Investigating the effect of sources and meteorological conditions on wintertime haze formation in Northeast China: A case study in Harbin

Pollution characteristics, source apportionment and absorption spectra of size-resolved PAHs in atmospheric particles in a cold megacity of China

Polycyclic aromatic hydrocarbons (PAHs) have the capability for solar radiation absorption related to climate forcing. Herein, pollution characteristics and absorption spectra of size-resolved PAHs in atmospheric particles in a cold megacity were comprehensively investigated. The mean concentrations of Σ18PAHs in all the 11 particle size ranges were 3.95 ± 4.77 × 104 pg/m3 and 2.17 ± 1.54 × 103 pg/m3 in heating period (HP) and non-heating period (NHP), respectively. Except for most PAHs with 2 and 3 benzene rings in NHP, most other PAHs showed a unimodal distribution pattern with the peak at 0.56-1.0 µm in both periods, which was caused by PAH emission sources. The PAH-related climate forcing was mainly caused by the solar radiation absorptions at ∼325 (∼330) nm and ∼365 nm. In general, the absorption intensities were higher in HP than NHP. The absorption intensity in the particle size range of 0.56-1.0 µm was the highest, and benzo[e]pyrene was the dominant contributor. In colder periods in HP, higher PAH concentrations caused more intensive PAH-related climate forcing. This study provided new insights for pollution characteristics and absorption spectra of size-resolved PAHs in atmospheric particles, which will be useful for better understanding PAH-related climate forcing.

Exploring efficient strategies for air quality improvement in China based on its regional characteristics and interannual evolution of PM2.5 pollution

Fine particulate matter (PM2.5) harms human health and hinders normal human life. Considering the serious complexity and obvious regional characteristics of PM2.5 pollution, it is urgent to fill in the comprehensive overview of regional characteristics and interannual evolution of PM2.5. This review studied the PM2.5 pollution in six typical areas between 2014 and 2022 based on the data published by the Chinese government and nearly 120 relevant literature. We analyzed and compared the characteristics of interannual and quarterly changes of PM2.5 concentration. The Beijing-Tianjin-Hebei region (BTH), Yangtze River Delta (YRD) and Pearl River Delta (PRD) made remarkable progress in improving PM2.5 pollution, while Fenwei Plain (FWP), Sichuan Basin (SCB) and Northeast Plain (NEP) were slightly inferior mainly due to the relatively lower level of economic development. It was found that the annual average PM2.5 concentration change versus year curves in the three areas with better pollution control conditions can be merged into a smooth curve. Importantly, this can be fitted for the accurate evaluation of each area and provide reliable prediction of its future evolution. In addition, we analyzed the factors affecting the PM2.5 in each area and summarize the causes of air pollution in China. They included primary emission, secondary generation, regional transmission, as well as unfavorable air dispersion conditions. We also suggested that the PM2.5 pollution control should target specific industries and periods, and further research need to be carried out on the process of secondary production. The results provided useful assistance such as effect prediction and strategy guidance for PM2.5 pollution control in Chinese backward areas.

Outdoor Health Risk of Atmospheric Particulate Matter at Night in Xi'an, Northwestern China

The deterioration of air quality via anthropogenic activities during the night period has been deemed a serious concern among the scientific community. Thereby, we explored the outdoor particulate matter (PM) concentration and the contributions from various sources during the day and night in winter and spring 2021 in a megacity, northwestern China. The results revealed that the changes in chemical compositions of PM and sources (motor vehicles, industrial emissions, coal combustion) at night lead to substantial PM toxicity, oxidative potential (OP), and OP/PM per unit mass, indicating high oxidative toxicity and exposure risk at nighttime. Furthermore, higher environmentally persistent free radical (EPFR) concentration and its significant correlation with OP were observed, suggesting that EPFRs cause reactive oxygen species (ROS) formation. Moreover, the noncarcinogenic and carcinogenic risks were systematically explained and spatialized to children and adults, highlighting intensified hotspots to epidemiological researchers. This better understanding of day-night-based PM formation pathways and their hazardous impact will assist to guide measures to diminish the toxicity of PM and reduce the disease led by air pollution.

Size-resolved environmentally persistent free radicals in cold region atmosphere: Implications for inhalation exposure risk

Environmental persistent free radicals (EPFRs) have attracted more attentions recently due to their potential adverse effects to human. EPFRs in full-size range particles were comprehensively investigated in this study. The average EPFRs concentration during heating season was 3.01 × 10¹⁴ spins/m³, which was much higher than that in non-heating season (4.30 × 10¹³ spins/m³). The highest concentration of EPFRs presented in 0.56-1.0 µm particles during heating season, while it shifted to 5.6-10 µm particles during non-heating season. Besides, the contributions of EPFRs on PM_>10 to the total concentration of EPFRs cannot be neglected, especially in the non-heating season. The International Commission on Radiological Protection model and the specific factors of the Chinese population were applied to evaluate the inhalation exposure risk of EPFRs. The results indicated that the exposure levels of EPFRs to the upper respiratory tract were much higher. The daily exposure dose of EPFRs suggested the inhalation exposure risk of 3-4 years old was higher than other age groups. In summary, these finding provided new insights for the full range particle size distribution and the inhalation exposure risk of EPFRs, which improved our understanding on the environmental fate and the health risk of EPFRs in atmosphere.

Value conflicts in grassroots environmental management from a network perspective: a case study of crop residue management in Harbin, China

Open burning of crop residue is a hot issue in Asia and has attracted widespread attention. However, this attention rarely extends to the complex interactions between multi-stakeholders in the governance process, which is precisely the focus of today's environmental governance dilemma. Harbin is a major grain-producing area in China, the annual air pollution caused by the open burning of crop straw is more prominent than in other parts of China, and the conflicting relationships among multi-stakeholders are also typical. Taking Harbin as a case, this study quantifies the complex relationships among stakeholders through value demands conflicts and constructs a value conflict network in the context of straw governance. Through the analysis of the network nodes and relationships, we found that grassroots governments and farmers are the core of the conflict, while public and higher-level governments, as supervisory subjects, are marginalized. The multiple identities and value demands of the grassroots government, as well as cost and technology constraints, are the main reasons for the governance dilemma. In addition, the grassroots government in different scenario dimensions has different conflict resolution strategies, and it has a strong self-adaptation ability in the embedded value conflict network and can influence and reshape other stakeholders. These findings highlight the critical role of the grassroots government in crop residue governance, add to the research paradigm on grassroots environmental management from a multiple-stakeholder participation perspective, and provide a theoretical and methodological basis to formulate effective strategies.

Heterogeneity of plastic residue was determined by both mulch film and external plastic pollutants in the farmland of Northeast China

Plastic pollution in farmland ecosystems has been widely concerned. However, the heterogeneity and driving mechanisms of plastic residue (PR) remain unclear in the farmland surrounded by complex pollution points. In this study, the abundance, mass, and accumulation areas of PR of mulch film (MF) and non-MF (NMF) were investigated in a large area of the vegetable field covered by plastic mulching in a long-term in Northeast China. Geostatistics combined with classical statistics were used to clarify how pollution source and migration factors change the PR heterogeneity in the farmlands. Results indicated that the MF type was only polyethylene (PE) (79.1 % of total PR), while NMF accounted for 20.9 % of total PR. As well, NMF-polypropylene (PP) and NMF-PE accounted for 45.3 % and 39.7 % of total NMF respectively, followed by polystyrene accounting for 7.5 %. In the 0-20 cm soil layer, the spatial autocorrelation of mass and accumulation areas of MF were significantly (p < 0.05) positive, and their spatial pattern tended to cluster. The accumulation areas of MF was predoniment in northwest and southeast near the roadside in all soil layers, while the accumulation areas of NMF was higher near the landfill in the 0-20 cm soil layer. Landfill and residential areas were critical sources of PR for the farmland. Southwest wind and southeast wind were the main driving force of PR migration and their annual migration rates were 23.7 and 19.8 m·year^-1. The functional groups on the surface of plastics were different after degradation (including different types and different utilization methods), and PR was oxidized could release or adsorb toxic substances from the soils. Generally, in order to reduce PR pollution, in addition to source control and recycling, farmland tillage should be avoided in the weather when the wind speed is strong, especially near the PR pollution source.

Factors Influencing PM2.5 Concentrations in the Beijing–Tianjin–Hebei Urban Agglomeration Using a Geographical and Temporal Weighted Regression Model

Air pollution is the environmental issue of greatest concern in China, especially the PM2.5 pollution in the Beijing–Tianjin–Hebei urban agglomeration (BTHUA). Based on sustainable development, it is of interest to study the spatiotemporal distribution of PM2.5 and its influencing mechanisms. This study reveals the temporal evolution and spatial clustering characteristic of PM2.5 pollution from 2015 to 2019, and quantifies the drivers of its natural and socioeconomic factors on it by using a geographical temporal weighted regression model. Results show that PM2.5 concentrations reached their highest level in 2015 before decreasing in the following years. The monthly averages all present a U-shaped change trend. Relative to the traditional high concentrations in the northern part of the BTHUA domain in 2015, the gap in pollution between the north and south has reduced since 2018. The obvious spatial heterogeneity was demonstrated in both the strength and direction of the variables. This study may help identify reasons for high PM2.5 concentrations and suggest appropriate targeted control and prevention measures.