[Spatial Distribution Characteristics of PM 2.5 and O 3 in Beijing-Tianjin-Hebei Region Based on Time Series Decomposition].

Notably, clear spatial differences occur in the distribution of air pollution among cities in the Beijing-Tianjin-Hebei (BTH) Region. Clarifying the concentration distribution of PM _2.5 and O ₃ at different time scales is helpful to formulate scientific and effective pollution prevention and control measures. Here, the concentrations of PM _2.5 and O ₃ were decomposed using a seasonal-trend decomposition procedure based on the loess (STL) method; their long-term, seasonal, and short-term components were obtained; and their temporal and spatial distribution characteristics were studied. The results showed that the decrease in PM _2.5 concentration in the BTH Region from 2017 to 2021 was higher than that of O ₃ . There was a positive correlation between PM _2.5 and O ₃ concentrations in spring and summer and a negative correlation in autumn and winter. The short-term component and seasonal component had the greatest contribution to PM _2.5 and O ₃ concentrations, respectively. There were two principal components in the seasonal and short-term components of PM _2.5 and the long-term and short-term components of O ₃ , corresponding to the central and southern part of Hebei Province and the northern part of the BTH Region. Sub-regional distribution of PM _2.5 and O ₃ in the BTH Region at different time scales were found. Compared with that in the original series, the long-term component could better reflect the evolution trend of PM _2.5 and O ₃ concentrations, and the standard deviation (SD) of the seasonal component and short-term component could be used to measure the fluctuation in PM _2.5 and O ₃ concentrations in various cities. The SD of the seasonal and short-term components of the PM _2.5 concentration in every city in front of Taihang Mountain was higher, and the SD of the short-term component of the O ₃ concentration in Tangshan was the highest.