In order to investigate the causes of complex air pollution in coastal cities in the Bohai Rim of China, a one-month intensive field observation combined with model simulation was carried out in a typical city named Dongying in September 2022. The results showed that two PM_2.5 and O₃ complex pollution episodes occurred in Dongying in the observation period, with the primary pollutant being O₃. Atmospheric photochemical reactions occurring under unfavorable meteorological conditions led to the production of O₃ while at the same time facilitating the generation of nitrate, sulfate, and other secondary components of PM_2.5 by enhancing the atmospheric oxidizing capacity, which promoted the formation of complex air pollution. It was worth noting that in the context of high pollutants emission, the occurrence of complex air pollution was more sensitive to the variation in meteorological conditions than to the change in pollutants emission. To continuously improve air quality and protect human health in Dongying, it is recommended that an effective regional joint air pollution prevention and control mechanism with neighboring cities should be established in the premise of effective local pollutants reduction, and special attention should be paid to the adverse effect of the air mass transportation from Bohai Bay.

Phthalic acid esters (PAEs) are a class of common environmental endocrine disruptors (EEDs), capable of causing considerable pollution to water, soil, and air and producing a range of adverse health impacts in humans. Although various studies have investigated the pollution characteristics and health hazards of PAEs in different media, a systematic review of PAEs in the broader environmental context is still lacking. In order to comprehensively explore current issues and suggest prospects, the current status, detection technology, toxicity, and health hazards of PAEs were investigated. The results suggest that PAE pollution is a widespread and complex global phenomenon, transported over long distances. The traditional techniques used for determination include high-performance liquid chromatography–mass spectrometry (HPLC-MS), gas chromatography–mass spectrometry (GC-MS), and high-performance liquid chromatography (HPLC). Various detection techniques offer distinct advantages and disadvantages. Moreover, PAEs can cause differing extents of harm to the nervous and reproductive systems of mammals. In the future, it is imperative to improve the detection of PAEs, establish rapid identification approaches, refine toxicological research methods, and investigate more comprehensive health risk assessment methods. These efforts will provide scientific support for the prevention and management of the resulting contaminants.

In recent years, the concentrations of PM_2.5 in urban ambient air in China have been declining; however, the strong atmospheric oxidation capacity (AOC) represents challenges to the further reduction of PM_2.5 concentration and the continuous improvement of ambient air quality in China in the future, since the overall AOC is still at a high level. For this paper, based on ground observation data recorded in Beijing from 2016 to 2019, the variation in AOC was characterized according to the concentration of odd oxygen (O_X = O₃ + NO₂). The concentrations of the primary and secondary components of PM_2.5 were analyzed using empirical formulas, the correlation between AOC and the concentrations of secondary PM_2.5 and the secondary inorganic components (SO₄²⁻, NO₃⁻, NH₄⁺, and SNA) in Beijing were explored, the impact of atmospheric photochemical reaction activity on the generation of atmospheric secondary particles was evaluated, and the impact of atmospheric oxidation variations on PM_2.5 concentrations and SNA in Beijing was investigated. The results revealed that O_X concentrations reached their peak in 2016 and reached their lowest point in 2019. The O_X concentrations followed a descending seasonal trend of summer, spring, autumn, and winter, along with a spatial descending trend from urban observation stations to suburban stations and background stations. The degree of photochemical activity and the magnitude of the AOC have a large influence on the production of atmospheric secondary particles. When the photochemical reaction was more active and the AOC was stronger, the mass concentrations of the secondary generated PM_2.5 fraction were higher and accounted for a higher proportion of the total PM_2.5 mass concentrations. In the PM_2.5 fraction, SNA accounted for 50.7% to 94.4% of the total mass concentrations of water-soluble inorganic ions in the field observations. Higher concentrations of the atmospheric oxidant O_X in ambient air corresponded to a higher sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR), suggesting that the increase in AOC could promote the increase of PM_2.5 concentration. Based on a relationship analysis of SOR, NOR, and O_X, it was inferred that the relationship between O_X and SOR and the relationship between O_X and NOR were both nonlinear. Therefore, when establishing PM_2.5 control strategies in Beijing in the future, the impact of the AOC on PM_2.5 generation should be fully considered, and favorable measures should be taken to properly regulate the AOC, which would be more effective when carrying out further control measures regarding PM_2.5 pollution.

Understanding the correlation between PM_2.5 and O₃ is critical for complex air pollution control. This study comprehensively analyzed PM_2.5 and O₃ pollution characteristics, uncovered spatiotemporal variations in their correlation, and investigated the driving mechanisms of their association in Dongying, a typical petrochemical city in China’s Bohai Bay region. Results showed that PM_2.5–O₃ correlation in Dongying exhibited significant seasonal variations, spatial patterns, and concentration threshold effects from 2017 to 2023. PM_2.5 and O₃ showed strong positive correlations in summer, negative in winter, and weak positive in spring/autumn, with strongest links in western areas. The strongest positive PM_2.5–O₃ correlation occurred in summer when PM_2.5 ≤ 35 μg·m⁻³ and O₃ >160 μg·m⁻³, while the strongest negative correlation was exhibited in winter with PM_2.5 > 75 μg·m⁻³ and O₃ ≤ 100 μg·m⁻³. Meteorological conditions (T > 20 °C, RH < 30%, wind speed < 1.73 m/s, O_x > 125 μg·m⁻³) and non-sea-breeze periods enhanced the PM_2.5–O₃ positive correlation. During the four typical pollution episodes, the positive PM_2.5–O₃ correlation in summer was propelled by synchronous increases in O₃ and secondary components via shared precursors. In autumn, strong positivity resulted from secondary component–O₃ correlations (r > 0.7) and dominance of secondary formation in PM_2.5. In winter, the negative correlation stemmed from primary emissions inhibiting photochemistry. Random forest analysis showed that O_x, RH, and T drove positive PM_2.5–O₃ correlation via photochemistry in summer, whereas winter primary emissions and NO titration caused negative correlation. This study offers guidance for the collaborative PM_2.5 and O₃ control in the petrochemical cities of the Bay region.

Over the past decade, China’s air quality has improved significantly. To further mitigate the concentration levels of fine particulate matter (PM_2.5), this study analyzed the spatio-temporal evolution of PM_2.5 concentrations from 2012 to 2022. Furthermore, the study integrated the generalized additive model (GAM) and GeoDetector to investigate the main driving factors and explored the complex response relationships between these factors and PM_2.5 concentrations. The results showed the following: (1) The annual average concentration of PM_2.5 in China peaked in 2013. The annual reductions of PM_2.5 in each city ranged from 1.48 to 7.33 μg/m³. In each year, the PM_2.5 concentrations were always consistently higher in north and east China and lowest in northeast and southwest China. (2) In terms of spatial distribution, the North China Plain, the Middle and Lower Yangtze River Plain, and the Sichuan Basin exhibited the highest PM_2.5 concentration levels and showed high aggregation characteristics. (3) The GeoDetector analysis identified the concentrations of SO₂, NO₂, and CO and the meteorological conditions as important factors influencing the spatial differentiation of PM_2.5. The results of the GAM showed that the meteorological factors, such as temperature, atmospheric pressure, wind speed, and precipitation, generally had specific inflection points in their effects on the PM_2.5 concentration levels. The relationship of PM_2.5 with the gross domestic product and population density followed an inverted U shape. The PM_2.5 concentrations under the land use types of cropland, barren, impervious, and water were higher than others. The concentration of PM_2.5 decreased significantly under all land use types. Our work can be used as a strong basis for providing insights crucial for developing long-term pollution control strategies and promoting environmental sustainability.