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

Biochar application strategies mediating the soil temperature, moisture and salinity during the crop seedling stage in Mollisols

It is well known that biochar remarkably changes the fertility and quality in degraded soils, however, it's still not clear how homogeneous application (HA) and bottom concentrated application of biochar (CA) influences soil moisture (SM), soil temperature (ST) and salts during crops seedling stage. In this study, both HA and CA combining with four levels of 0 (CK), 10 (CA1/HA1), 20 (CA2/HA2) and 40 t ha-1 (CA3/HA3) were used to reveal how biochar affects SM, ST and soil electrical conductivity (EC) at seedling stage (spring) of maize in moderately degraded Mollisols. The results showed that, the speed of daily ST increase was only significantly slower in CA1 than in CK during the warming stage, performing a "hysteresis effect". Compared with CK, SM and EC were significantly reduced by 32.9 % and 52.9 % in CA3, while increased by 30.4 % and 20.7 % in HA3 during the whole seedling stage. Between the SM/EC and biochar application amount, there was a negative linear relationship in CA, while was a quadratic function relationship in HA during the whole seedling stage. SM (14.49-29.72 %), EC (0.15-0.38 ms cm-1) and ST (14.86-19.31 °C) were higher in CA1 and HA3 than other treatments in rainfall and drought conditions. DSSA-CERES-maize model adequately simulated the effect of biochar on ST change during maize seedling (nRMSE≤22.6 %, d ≥ 0.59) by integrating initial soil conditions, meteorological data, crop management data, and soil physicochemical properties and crop growth indexes affected by biochar. Generally, HA3 and CA1 was beneficial for improving soil water retention and reducing salt ion leaching, while CA3 accelerated soil drought and increased salt ion leaching during maize seedling stage in Mollisols. The results of this study can provide guidance for the application of crop models in biochar application.

Public preferences and willingness to pay for environmental benefits of straw return: Empirical evidence from Northeast China

Straw management is an important issue for many developing countries. In China, straw return is an effective way of straw management, involving substantial financial subsidies and impacts on public welfare through environmental improvements. The public plays a significant role as a financial source and beneficiary, and sustainable straw return policies need to respond to the public's interests and concerns. Assessments of the public's heterogeneous preferences and willingness to pay can provide useful social insights into straw return policies. However, public opinion has not received sufficient attention. To fill this gap, this study utilized random parameter logit and latent class models based on a choice experiment survey data to assess willingness to pay and preference heterogeneity for environmental benefits of straw return. The results show that urban residents were willing to pay 20.71 CNY, 17.37 CNY, and 11.79 CNY, respectively, for increasing 1% soil organic matter content, clean air days, and chemical fertilizer reduction through straw return. Respondents' preferences were significantly influenced by their socioeconomic and cognitive characteristics. Specifically, respondents with higher income and more understanding of straw return policy have a significant preference for more attributes; older, lower-income, and less understanding groups have a significant preference for fewer attributes. The findings will not only enhance the accuracy and effectiveness of straw return policies, helping to form sustainable straw return policies, but also highlighting the necessity of broadening the scope of analysis for sustainable agricultural practices to provide a more comprehensive assessment, especially for developing countries facing straw management problems.

Low-condensation diesel use contributes to winter haze in cold regions of China

The application of low-condensation diesel in cold regions with extremely low ambient temperatures (-14 to -29 °C) has enabled the operation of diesel vehicles. Still, it may contribute to heavy haze pollution in cold regions during winter. Here we examine pollutant emissions from low-condensation diesel in China. We measure the emissions of elemental carbon (EC), organic carbon (OC), and elements, including heavy metals such as arsenic (As). Our results show that low-condensation diesel increased EC and OC emissions by 2.5 and 2.6 times compared to normal diesel fuel, respectively. Indicators of vehicular sources, including EC, As, lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), and manganese (Mn), increased by approximately 20.2-162.5% when using low-condensation diesel. Seasonal variation of vehicular source indicators, observed at road site ambient environments revealed the enhancement of PM2.5 pollution by the application of low-condensation diesel in winter. These findings suggest that -35# diesel, a low-cetane index diesel, may enhance air pollution in winter, according to a dynamometer test conducted in laboratory. It raises questions about whether higher emissions are released if -35# diesel is applied to running vehicles in real-world cold ambient environments.

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.

Identification and contribution of potential sources to atmospheric lead pollution in a typical megacity: Insights from isotope analysis and the Bayesian mixing model

Atmospheric particulate matter (PM) enriched with lead (Pb) has severe irreversible effects on human health. Therefore, identifying the contribution of Pb emission sources is essential for protecting the health of residents. Using the Pb isotopic tracer method, this study explored the seasonal characteristics and primary anthropogenic Pb sources for atmospheric PM in Tianjin in 2019. We calculated the contribution of Pb sources using the end-member and MixSIAR models. The results showed that Pb loaded in PM10 was more abundant in January than in July, and was strongly influenced by meteorological conditions and anthropogenic emissions. The primary Pb sources of the aerosol samples originated from coal combustion and vehicle and steel plant emissions, mainly originating from local Pb emission sources in Tianjin. The PM10-bond Pb in January was influenced by regional transportation and local sources. The MixSIAS model calculated the contribution of coal combustion as approximately 50 %. Compared with that in January, the contribution of coal combustion decreased by 9.6 % in July. Our results indicate that some of the benefits of phased-out leaded gasoline have been short-lived, whereas other industrial activities releasing Pb have increased. Furthermore, the results emphasise the practicability of the Pb isotope tracer source approach for identifying and distinguishing between different anthropogenic Pb inputs. Based on this study, scientific and effective air pollution prevention and control programs can be formulated to provide decision support for the guidance and control of air pollutant emissions.

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.