成都市一次重雾霾期间PM_(10)自组织演化的分形特征及DFA分析

Fractal feature and DFA analysis of PM_(10) evolution in a typical fog-haze episode in Chengdu

运用计盒维数法和消除趋势波动分析方法,研究了成都市2013年1月8—20日一次重度雾霾期间,草堂寺、金牛坝、三道堰和十里店4个监测站点连续PM10小时平均质量浓度序列的时间演化规律。雾霾期间4个监测站点的PM10质量浓度序列在某一临界质量浓度以下均表现出标度不变分形结构和长期持续性非线性特征,且这两种物理特征具有很好的动力学同步性;但一旦超过临界质量浓度,PM10演化的长期持续性特征就会消失,PM10演化的标度不变分形结构也随之消失。进一步根据自组织临界(SOC)理论,探讨了导致此次成都重度雾霾期间PM10污染演化呈现分形结构和长期持续性特征的内在动力学机制,并将雾霾天气大气污染系统的动态特征与自组织临界性的判断标准进行了对比分析。结果表明,大气PM10污染演化具有自组织临界性复杂系统的基本特征,此次成都重度雾霾期间PM10在临界质量浓度以下的波动演化主要受系统自组织内禀动力机制主导控制。在该机制的影响下,即使在雾霾期间,污染源排放相对平稳,城市大气系统也相对稳定,但PM10污染演化仍会出现非线性波动,从而导致极高PM10质量浓度的涌现。这一特征可能是由SOC特有的内禀敏感性和不可预测性决定的,也正是由于SOC系统的稳定性使得此次成都重度雾霾污染持续时间很长。

The present paper aims to report the temporal scaling properties of the hourly PM10 average concentration series in a typical fog-haze episode （from Jan. 8 to Jan. 20, 2013） in Chengdu, Sichuan. Among the eight automatic monitoring stations in the city, we have chosen four for fear to miss the necessary PM10 data in-situ, that is, the stations of Caotangsi, Jinniuba, Sandaoyan and Shilidian. When the samples were made ready, we began to prepare the testing data sets in accordance with the standards set by the China National Environmental Monitoring Centre. The box accounting dimension analysis of the four stations shows that, under a certain critical concentration, the evolutionary situation of PM10 reveals a scaleinvariant feature. Further detrended fluctuation analysis of the four stations indicates that, under the same criteria, the PM10 mass concentration exhibit long-term persistence. The above mentioned two to tally different physical features can be said entailing a nice dynamic coincidence. Thai is to say, if the PM10 content level is over the criti- cal concentration, there will be a disappearance of long-term persis- tence property, as well as the scale-invariant structure. It is for this reason that we would like to explore the regularity or the working principle that may account for the complicated fog-haze situation in the city. What is more, it comes to mind that the aforementioned characteristics can be recognized as the footprint of self-organized criticality （SOC）. Furthermore, based on the SOC theory, we have made an exploration of the inherent dynamic mechanism that may ac- count for the scale-invariant behaviors and long-term persistence of PM10 evolution. A comparative investigation of the dynamic features of air pollution in the fog-haze days and the criteria of SOC shows that PM10 evolution has the basic characteristics of self-organized criticali- ty, revealing that the intrinsic dynamic mechanism of SOC in the foghaze days that should account for the temporal evolution of PM10, which tends to make the dense PMI0 mass hanging over there undisturbed for a long term of a day or even for a couple of days, though we are still not be clear of the intrinsic nature of SOC. Therefore, it is necessary to strengthen the efforts for further research of the dynamic evolutionary process of PM10.