[1] [1] Zhang L K, Lu S F, Jiao K L, et al. Pollution characteristics of particulate matter in urban districts of Baotou and their relationships with meteorological conditions[J]. Journal of Atmospheric and Environmental Optics, 2017, 12(6): 401-410.

[2] [2] Yang Y Y, Zhou H, Wang X L, et al. Comparison and analysis of a heavy pollution weather process in the south Changsha-Zhuzhou-Xiangtan and north Beijing-Tianjin-Hebei urban agglomeration[J]. Journal of Catastrophology, 2017, 32(2): 141-145.

[3] [3] Xie Z H, Liu C Q, Shi K. Impacts of PM10 on the radiation environments of the atmosphere in Chengdu City[J]. Research of Environmental Sciences, 2016, 29(7): 972-977.

[4] [4] Shi K. Self-organized criticality of PM2.5 during a typical haze period in Chengdu, China[J]. Acta Scientiae Circumstantiae, 2014, 34(10): 2645-2653.

[5] [5] Parrish D D, Zhu T. Clean air for megacities[J]. Science, 2009, 326(5953): 674-675.

[6] [6] Liu H L, Wu Y, Chen M D, et al. Characteristics of atmospheric PM2.5 in Nanjing City and its cytotoxicity in human lung epithelial cells A549[J]. Research of Environmental Sciences, 2018, 31(10): 1736-1742.

[7] [7] Xie Z X, Qin Y C, Zheng Z C, et al. Assessing the death effect of PM2.5 pollution in cities of atmospheric pollution transmission channel in the Beijing-Tianjin-Hebei district[J]. Acta Scientiae Circumstantiae, 2019, 39(3): 843-852.

[8] [8] Wang Z, Han B, Ni T R, et al. Health risk assessment of trace elements of PM2.5 exposure for the elderly subpopulation in Tianjin, China[J]. Research of Environmental Sciences, 2013, 26(8): 913-918.

[9] [9] Weng Y C, Chang N, Lee T. Nonlinear time series analysis of ground-level ozone dynamics in Southern Taiwan[J]. Journal of Environmental Management, 2008, 87(3): 405-414.

[10] [10] Lu W Z, Wang X K. Evolving trend and self-similarity of ozone pollution in central Hong Kong ambient during 1984-2002[J]. Science of the Total Environment, 2006, 357(1/2/3): 160-168.

[11] [11] Zhu J L, Liu Z G. Long-range persistence of acid deposition[J]. Atmospheric Environment, 2003, 37(19): 2605-2613.

[12] [12] Shi K, Liu C Q, Ai N S. Air quality analysis for Shanghai using multi-fractal approach[J]. Environmental Pollution & Control, 2008, 30(9): 60-64.

[13] [13] Kantelhardt J W, Zschiegner S A, Koscielny-Bunde E, et al. Multifractal detrended fluctuation analysis of nonstationary time series[J]. Physica A: Statistical Mechanics and Its Applications, 2002, 316(1/2/3/4): 87-114.

[14] [14] Schumann A Y, Kantelhardt J W. Multifractal moving average analysis and test of multifractal model with tuned correlations[J]. Physica A: Statistical Mechanics and Its Applications, 2011, 390(14): 2637-2654.

[15] [15] Paladin G, Vulpiani A. Anomalous scaling laws in multifractal objects[J]. Physics Reports, 1987, 156(4): 147-225.

[16] [16] Shen C H, Huang Y, Yan Y N. An analysis of multifractal characteristics of API time series in Nanjing, China[J]. Physica A: Statistical Mechanics and Its Applications, 2016, 451: 171-179.

[17] [17] Huang Y, Liu C Q, Zheng K L, et al. Multifractal analysis of PM2.5 evolution during a typical haze[J]. Environmental Science & Technology, 2019, 42(2): 67-73.

[18] [18] Munoz D A, Galvez C G, Balderas L J A, et al. Multifractal analysis of air pollutants time series[J]. Revista Mexicana De Fisica, 2013, 59(1): 7-13.

[19] [19] Du J, Liu C Q, Huang H L, et al. Multiscale EEMD decomposition of PM2.5 in Chengdu during winter and self-organized criticality of air pollution[J]. Environmental Science & Technology, 2019, 42(8): 133-141.

[20] [20] Wu Z H, Huang N. Ensemble empirical mode decomposition: a noise assisted data analysis method[J]. Advances in Adaptive Data Analysis, 2009, 1(1): 1-41.

[21] [21] Kim T, Shin J Y, Kim S, et al. Identification of relationships between climate indices and long-term precipitation in South Korea using ensemble empirical mode decomposition[J]. Journal of Hydrology, 2018, 557: 726-739.

[22] [22] Wang J, Wang X, Lei X H, et al. Teleconnection analysis of monthly streamflow using ensemble empirical mode decomposition[J]. Journal of Hydrology, 2020, 582: 124411.

[23] [23] Xu M J, Shang P J, Lin A J. Cross-correlation analysis of stock markets using EMD and EEMD[J]. Physica A: Statistical Mechanics and Its Applications, 2016, 442: 82-90.

[24] [24] Zhang N N, Lin A J, Shang P J. Multidimensional k-nearest neighbor model based on EEMD for financial time series forecasting[J]. Physica A: Statistical Mechanics and Its Applications, 2017, 477: 161-173.

[25] [25] Gong X, Lin B Q. Modeling stock market volatility using new HAR-type models[J]. Physica A: Statistical Mechanics and Its Applications, 2019, 516: 194-211.

[26] [26] He T. Study on the Pollution Space Update of Changsha-Zhuzhou-Xiangtan Urban Agglomeration[D]. Changsha: Hunan Normal University, 2016.

[27] [27] He T, Shuai H, Zhu X. Pollution space recognition and pollution distribution of Changsha-Zhuzhou-Xiangtan urban agglomeration[J]. Scientia Geographica Sinica, 2016, 36(7): 1081-1090.

[28] [28] Liao Z H, Fan S J, Huang J, et al. Characteristic analysis of a multi-day pollution event in Chang-Zhu-tan metropolitan area during October 2013[J]. Environmental Science, 2014, 35(11): 4061-4069.

[29] [29] Huang N E, Shen Z, Long S R, et al. The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis[J]. Proceedings: Mathematical, Physical and Engineering Sciences, 1998, 454(1971): 903-995.

[30] [30] Qi O Y, Lu W X, Xin X, et al. Monthly rainfall forecasting using EEMD-SVR based on phase-space reconstruction[J]. Water Resources Management, 2016, 30(7): 2311-2325.

[31] [31] Smitha B, Paul Joseph K. Fractal and multifractal analysis of atherosclerotic plaque in ultrasound images of the carotid artery[J]. Chaos, Solitons & Fractals, 2019, 123: 91-100.

[32] [32] Lahmiri S, Bekiros S. Chaos, randomness and multi-fractality in bitcoin market[J]. Chaos Solitons & Fractals, 2018, 106: 28-34.

[33] [33] Menceur M, Mabrouk A B. A joint multifractal analysis of vector valued non Gibbs measures[J]. Chaos, Solitons & Fractals, 2019, 126: 203-217.

[34] [34] Lahmiri S, Bekiros S, Salvi A. Long-range memory, distributional variation and randomness of bitcoin volatility[J]. Chaos, Solitons & Fractals, 2018, 107: 43-48.

[35] [35] Kantelhardt J W, Rybski D, Zschiegner S A, et al. Multifractality of river runoff and precipitation: Comparison of fluctuation analysis and wavelet methods[J]. Physica A: Statistical Mechanics and Its Applications, 2003, 330(1/2): 240-245.

[36] [36] Shi K, Li W Y, Liu C Q, et al. Multifractal fluctuations of Jiuzhaigou tourists before and after Wenchuan earthquake[J]. Fractals, 2013, 21(1): 1350001.

[37] [37] He J J, Gong S L, Yu Y, et al. Air pollution characteristics and their relation to meteorological conditions during 2014-2015 in major Chinese cities[J]. Environmental Pollution, 2017, 223: 484-496.

[38] [38] Liu T, Gong S L, Yu M, et al. Contributions of meteorology and emission to the 2015 winter severe haze pollution episodes in Northern China[J]. Atmospheric Chemistry and Physics, 2016: 1-17.

[39] [39] Laa I, del Ser J, Padró A, et al. The role of local urban traffic and meteorological conditions in air pollution: A data-based case study in Madrid, Spain[J]. Atmospheric Environment, 2016, 145: 424-438.

[40] [40] Wang Y Q, Zhang X Y, Sun J Y, et al. Spatial and temporal variations of the concentrations of PM10, PM2.5 and PM1 in China[J]. Atmospheric Chemistry and Physics, 2015, 15: 13585-13598.

[41] [41] Liu C Q, Geng H, Shen P, et al. Coupling detrended fluctuation analysis of the relationship between O3 and its precursors-a case study in Taiwan[J]. Atmospheric Environment, 2018, 188: 18-24.