Using Morlet wavelet analysis to analyze multiple time scale periodically in PM2.5 in Beijing
LI Zi-ming1,2, SUN Zhao-bin1,2, SHAO Xie3, LIAO Xiao-nong2, ZHANG Xiao-ling2, XIONG Ya-jun2, MA Xiao-hui2
1. Institute of Urban Meteorology, China Meteorological Administration, Beijing 100089, China; 2. Environmental Meteorology Forecast Center of Beijing-Tianjin-Hebei, Beijing 100089, China; 3. National Climate Center, Beijing 100081, China
Abstract：The variation period of PM2.5 concentration and its evolution feature in Beijing urban area were investigated using the Morlet wavelet analysis and Cross wavelet transform (XWT) method. Theobservation data of PM2.5 concentration and meteorological elements from 2010 to 2015 were applied in this study. The results showed that there were significant periodic variations in PM2.5 in Beijing urban, with major period of 24h, 8d and 14d. The 14d period was mainly influenced by quasi-two-week atmosphericoscillation. The 8d period was not only related to the synoptic scale of weather system, but also related to the "weekend effect" caused by human activities, in which the synoptic scale system was probably playing the leading role. There were obvious sympathetic vibrationsin PM2.5 and average wind speed in the frequency period of 8d and 14d, and the anti-phase relationbetween them was also found. Diurnal variations of meteorological condition and anthropogenic emissions might be important factors causing the oscillation period of 24h. These oscillation periods were strongly significant in autumn and winter, because the flow patterns of lower atmosphere was more frequently influenced by strong synoptic systems. Weak oscillation in spring and summer was mainly attributedto low concentration level of PM2.5, multiple influencing factors and intensivemeso-scale thermal circulation induced by topography. The emission reduction measuresmight bethe important factor in weakening Madden-Julian Oscillation after 2014. Although this study achieved some conclusions about oscillation period of PM2.5 in Beijing urban and its evolution feature more measured data and other analytic methods should be verify in future.
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