以香港港口2013年3月28日发生的工人罢工事件为契机,利用多重分形理论方法对罢工前和罢工中港口近地面O3、NOx随时间演变的多重分形特征进行分析.首先,运用多重分形消除趋势波动分析方法(MF-DFA)分析O3、NOx自身的多重分形特征,结果表明,港口罢工前和罢工中,O3、NOx浓度演化过程表现出非线性、复杂性的多重分形特征,并且污染物的多重分形特征在罢工中更强.接下来,使用多重分形消除趋势交叉波动分析方法(MF-DCCA),对O3、NOx相关性的多重分形特征进行分析,结果表明,二者的交叉相关性存在具有长期记忆性的多重分形特征.最后,对污染物原始序列进行随机重排处理和相位随机处理,对导致污染物多重分形特征的动力来源进行分析,结果表明,港口罢工前后长程相关性在污染物的演化中占有主导控制地位,厚尾分布效应在罢工中较明显,而且由于污染物多重分形特征的长程相关性的动力来源机制,二次污染物O3的浓度在罢工中下降的趋势并不明显,并在一定时间尺度上存在高浓度的风险.研究结果可为分析港口罢工事件对港口城市大气污染的影响及大气污染物的演化机制提供参考.
Taking the strike in Hong Kong port on March 28,2013 as an exemple,the multifractal characteristics of groundlevel O3,NOx before and during the strike in port were studied by multifractal analysis method. Firstly,the multifractal detrended fluctuation analysis method( MF-DFA) was used to investigate the multifractal characteristics of O3 and NOx ,and results show that O3,NOx concentration evolution exhibits non-linear, complex multifractal characteristics before and during the port strike,and the multifractal characteristics of pollutants during strike is stronger than that before strike.Then, the multifractal detrended cross-correlation analysis( MF-DCCA) was used to analyze the multifractal characteristics of O3 and NOx correlation,and results show cross correlation fractal characteristics with long-term memory. Finally,it was conducted for pollutants original sequence random rearrangement process and random phase processing,the power sources resulting in contamination of multiple fractal characteristics were analyzed,and results show that long-range correlations before and during the port strike dominate the evolution of pollutants,and the effect of fat tails is more obvious during the strike. Because of power source mechanism of contaminants multifractal characteristics with long-range correlation,the decreasing trend of secondary pollutants O3 concentration is not obvious during the strike,and which exists high concentration risk in a certain period of time. The study results can provide valuable information for analyzing the effects of port strike on the air pollution and the evolution mechanism of air pollutants in port cities.