[Temporal and Spatial Characteristics of Troposphere O₃ and Precursors HCHO and NO₂ in East China]

Based on OMI remote sensing satellite data, the temporal and spatial characteristics of tropospheric ozone (O₃), nitrogen dioxide (NO₂), and formaldehyde (HCHO) concentrations in East China from 2005 to 2021 were analyzed, and the backward trajectory (HYSPLIT) model was used to explore their sources. The results showed that ① during the 17 years, the tropospheric O₃ concentration steadily increased, reached the maximum value in 2010, and then showed a fluctuating and undulating state. NO₂ showed an increasing trend from 2005 to 2012 and slowly decreased from 2012 to 2021. The average HCHO concentration showed an increasing trend from 1.15×10¹⁶molec·cm^-2 in 2005 to 1.8×10¹⁶ molec·cm^-2 in 2021. ② In terms of spatial characteristics, the concentrations of the three pollutants generally showed a pattern of high concentration in the north and low concentration in the south, with a high concentration in the north, uncharacteristic concentration in the middle, and low concentration in the south. ③ The sensitivity of O₃ was as follows:η<2.3 in spring, which belonged to the VOCs control area; η<4.2 in summer, showing that most areas were NO-VOCs coordinated control areas and a few areas were VOCs control areas; η<4.2 in autumn, which was primarily controlled by VOCs, with a few of them being NO-VOC synergistic control areas; and η<2.3 in winter, which was a VOCs-controlled area. VOCs were primarily controlled in Shandong Province. ④ Owing to the high concentration of O₃ in Shandong Province from 2005 to 2021, Jinan, the capital city of Shandong Province in 2021, was selected for ozone source analysis. The O₃ concentration increased in Jinan in 2021 owing to two aspects. First, the long-distance air transportation primarily originated from Lianyungang City in Jiangsu Province and Cangzhou City in Hebei Province. Second, the close air mass transport originated from the pollution of cities near Jinan and the economic zones of the Yellow Sea and Bohai Sea, and the aggregation analysis results corresponded with those of the potential source contribution factor algorithm (PSCF) and the weighted trajectory analysis (CWT).