Li Xing
School of Finance, Shanghai University of Finance and Economics, 200433, Shanghai, China.
Physica A. 2021 Mar 1;565:125551. doi: 10.1016/j.physa.2020.125551. Epub 2020 Nov 23.
Due to the COVID-19 pandemic, human activities are largely restricted in Shanghai, China and it is a valuable experiment to testify the correlation of air quality and human activities. In consideration of the complexity of air pollution, this study aims to compare the multifractal characteristics of air quality index (AQI) time series before and during COVID-19 partial lockdown, and analyze the correlations between multifractal parameters of AQI time series and human activities in Shanghai, China. The hourly AQI series in Shanghai from November 27, 2019 to March 23, 2020 is used for this study. Firstly, using the MF-DFA method, the multifractal characteristics of the AQI series are explored. Secondly, the causes of the multifractality of the AQI series are determined. Finally, the correlations between multifractal parameters of AQI time series and human activities are investigated. The multifractal analysis results reveal that the AQI series during COVID-19 partial lockdown also has multifractal characteristics, and the slightly weaker multifractal characteristics and marginally smaller multifractal degree are obtained in comparison with the pre-lockdown phase. However, the contribution of the effective or intrinsic multifractality before and during COVID-19 partial lockdown are very close. The results via the sliding window procedure indicate that the multifractal parameters ( ) show the similar fluctuations along with the fluctuations of passenger volume in Shanghai Metro. Furthermore, it is found that and and adjusted passenger volume in Shanghai Metro are positively correlated. The possible trend is that the higher adjusted passenger volume is, the larger the value of , becomes, which means the stronger multifractal characteristics and larger multifractal degree of air quality system.
由于新冠疫情，中国上海的人类活动受到极大限制，这是验证空气质量与人类活动相关性的一次宝贵试验。考虑到空气污染的复杂性，本研究旨在比较新冠疫情部分封锁前和封锁期间空气质量指数（AQI）时间序列的多重分形特征，并分析中国上海AQI时间序列的多重分形参数与人类活动之间的相关性。本研究使用了2019年11月27日至2020年3月23日上海的每小时AQI序列。首先，使用MF-DFA方法探索AQI序列的多重分形特征。其次，确定AQI序列多重分形性的成因。最后，研究AQI时间序列的多重分形参数与人类活动之间的相关性。多重分形分析结果表明，新冠疫情部分封锁期间的AQI序列也具有多重分形特征，与封锁前阶段相比，多重分形特征略弱，多重分形程度略小。然而，新冠疫情部分封锁前和期间有效或内在多重分形性的贡献非常接近。通过滑动窗口程序得到的结果表明，多重分形参数（ ）随着上海地铁客流量的波动呈现出相似的波动。此外，发现 、 与上海地铁调整后的客流量呈正相关。可能的趋势是，调整后的客流量越高， 、 的值就越大，这意味着空气质量系统的多重分形特征越强，多重分形程度越大。
