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In recent years, ground-level-ozone（O 3 ） pollution in urban areas in the Bohai Rim has attracted wide attention. Based on the analysis of the spatiotemporal distribution characteristics of O 3 concentration in Dongying, a representative city in the Bohai Rim from 2017 to 2022, the effects of meteorological factors and sea-land breeze circulation on O 3 concentration were evaluated. The results showed that： ① From 2017 to 2022, the annual assessment value of O 3 concentration in Dongying showed a fluctuating upward trend, and the pollution days with O 3 as the primary pollutant increased. O 3 pollution mainly occurred in spring, summer, and autumn, with the most severe O 3 pollution episodes typically occurring in May and June, and the duration of O 3 pollution season tended to be longer. The monthly variation in the daily maximum 8-h average ozone （MDA8 O 3 ） presented a bimodal distribution, with significant increases in the 5th and 25th percentiles, and the spatial distribution was "high in the north and south, low in the middle." In addition, the nocturnal O 3 concentration in recent years in Dongying also showed a significant increase trend. ② Meteorological factors greatly influenced O 3 concentration in Dongying. When the temperature was greater than 30℃, the relative humidity was less than 50%, and the wind direction was south-southwest or east-northeast, a high O 3 value was more likely to occur. Meteorological factors contributed 30% of the MDA8 O 3 variation in Dongying during the study period. In the case of moderate and severe O 3 pollution, the contribution of meteorological factors to the change in MDA8 O 3 could be as high as 40%. ③ To some extent, sea-land breeze contributed to the occurrence of MDA8 O 3 exceeding the secondary standard limit value of the National Ambient Air Quality Standard. In the afternoon, the hourly concentration of O 3 during the sea-land breeze days was approximately 20 μg·m -3 higher than that during the non-sea-land breeze days. On the days of moderate and severe O 3 pollution, the O 3 concentration during the sea-land breeze days from 10：00 to 16：00 was higher than that during non-sea-land breeze days, and the O 3 concentration was also at a high level from 20：00 to 23：00 on sea-land breeze days. In the O 3 pollution season, the sea-land breeze could significantly affect the O 3 level in coastal cities, which could bring significant challenges for O 3 pollution prevention and control in this region. In the future, cities in the Bohai Rim need to further strengthen regional joint prevention and control of O 3 pollution and increase emission reduction efforts of nitrogen oxides and volatile organic compounds. This strategy could effectively lower pollutant concentrations within the land breeze air mass, consequently reducing the impact of the sea breeze air mass on air quality in cities in the Bohai Rim.

Halocarbons are hot topics in atmospheric environment and climate change research. Combining observational data from six field campaigns at the summit of Mount Taishan (36.25°N, 117.10°E, 1534 m above sea level) with backward trajectory and receptor source analyses, this study analyzed the long-term trends and major emission sources of halocarbons in the regional background atmosphere of the North China Plain (NCP) from 2003 to 2018. The results showed that the volume fraction of species eliminated by the Montreal Protocol (MP) showed a significant downward trend; however, the MP-controlled and unregulated species showed an overall upward trend. Meanwhile, the median volume fraction of the MP-controlled and unregulated species at Mount Taishan were significantly higher than the mid-latitude median background values in the northern hemisphere. Mount Taishan air was mainly affected by four types of air masses, of which the air mass originating from NCP accounted for the highest proportion (41%). The major sources of halocarbons were biomass/biofuel burning (38.1%), refrigeration (26.2%), industrial and domestic solvent use (21.7%), solvent use in the electronic industry (8.7%), and leakage of chlorofluorocarbon (CFCs) banks (5.3%). This study fully demonstrates that MP has been effectively implemented in China and provides evidence and recommendations to further reduce and control the volume fraction of halocarbons.

Atmospheric particle number size distributions were measured by a wide-range particle size spectrometer and a scanning mobility particle size spectrometer in the summertime and wintertime in the coastal area of Qingdao (China). The inorganic and organic gaseous precursors and particulate chemical composition were measured to characterize new particle formation (NPF) events by combining meteorological parameters and backward trajectories. In summer, the occurrence frequency of NPF events was 18% lower. However, the atmospheric particle number concentration increased by approximately 1-4 times during the NPF events compared with those without NPF. The apparent formation rates and growth rates were (5.2±4.3) cm -3 ·s -1 and (6.5±2.2) nm·h -1 , respectively, except for a special NPF event on July 20. The correlation analysis results implied that biogenic volatile organic compounds (BVOCs) seemingly favor NPF, and the reverse is true for anthropogenic volatile organic compounds (AVOCs). The occurrence frequency of NPF events of 27% in winter was clearly higher than that in summer. The apparent formation rates and growth rates, i.e., (3.3±3.1) cm -3 ·s -1 and (5.3±3.3) nm·h -1 , decreased, although the decreases were not significant ( P >0.05). The correlation analyses implied that AVOCs favored NPF. However, BVOCs had no correlation with NPF. For the cases in which new particles could grow to CCN sizes (>50 nm), the particle growth characteristics showed significant seasonal differences, i.e., in summer, new particles could grow to CCN sizes via photochemical reactions, whereas in winter, second-stage growth driven by the formation of nitrate aerosols was needed to grow new particles to CCN sizes.