This study presents the first nationwide assessment of atmospheric microplastics in China that systematically investigates the sources, distribution patterns, and governing factors of atmospheric microplastics across China through an integrated approach combining: year-round monitoring of both deposited (DAMPs) and suspended atmospheric microplastics (SAMPs) in Ningbo, and nationwide analysis of DAMPs data from 30 cities. Results showed an average DAMP flux of 473.9 f 349.3 items m- 2 d- 1 and SAMP concentration of 0.15 f 0.08 items m- 3 in Ningbo, with an inverse seasonal relationship between SAMPs and DAMPs and a washout ratio of (1.02 f 0.42) x 106 confirming rainfall's crucial role in microplastic removal. Multivariate analysis identified precipitation, temperature, and wind speed as key environmental drivers, while socioeconomic factors including population and GDP per capita strongly influenced spatial distribution of DAMPs. Nationwide analysis of 30 cities also established robust correlations between deposition fluxes and socioeconomic indicators. Based on this strong statistical relationship we developed the first predictive model for China, estimating total annual deposition at 1745 f 619 tonnes, with wealthier coastal regions exhibiting 2.3-5.1 times higher fluxes than inland/less-urban areas. These findings quantify the coupled influence of meteorological and anthropogenic drivers on atmospheric microplastic pollution. This assessment provides a scientific basis for targeted mitigation, suggesting prioritized

Ammonia (NH3) is an important alkaline gas and a key precursor to secondary inorganic aerosol. In the Fen River valley, coking plants are concentrated due to transportation advantages, while NH3 emissions from coking processes have received limited attention despite their potential importance. In this study, atmospheric NH3 was sampled by OGAWA samplers in a typical coal coking industrial park in Taiyuan during autumn and winter of 2024-2025, and its nitrogen isotopic composition was used for source apportionment. The results showed that the NH3 concentration in the industrial park was 27.4 +/- 3.8 mu g m-3, significantly higher than that in the urban area (9.3 +/- 4.2 mu g m-3) and higher than winter levels reported for North China cities. The delta 15N-NH3 was -29.7 +/- 1.6 parts per thousand and increased to -14.7 +/- 1.6 parts per thousand after correcting for passive sampling bias. Source apportionment further indicated that NH3 in the industrial park was dominated by non-agricultural sources (80.7%), with ammonia slip as the largest contributor (34.2 +/- 20.1%), followed by coal combustion (25.8 +/- 16.5%), traffic emissions (20.7 +/- 11.6%) and agricultural sources (19.3 +/- 11.6%). Therefore, some measures should be taken to reduce the NH3 emissions from ammonia slip and traffic during autumn and winter.

Atmospheric nitrate (NO3-), a key component of fine particulate matter (PM2.5), significantly impacts air quality and climate. This study investigates decadal variability (2013-2022) of PM2.5-associated NO3- in Beijing using continuous real-time measurements, meteorological normalization, and source identification. Results reveal an annual NO3- decline of 4.8 %, driven by stringent clean air policies like "coal-to-gas" initiatives, with autumn and winter reductions (-8.6 %/yr and -8.4 %/yr, respectively) outpacing other seasons due to targeted emission controls. Despite progress, NO3- remains elevated (11.7 +/- 15.8 mu g/m(3)), contributing 33.0 % to PM2.5 by 2022, underscoring persistent secondary formation under high oxidation capacity. Diurnal patterns show high nocturnal and morning values (shallow boundary layers and traffic emissions) and minima at 16:00-18:00 (volatilization and deep boundary layers), while absent weekend effects reflect unregulated traffic and sustained residential activity. Meteorological normalization attributes 78.4 % of NO3- decline to emission controls, emphasizing policy efficacy, yet chemical feedbacks (enhanced NOx-to-HNO3 conversion) and transboundary transport challenge further mitigation. The interplay between local emissions and regional transport significantly shaped the variability of PM2.5-associated NO3- in Beijing from 2013 to 2022. The nonparametric wind regression analyses identify northwest and southern hotspots, with shifting source regions post-2018 highlighting growing contributions from southern industrial zones. Based on the potential source contribution function and concentration weighted trajectory methods, it can be found that dominant source regions of NO3- and its precursor (NOx) were located south of Beijing. Findings advocate interaction of policy, chemistry, and meteorology in shaping PM2.5 composition, integrated NH3-NOx controls and regional coordination, offering critical insights for optimizing air quality strategies in rapidly urbanizing regions globally.

Sulfate aerosols formed within industrial plumes, particularly from steel plants, are major sources of atmospheric particles, yet their formation pathways and physicochemical properties remain poorly resolved due to a lack of direct observation. In this study, we employed computer-controlled scanning electron microscopy (CCSEM) to investigate the morphological features, elemental composition, and size distribution of individual particles collected at five sampling sites within a typical steel plant and the surrounding environment. A total of 91,185 individual particles were automatically analyzed and classified, and Na-rich (46.6 %), Ca-rich (21.5 %), and Si-rich (8.2 %) particles were the three major types in number proportions with a wide size range of 0.2–43.6 μm in equivalent diameter. Most notably, elongated submicron Na2SO4 particles accounted for 72.8 % of total particle number nearest the exhaust outlet of the steel plant. These sulfate particles underwent rapid atmospheric aging processes, evidenced by a 96.2 % depositional removal within the plant and a significant increase in average size from 1.1 to 3.4 μm. When transported to the ambient sites outside the plant (6–20 km away), their abundance significantly decreased to only 5.3 % (range: 2.2 %–11.7 %), indicating limited long-term transport. This study provides the first microscopic evidence that inorganic sulfate aerosols exhibit considerable near-source emission but undergo rapid sedimentation. Our findings highlight the significance of sulfate aerosols as a major component of PM2.5 near industrial areas, underscoring the urgent need to control this emission pathway.

Understanding the interplay between emissions and meteorology is critical for air quality management, yet quantifying emission-related changes under unfavorable atmospheric conditions remains challenging. This research employs a natural experiment during the meteorologically demanding 2025 Victory Day military parade to evaluate the effectiveness and meteorological vulnerability of air quality control measures. Analysis of a decade (2016–2025) of high-resolution observed PM2.5 chemical speciation data from Beijing, alongside data from the Beijing–Tianjin–Hebei and its surrounding regions (“2 + 36 cities”), demonstrates substantial and sustained air quality enhancements. The “2 + 36 cities” experienced a 55.9% reduction in mean PM2.5 concentrations and a notable convergence of inter-city variability. Beijing's PM2.5 levels decreased by 50%, with secondary inorganic components, particularly nitrate (NO3−), becoming more prominent. Five major sources were consistently identified by the Positive Matrix Factorization model, with secondary formation and vehicular emissions remaining the most significant contributors. Meteorological normalization reveals that the 33.1% PM2.5 decrease during the 2025 study period, compared to the 2016–2024 baseline, was primarily associated with the anthropogenic-related component (−34.4%), with a minor meteorological contribution (+1.3%). However, on the parade day, stagnant and humid conditions, together with regional transport, resulted in a significant +43.2% meteorological penalty, largely negating the concurrent anthropogenic-related decrease (−35.7%). Furthermore, the meteorology-related contribution increased secondary inorganic components by 41.1%, counteracting their anthropogenic decline (−40.3%). This study provides evidence for an adaptive, sustainable air quality management framework in regions where secondary particulate pollution can be strongly amplified by unfavorable meteorological conditions.

While the solubility of atmospheric elements critically influences their toxicity and environmental mobility, global understanding of water-soluble hazardous elements (WSHEs) in PM2.5 remains limited. To address this, PM2.5 samples were collected from July 2021 to March 2022 across six major cities in the Beijing-Tianjin-Hebei region and its surroundings (BTHs). Total elemental concentrations (all cities) and water-soluble fractions (Beijing) were quantified via inductively coupled plasma mass spectrometry (ICP-MS), focusing on Cd, V, Cr, Ni, Se, As, Mn, and Pb. Regional analyses revealed synchronized pollution patterns across BTHs, driven by shared industrial/energy activities. In Beijing, WSHEs constituted 25.0-39 .3 % of total concentrations, with Cd (35.7 %) and Mn (39.3 %) showing peak solubility. WSHE levels rose during air quality deterioration but declined during dust storms due to crustal sources with low solubility. Key drivers of solubility included particle acidity, liquid water content, and organic carbon, emphasizing atmospheric processing (e.g., acid dissolution) as a bioaccessibility amplifier. Positive Matrix Factorization identified vehicular emissions (38 %) and coal combustion (20 %) as dominant WSHE sources, followed by waste incineration (20 %), metal smelting (14 %), electronics manufacturing (6 %), and dust (2 %). Coal and vehicular sources contributed disproportionately to bioaccessible elements, whereas dust-derived elements exhibited minimal solubility. These results highlight the elevated health risks from anthropogenic WSHEs and the urgency of prioritizing sector-specific controls (e.g., accelerating vehicle electrification, phasing out residential coal) over broad PM2.5 reduction strategies. The study establishes a mechanistic link between emission sources, atmospheric aging, and elemental bioaccessibility, offering actionable insights for mitigating toxic elements exposure in megacities.

Ammonia (NH3) is a significant precursor for secondary inorganic aerosol, in order to better study the impacts of NH3 on PM2.5 pollution in Fenwei Plain in China, hourly-resolved NH3 and water-soluble ions (WSI) were measured at an urban site in Taiyuan from 1 December 2021 to 30 November 2022. Hourly NH3 concentrations ranged from 0.7 to 40.2 mu g m(-3), with an average concentration of 10.2 +/- 5.0 mu g m(-3). Due to the impacts of meteorology and emission sources, NH3 exhibited apparent seasonal variations: summer > autumn > spring > winter. Diurnal variations of NH3 concentrations showed higher values during the daytime except in autumn. Cluster analysis of backward trajectories suggested that the southern short-distance air mass from Taiyuan Basin had the highest concentrations of TNHx (NH3+NH4+) and PM2.5. The analysis by conditional probability function and weighted concentration weighted trajectory function showed the rough consistency between the distribution of the TNHx and PM2.5 in four seasons. The analysis of hourly excess NH3 showed that Taiyuan's atmosphere was always ammonia-sufficient. SOR (nSO(4)(2-)/(nSO(4)(2-) + nSO(2))) and NOR (nNO(3)(-)/(nNO(3)(-) + nNO(2))) increased with NHR (nNH(3)/(nNH(4)(+)+nNH(3)); n denotes the molar concentration) and RH in four seasons, indicating that the gas-particle conversion of NH3 promoted the formation of SO42- and NO3- under high RH condition. The critical total ammonia concentrations (CTACs) in spring, summer, autumn, and winter were 63 %, 61 %, 60 %, and 53 %, respectively. Considering the current difficulty in reducing NH3 and WSI concentration decreased linearly with the reduction of TNO3 (NO3- + HNO3), controlling NOx emissions is more effective for PM2.5 pollution mitigation in Taiyuan.

Scientific knowledge on the chemical compositions of fine particulate matter (PM2.5) is essential for properly assessing its health and climate effects, and for decisionmakers to develop efficient mitigation strategies. A high-resolution PM2.5 chemical composition dataset (CAQRA-aerosol) is developed in this study, which provides hourly maps of organic carbon, black carbon, ammonium, nitrate, and sulfate in China from 2013 to 2020 with a horizontal resolution of 15 km. This paper describes the method, access, and validation results of this dataset. It shows that CAQRA-aerosol has good consistency with observations and achieves higher or comparable accuracy with previous PM2.5 composition datasets. Based on CAQRA-aerosol, spatiotemporal changes of different PM2.5 compositions were investigated from a national viewpoint, which emphasizes different changes of nitrate from other compositions. The estimated annual rate of population-weighted concentrations of nitrate is 0.23 µg m−3 yr−1 from 2015 to 2020, compared with −0.19 to −1.1 µg m−3 yr−1 for other compositions. The whole dataset is freely available from the China Air Pollution Data Center ( https://doi.org/10.12423/capdb_PKU.2023.DA ).

PM2.5 oxidative potential (OP), a key driver of health risks, was investigated in Ningbo, China, using dual dithiothreitol (DTT) and ascorbic acid (AA) assays combined with machine learning (ML). This approach accounts for the complexity of interactions among key chemical drivers and accurately identifies chemical species and PM2.5 sources associated with OP - a critical gap in prior studies relying solely on correlation analysis and linear regression. Year-long PM2.5 samples revealed higher nighttime and summer OP (volume-based OP-DTTv and OP-AAv), linked to aerosol acidity and photochemical aging. Among six ML models, Extremely Randomized Trees (ERT) outperformed others by 9.5-30.7 %, identifying Cu, Fe, V, As, Co, Cd, NO3-, Ni, and quinones as primary OP drivers, with synergistic effects for most constituents except antagonistic Fe. Source apportionment attributed OP mainly to vehicular emissions (40 %), marine/sea salt (20 %), and secondary aerosols (16 %). Biomass burning, industry, and road dust contributed minimally. Results emphasize targeting quinones, traffic-related metals (Cu, V), and synergistic metal interactions to mitigate PM2.5 toxicity in coastal cities. The dual-assay ML framework provides actionable insights for prioritizing OP-driven regulation, particularly in regions blending anthropogenic and marine influences, to reduce oxidative stress-related health burdens.

The component-based potency factor approach, combined with benzo[a]pyrene (BaP) unit risk values from the World Health Organization (WHO), is commonly used to assess lung excess cancer risk (LECR) from polycyclic aromatic hydrocarbons (PAHs). However, this method may overestimate LECR, particularly when highly carcinogenic PAHs are included. In this study, we employed BaP unit risk values from both the WHO and the Environmental Protection Agency (EPA) to estimate LECR in Ningbo, China, revealing that incorporating high-carcinogenic PAHs into the component-based potency factor approach, along with WHO unit risk factors, leads to an overestimation of LECR by more than tenfold. We identified a moderate PAH exposure risk level (>1.0 ×10⁻⁶) in Ningbo and used advanced machine learning (ML) algorithms, random forest (RF), extremely randomized trees (ERT), and extreme gradient boosting (XGBoost), to improve the accuracy of source-specific LECR assessments. ERT emerged as the most robust algorithm, identifying industrial emissions, coal combustion, and gasoline engine exhaust as the primary contributors to elevated LECR in Ningbo. This study underscores the need for precise, source-specific LECR estimation to effectively mitigate PAH pollution and reduce lung cancer risks. By integrating ML techniques into risk assessment methodologies, we provide a robust framework for global application, enhancing public health protection. Our findings also highlight the importance of refining risk evaluation strategies and pave the way for future research to validate and adapt these models in diverse environmental settings.

Despite significant improvements in particulate pollution, ozone (O₃) levels have unexpectedly worsened in Shandong Province, China (SDP), which is one of the world’s hotspots for O₃ pollution. This review aims to summarize O₃ pollution studies in SDP and highlight the challenges faced by current research efforts. The interaction between O₃ chemistry and meteorological conditions has exacerbated O₃ pollution in SDP, with frequent increases in nighttime O₃ levels. Both local emissions and regional transport play significant roles in O₃ pollution, with O₃ production being particularly sensitive to VOCs in most cities. The worsening O₃ pollution has led to increased health risks and ecological damage. This review provides a comprehensive overview of O₃ pollution in SDP, covering formation mechanisms, in-situ measurements, source analyses, and the health and ecological impacts. It is recommended that monitoring networks be scientifically optimized, urgent mitigation strategies for VOCs and NOx be implemented, and collaborative research efforts be intensified to address O₃ pollution at regional scales.

Although particulate Fe has a significant impact on human health, atmospheric chemical reactions, air quality, climate change, and ecosystems, there is a lack of long-term continuous hourly observation on particulate Fe in the megacity of Beijing, limiting research on these issues. To address this gap, this study continuously measured hourly concentrations of Fe in PM2.5 from October 2018 to October 2022 in Beijing. The results indicate an overall decline in Fe concentrations, consistent with previous studies in Beijing. This decline can be attributed to multiple factors, such as reduced coal consumption, restrictions on biomass burning, increased use of clean energy, advanced technologies for industrial emission reduction, and efforts to control fugitive dust. Seasonal variations in Fe concentrations were similar across the various years, with higher mean concentrations in spring, fall, and winter, and lower levels in summer. Daily variations in PM2.5-bound Fe concentrations exhibited two peaks, influenced by changes in emission intensity and the evolution of the planetary boundary layer. The solubility of PM2.5-bound Fe exhibited a wide range, varying from 4 % to 95 %, surpassing previously reported source-specific values. This variability can be attributed to acid dissolution effects and complexation behaviors. Nonparametric wind regression analysis identified distinct hotspots (higher concentrations) in the northwest wind sector at wind speeds of approximately 5-15 km/h, which are associated with blowing dust and dust storms. Additionally, the potential source contribution function analysis identified high-potential source areas were precisely located in the northwestern, western, and southern regions of Beijing, rather than primarily in the southern areas recorded in a previous study. This research provides valuable insights for studying the health effects and migration and transformation of nutrient elements, particularly particulate Fe, in Beijing.

Dust storms have the ability to transport and deposit contaminants and nutrients, such as iron (Fe), to downwind regions through atmospheric processes. However, there is a lack of reported data on the high-resolution variations and deposition of particulate iron in multiple locations during dust storms. This study aimed to address this gap by employing standardized analytical methods to measure the concentrations of PM10, PM2.5, and PM2.5- associated Fe in Taiyuan, Beijing, Tianjin, Ji'nan, and the Bohai Bay of China during the dusty events of 2021. A total of 13 blowing sand or dust storms were recorded, with average PM10 and PM2.5 concentrations of 262 +/- 322 and 85 +/- 652, 171 +/- 403 and 53 +/- 448, 153 +/- 211 and 57 +/- 315, and 207 +/- 249 and 63 +/- 301 mu g/m3 at the above-mentioned sites, respectively. These elevated concentrations were attributed to stronger winds in northern China and severe wind erosion in the sand source areas. During these events, the average concentrations of PM2.5-bound Fe reached 2730.2 +/- 4587.9, 2030.2 +/- 3877.9, 1342.1 +/- 2251.4, and 1785.1 +/- 2536.6 ng/m3 in Taiyuan, Beijing, Tianjin, and Ji'nan, respectively, with the highest concentrations recorded as 48.8, 48.0, 29.2, and 22.7 mu g/m3. A significant positive correlation was observed between Fe and Si in PM2.5 in the four cities, with higher Fe/Si slopes recorded in or near the source regions, while the homogenized Fe/Si values were observed after long-distance transport. The mean dry deposition fluxes (FFe) of PM2.5-bound Fe were calculated as 0.34 +/- 0.64, 0.31 +/- 0.91, 0.21 +/- 0.56, and 0.17 +/- 0.28 mg/m2/d for Taiyuan, Beijing, Tianjin, and Ji'nan, respectively, based on both hourly observation data and model-based calculations of dry deposition velocities. It is worth noting that FFe decreased from west to east in China, consistent with a previous study that showed a decrease in dust deposition rates with increasing transport distances. Peaks in FFe corresponded to the highest concentrations of PM2.5-associated Fe, indicating that these concentrations played a significant role in Fe. Furthermore, the atmospheric deposition of dissolved Fe from blowing sand or dust storm events was found to contribute to carbon fixation in the Bohai region of China, providing a range of 7.8 x 104-3.9 x 106 mol. This research provides valuable insights into the quantitative relationship between atmospheric deposition and marine productivity during dust events.

Situated in close proximity to the Korea Peninsula and the Japan Islands, Shandong Province in China (SDP) has emerged as a focal point for global attention due to its significant surface ozone (O3) and aerosol pollution. Despite this attention, there are notable gaps in knowledge across various interconnected research domains, encompassing climate change, atmospheric circulation, anthropogenic emissions, and the chemistry of O3 and aerosols. The impact of frequent heat waves on regional O3 and aerosol pollution remains unclear, while our comprehension of atmospheric circulation dynamics and the chemistry involved with O3 and aerosols is still hampered by substantial limitations. The unique topography and geographical setting of SDP, with its complex interplay of factors like sea-land breezes, mountain-valley winds, and urban heat islands, make it an ideal location for investigating the dynamics of O3 and aerosol chemistry. Moreover, it is essential to explore the effects of transboundary transport on O3 and aerosol pollution and delve into the underlying mechanisms contributing to their combined pollution effects. To bridge these knowledge gaps, the Innovative Collaboration-Based Ozone and Aerosol Observation Network in Northeast Asia has been established through collaborative efforts involving the Bureaus of Ecology and Environment, Meteorology in SDP, and the Chinese Academy of Sciences. This network encompasses various components, including air quality and weather stations, a network of low-cost air quality sensors, monitoring stations focused on atmospheric photochemical smog and aerosol chemical speciation, and vertical measurement systems targeting O3 and its precursor gases (utilizing light detection and ranging, balloon sounding, and drone-based measurements), as well as measurements conducted via vehicles and ships. Additionally, preliminary findings from this comprehensive observational campaign will be shared. SIGNIFICANCE STATEMENT: This research aims to understand how climate change, atmospheric circulation, and pollution from ozone and aerosols interact in northeast Asia, particularly in Shandong Province. By establishing a comprehensive observation network, we seek to uncover the dynamics of air pollution in diverse environments. Our work provides crucial data to improve air quality and inform climate change mitigation strategies, emphasizing the importance of interdisciplinary collaboration and sustained monitoring efforts to address environmental challenges. This initiative not only enhances scientific understanding but also fosters regional cooperation and contributes significantly to global atmospheric science.

Aerosol chemistry in China has undergone significant transformation due to stringent emission control measures, leading to great shifts in aerosol composition and formation mechanisms. This study investigates the summer chemical evolution of aerosol species in Beijing over the past decade based on two summertime measurements using aerosol chemical speciation monitors. The results reveal a substantial decrease in fine particulate matter concentrations by 72.7% in summer over the past decade, particularly primary species that dropped by 86.3%-95.1%. However, this improvement in particulate matter was accompanied by a worsening of ozone pollution between 2011 and 2022. In contrast, secondary components such as sulfate and secondary organic aerosol (SOA) exhibited significant increases in their contributions, rising from 18.2%-25.5% to 21.4%-41%. The varying responses of aerosol species to emission reductions are closely tie to changes in emission sources, aerosol chemistry, and meteorology. By decoupling the influence of meteorology through machine learning, our analysis highlights the crucial role of emission reductions in improving air quality, though with different impacts on aerosol chemistry. The dominant formation mechanisms of secondary components varied between the two summers, likely influenced by shifts in aerosol liquid water content and atmospheric oxidation capacity due to NOx reductions. Compared to the summer of 2011, the formation of sulfate and SOA in summer 2022 was primarily driven by photochemical processes related to ozone, with less impacts from aqueous-phase formation, while nitrate was predominantly formed via N2O5 heterogeneous hydrolysis. Considering the complex nature of secondary aerosol formation, future summer pollution control strategies should prioritize stricter collaborative regulation of precursors for both secondary aerosol and ozone.

Organic aerosols (OA) constitute an important fraction of fine particulate matter (PM2.5), yet accurate and efficient OA modeling within chemical transport models (CTM) remains a challenge. Volatility basis set (VBS)...