关中地区PM_2.5污染过程的主要参数特征和EMD统计分析

In order to determine the characteristics of the PM_2.5 pollution process in Guanzhong Area and provide theoretical support for early warning and forecasting system, the peak mass concentration of PM_2.5 and the duration of the pollution process were analyzed by using the data of five cities (Xi'an, Xianyang, Baoji, Weinan and Tongchuan City) in Guanzhong Area from 2014 to 2017. The empirical mode decomposition (EMD) algorithm was used to decompose the sea-level pressure data to explain the statistical results gained from PM_2.5 pollution process. The results revealed that: (1) The distribution and concentration of PM_2.5 in the Guanzhong cities had significant regional correlation and time synchronization characteristics. The daily averaged PM_2.5 concentration of the five cities within four years was closed to each other. The difference was between 2-15 μg/m³. (2) The statistical results of pollution duration showed that the Guanzhong Area had a relatively long pollution process in winter, lasting for 11-15 d, while the pollution process in summer was short, lasting for 7-9 d. The statistical results of the peak PM_2.5 mass concentration during the pollution processes indicated that the frequency of pollution levels in the cities was different, especially at moderate pollution levels (and above). Xianyang City had the highest frequency of 16 times, while Tongchuan City had the lowest frequency of 9 times. (3) After using the EMD algorithm to decompose the pressure data, the variation in the oscillation frequency of the fourth mode (IMF4) was found, which accounted for the significant difference in the duration of pollution processes between different cities in different seasons. In conclusion, the EMD modal decomposition of single-station air pressure can better explain the pollutant concentration characteristics in the Guanzhong Area.