溶胶水平特性均受到主要气流的显著和类似影响，这些气流通过轨迹聚类分析确定。σp、å和 g 的日平均每日变化与 AOD、Å和 gcol 的日平均每日变化相当相关。这些结果表明，气溶胶粒子在平均水平上具有相似的平均年度光学特性。特别是，柱状和气溶胶水平 Ångstrom 指数的年平均值分别为 1.3±0.4 和 1.1±0.4，接近 1，这表明在地面水平上除了细颗粒贡献之外，还存在粗颗粒贡献。然而，地面水平参数的逐时均值、逐日常规模式和季节性日模式与相应的柱状参数相关性很弱。当地气象对地面气溶胶特性日演变的巨大影响，使得长程传输颗粒的影响不那么明显，是造成这些结果的主要原因。还发现，小于 1 的柱状 Ångstrom 指数可能与小于 1 的å值无关。这可能发生在高空输送的粗颗粒羽流未穿透行星边界层的情况下。小于 1 的 Ångstrom 指数是由于尘埃颗粒等粗颗粒的显著贡献。因此，结果表明，å是推断地面水平上粗颗粒贡献的最佳参数之一。与工作日（周一至周五）和周日相关的气溶胶特性的日演变以及每周循环表明，气溶胶源贡献在周末期间有所变化。特别是，AOD 具有负的每周循环（周末的 AOD 值高于工作日），周日的σp 日平均值比周一的值高 11%，å周日达到最高值。周末到达监测站的工作日跨境污染对地面水平的影响可能导致了这些结果。
