Spatial characterization of periodic behaviors of ground PM2.5 concentration across the Yangtze River Delta and the North China Plain during 2014–2024: A new insight on driving processes of regional air pollution

Fine particulate matter (PM_2.5) has long been the major air pollutant across China, but its periodic behaviors are still not comprehensively understood at a regional scale. Spatial characterization of the periodic behaviors can sufficiently extract the spatiotemporal information of PM_2.5 time series and provide additional insights to understand key drivers of regional air pollution. This study collected PM_2.5 hourly concentrations at 168 sites across the Yangtze River Delta (YRD) and the North China Plain (NCP) during 2014-2024 and identified PM_2.5 periodic behaviors based on a fast Fourier transform (FFT) algorithm with a pseudo F statistic extraction and harmonic regression analysis with a linear trend term. Spatial characterization of PM_2.5 concentration periodicity was explored in long-term trend, daily and annual cycles. Results showed more local emissions and atmospheric upward dissipation in the NCP resulted in a stronger daily vibration of PM_2.5 concentration rather than in the YRD. Greater annual amplitude in the NCP than in the YRD reflected the significantly-elevated emissions from coal combustion for domestic heat in cold season. A strongly negative correlation between annual amplitude of PM_2.5 concentrations and spatial latitude of monitoring sites across the NCP was attributed to the decreasing washing-out effect of precipitation from southeast to northwest. PM_2.5 concentration across both regions was experienced a long-term decreasing trend in 2014-2024 and the trend has slowed down after 2021. This study provided a new insight on driving PM_2.5 concentrations across the NCP and the YRD of China and underlined the importance of periodic behaviors as complementing PM_2.5 characterization.