Tropospheric ozone (O₃) is a trace gas playing important roles in atmospheric chemistry, air quality and climate change. In contrast to North America and Europe, long-term measurements of surface O₃ are very limited in China. We compile available O₃ observations at Mt. Tai – the highest mountain over the North China Plain – during 2003–2015 and analyze the decadal change of O₃ and its sources. A linear regression analysis shows that summertime O₃ measured at Mt. Tai has increased significantly by 1.7 ppbv yr⁻¹ for June and 2.1 ppbv yr⁻¹ for the July–August average. The observed increase is supported by a global chemistry-climate model hindcast (GFDL-AM3) with O₃ precursor emissions varying from year to year over 1980–2014. Analysis of satellite data indicates that the O₃ increase was mainly due to the increased emissions of O₃ precursors, in particular volatile organic compounds (VOCs). An important finding is that the emissions of nitrogen oxides (NO_x) have diminished since 2011, but the increase of VOCs appears to have enhanced the ozone production efficiency and contributed to the observed O₃ increase in central eastern China. We present evidence that controlling NO_x alone, in the absence of VOC controls, is not sufficient to reduce regional O₃ levels in North China in a short period.

Recent studies have shown that surface ozone (O ₃ ) concentrations over central eastern China (CEC) have increased significantly during the past decade. We quantified the effects of changes in meteorological conditions and O ₃ precursor emissions on surface O ₃ levels over CEC between July 2003 and July 2015 using the GEOS-Chem model. The simulated monthly mean maximum daily 8 h average O ₃ concentration (MDA8 O ₃ ) in July increased by approximately 13.6 %, from 65.5±7.9 ppbv (2003) to 74.4±8.7 ppbv (2015), comparable to the observed results. The change in meteorology led to an increase in MDA8 O ₃ of 5.8±3.9 ppbv over the central part of CEC, in contrast to a decrease of about -0.8±3.5 ppbv over the eastern part of the region. In comparison, the MDA8 O ₃ over the central and eastern parts of CEC increased by 3.5±1.4 and 5.6±1.8 ppbv due to the increased emissions. The increase in averaged O ₃ in the CEC region resulting from the emission increase (4.0±1.9 ppbv) was higher than that caused by meteorological changes (3.1±4.9 ppbv) relative to the 2003 standard simulation, while the regions with larger O ₃ increases showed a higher sensitivity to meteorological conditions than to emission changes. Sensitivity tests indicate that increased levels of anthropogenic non-methane volatile organic compounds (NMVOCs) dominate the O ₃ increase over the eastern part of CEC, and anthropogenic nitrogen oxides (NO _x ) mainly increase MDA8 O ₃ over the central and western parts and decrease O ₃ in a few urban areas in the eastern part. Budget analysis showed that net photochemical production and meteorological conditions (transport in particular) are two important factors that influence O ₃ levels over the CEC. The results of this study suggest a need to further assess the effectiveness of control strategies for O ₃ pollution in the context of regional meteorology and anthropogenic emission changes.

Though the impact of urban vegetation on air quality and the microclimate has attracted increasing attention, there have been few studies quantitatively assessing this impact in North China, where air pollution is severe. In this study, we investigated the impact of urban forests and urban parks on air quality and the microclimate in Jinan, northern China. Six sites were chosen to represent urban forest, urban park, and downtown areas, respectively. The results indicate that urban forest can effectively reduce PM_2.5 and ozone (O₃) concentrations in the warm season, when temperatures are higher and plants are lush. The PM_2.5 and O₃ concentrations in the urban forest areas were 6.3–6.5 μg m⁻³ and 21–23 μg m⁻³ lower than those in downtown areas during the period of 10:00–15:00. In contrast, urban park areas can reduce PM_2.5 concentrations but have little impact on gaseous pollutants such as nitrogen dioxide and O₃. Furthermore, both urban forest and urban park areas reduced temperatures, by approximately 4.1–6.8 °C and 1.36 °C, respectively, and increased relative humidity, by about 13.4–12.9% and 0.9%, promoting a more comfortable thermal environment for residents. Therefore, this study highlights the crucial role of urban vegetation in improving air quality and creating a comfortable environment for residents.

While air quality in China has improved significantly in recent years, the population is becoming increasingly vulnerable to air pollution due to the aging population. In this study, we assessed premature deaths attributable to long- and short-term exposures to PM_2.5 and O₃, as well as their driving forces in Shandong from 2014 to 2060 based on county-level near-real-time air pollutant concentration datasets and projected concentrations of PM_2.5 and O₃. We found that the concentrations of PM_2.5 and O₃ in most districts and counties from Shandong are still higher than the corresponding concentration limit of Grade II. Premature mortality caused by long- and short-term exposures to PM_2.5 decreased by 13,045 and 8092 in 2020 compared with those in 2014, respectively. Furthermore, premature mortality attributable to short-term exposure to O₃ was 36.08% higher than that due to short-term exposure to PM_2.5 in 2020. The results of the driving force analysis indicate that the health benefits brought about by the improvement in air quality have been offset by the changes in population age structure. In the future, the increase in O₃ concentration and population aging are the top two driving forces having adverse effects on the health burden. This study provides support for controlling the health risks of PM_2.5 and O₃ pollution, especially for the development of dual-pollutant concentration targets and synergistic control strategies.

Simultaneous measurements of atmospheric volatile organic compounds (VOCs), conventional gases and meteorological parameters were performed at an urban site in Jinan, East China, in June 2021 to explore the formation and evolution mechanisms of summertime ozone (O₃) pollution events. O₃ Episode Ⅰ, O₃ Episode II, and non-O₃ episodes were identified based on the China Ambient Air Quality Standards and the differences in precursor concentrations. The O₃ concentrations in Episode I and Episode II were 145.4 μg/m³ and 166.4 μg/m³, respectively, which were significantly higher than that in non-O₃ episode (90 μg/m³). For O₃ precursors, VOCs and NOx concentrations increased by 48% and 34% in Episode I, and decreased by 21% and 27% in Episode II compared to non-O₃ episode days. The analysis of the m,p-xylene to ethylbenzene ratio (X/E) and OH exposure demonstrated that the aging of the air masses in Episode II was significantly higher than the other two episodes, and the differences could not be explained by localized photochemical consumption. Therefore, we speculate that the high O₃ concentrations in Episode II were driven by the regional transport of O₃ and its precursors. Backward trajectory simulations indicated that the air masses during Episode II were concentrated from the south. In contrast, the combination of high precursor concentrations and favorable meteorological conditions (high temperatures and low humidity) led to an excess of O₃ in Episode I. Positive matrix factorization (PMF) model results indicated that increased emissions from combustion and gasoline vehicle exhausts contributed to the elevated concentrations of VOCs in Episode I, and solvent usage may be an important contributor to O₃ formation. The results of this study emphasize the importance of strengthening regional joint control of O₃ and its precursors with neighboring cities, especially in the south, which is crucial for Jinan to mitigate O₃ pollution.