Inhalation of respirable silica particles can cause serious lung diseases (e.g., silicosis and lung cancer), and the toxicity of respirable silica is highly dependent on its crystal form. Common combustion processes such as coal and biomass burning can provide high temperature environments that may alter the crystal forms of silica and thus affect its toxic effects. Although crystalline silica (i.e., quartz, tridymite, and cristobalite) were widely found at different temperatures during the burning processes, the sources and crystal transformation pathways of silica in the burning processes are still not well understood. Here, we investigate the crystal transformation of silica in the coal and biomass combustion processes and clarify the detailed transformation pathways of silica for the first time. Specifically, in coal burning process, amorphous silica can transform into quartz and cristobalite starting at 1100 °C, and quartz transforms into cristobalite starting at 1200 °C; in biomass burning process, amorphous silica can transform into cristobalite starting at 800 °C, and cristobalite transforms into tridymite starting at 1000 °C. These transformation temperatures are significantly lower than those predicted by the classic theory due to possibly the catalysis of coexisting metal elements (e.g., aluminum, iron, and potassium). Our results not only enable a deeper understanding on the combustion-induced crystal transformation of silica, but also contribute to the mitigation of population exposure to respirable silica.

Ground-based Multi-Axis Differential Optical Absorption Spectroscopy (Max-DOAS) measurements of nitrogen dioxide (NO₂) were continuously obtained from January to November 2019 in northeastern China (NEC). Seasonal variations in the mean NO₂ vertical column densities (VCDs) were apparent, with a maximum of 2.9 × 10¹⁶ molecules cm⁻² in the winter due to enhanced NO₂ emissions from coal-fired winter heating, a longer photochemical lifetime and atmospheric transport. Daily maximum and minimum NO₂ VCDs were observed, independent of the season, at around 11:00 and 13:00 local time, respectively, and the most obvious increases and decreases occurred in the winter and autumn, respectively. The mean diurnal NO₂ VCDs at 11:00 increased to at 08:00 by 1.6, 5.8, and 6.7 × 10¹⁵ molecules cm⁻² in the summer, autumn and winter, respectively, due to increased NO₂ emissions, and then decreased by 2.8, 4.2, and 5.1 × 10¹⁵ molecules cm⁻² at 13:00 in the spring, summer, and autumn, respectively. This was due to strong solar radiation and increased planetary boundary layer height. There was no obvious weekend effect, and the NO₂ VCDs only decreased by about 10% on the weekends. We evaluated the contributions of emissions and transport in the different seasons to the NO₂ VCDs using a generalized additive model, where the contributions of local emissions to the total in the spring, summer, autumn, and winter were 89 ± 12%, 92 ± 11%, 86 ± 12%, and 72 ± 16%, respectively. The contribution of regional transport reached 26% in the winter, and this high contribution value was mainly correlated with the northeast wind, which was due to the transport channel of air pollutants along the Changbai Mountains in NEC. The NO₂/SO₂ ratio was used to identify NO₂ from industrial sources and vehicle exhaust. The contribution of industrial NO₂ VCD sources was >66.3 ± 16% in Shenyang due to the large amount of coal combustion from heavy industrial activity, which emitted large amounts of NO₂. Our results suggest that air quality management in Shenyang should consider reductions in local NO₂ emissions from industrial sources along with regional cooperative control.

The health effects of potentially toxic elements (PTEs) in airborne particulate matter (PM) are strongly dependent on their size distribution and dissolution. This study examined PTEs within nine distinct sizes of PM in a Chinese megacity, with a focus on their deposited and dissolved bioaccessibility in the human pulmonary region. A Multiple Path Particle Dosimetry (MPPD) model was used to estimate the deposited bioaccessibility, and an in-vitro experiment with simulated lung fluid was conducted for dissolved bioaccessibility. During the non-heating season, the dissolved bioaccessible fraction (DBF) of As, Cd, Co, Cr, Mn, Pb and V were greater in fine PM (aerodynamics less than 2.1 μm) than in coarse PM (aerodynamics between 2.1 and 10 μm), and vice versa for Ni. With the increased demand of heating, the DBF of Pb and As decreased in fine particle sizes, probably due to the presence of oxide/silicate compounds from coal combustion. Inhalation health risks based on the bioaccessible concentrations of PTEs displayed the peaks in <0.43 μm and 2.1–3.3 μm particulate sizes. The non-cancer risk was at an acceptable level (95th percentiles of hazard index (HI) was 0.49), but the cancer risk exceeded the threshold value (95th percentiles of total incremental lifetime cancer risk (TCR) was 8.91 × 10⁻⁵). Based on the results of uncertainty analysis, except for the exposure frequency, the total concentrations and DBF of As and Cr in <0.43 μm particle size segment have a greater influence on the uncertainty of probabilistic risk.

Estuarine rivers are the primary medium for transporting pollutants from human activities to the ocean. Polycyclic aromatic hydrocarbons (PAHs) have substantial toxicity and pose a significant risk to ecosystem and human health. However, the influences of urbanization on their distribution, particularly in China where urbanization is occurring rapidly, remain unclear. This study took three coastal economic circles of China as research areas, and investigated PAHs (16 species) in the estuarine river water. 95.9% of the sampling sites demonstrated moderate PAHs pollution and moderate ecological risk. Coal and petroleum combustion was the primary source of PAHs, but the source composition varied among the regions. Air pollution caused by energy emissions, particularly carbon emissions, has a critical and differential effect on PAHs distribution and deposition. With the increasing use of clean energy, PAHs emissions have been gradually reduced, which provides an effective option for PAHs reduction in a rapidly urbanizing coastal region.

Stable nitrogen isotope (δ¹⁵N) technology has often been used as a powerful tool to separate nitrogen oxides (NOₓ) produced by residential combustion (i.e., biomass burning and coal combustion) from other sources. However, the insufficient measurement of δ¹⁵N-NOₓ fingerprints of these emissions limits its application, especially in North China where residential emissions are significant. This study conducted combustion experiments to determine the δ¹⁵N-NOₓ of typical residential fuels in North China, including ten biomass fuels and five types of coal. The results showed that the δ¹⁵N of biomass varied between −6.9‰ and 2.3‰, which was lower than the δ¹⁵N of residential coal (−0.2‰–4.6‰). After combustion, the δ¹⁵N of biomass residues increased greatly, while that of coal residues showed no significant upward trend (p > 0.05). The δ¹⁵N-NOₓ produced by biomass burning ranged from −5.6‰ to 3.2‰ (−0.4‰ ± 2.4‰), showing a significant linear relation with δ¹⁵N-biomass. Comparatively, the δ¹⁵N-NOₓ derived from residential coal combustion was much higher (16.1‰ ± 3.3‰), ranging from 11.7‰ to 19.7‰. It was not well correlated with δ¹⁵N-coal, and only slightly lower than the estimated δ¹⁵N-NOₓ of industrial coal combustion (17.9‰, p > 0.05). These observations indicate that the δ¹⁵N-NOₓ of residential coal combustion is a result of the mixture of thermal- and fuel-released NOₓ. Based on the isotopic characteristics observed in this study, we analyzed the reported δ¹⁵N-NOₓ, and provided more statistically robust δ¹⁵N-NOₓ distributions for biomass burning (1.3‰ ± 4.3‰; n = 101) and coal combustion (17.9‰ ± 3.1‰; n = 26), which could provide guidance for scientific studies aiming to quantify the origin of NOₓ in North China and in other regions.

The most prominent source of Cu contamination in soils is metal mining and processing, partly since the Middle Age. However, coal mining and combustion can also cause (some) Cu contamination. We studied the distribution of Cu concentrations and isotope ratios in soils of the Huaibei coal mining area. The contribution of the coal mining and combustion to total Cu concentrations in soil was determined with a two-end-member mixing model based on the distinct δ⁶⁵Cu values of the Cu emitted from coal mining and combustion and in native soil. The mean Cu concentration of 75 mg kg⁻¹ exceeded the local soil background value (round to 22.13 mg kg⁻¹). The similar δ⁶⁵Cu value of grass near the coal mining and combustion operation as in gangue and flying ash indicated a superficial Cu contamination. Mining input was the dominant source of Cu in the contaminated soils, contributing up to 95% and on average 72% of the total Cu in the topsoils. The mining-derived Cu was leached to a depth of 65 cm, where still 29% of the Cu could be attributed to the mining emissions. Grasses showed lower δ⁶⁵Cu values than the topsoils, because of the preferential uptake of light Cu isotopes. However, the Δ⁶⁵Cugᵣₐₛₛ₋ₛₒᵢₗ was lower in the contaminated than the uncontaminated area because of superficial adsorption of isotopically heavy Cu from the mining emissions. Overall, in this study the distinct δ⁶⁵Cu values of the mining-derived Cu emissions and the native soil allowed for the quantification of the mining-derived Cu and had already reached the subsoil and contaminated the grass by superficial adsorption in only 60 years of mining operation.

To better promote environment friendly development of the coal chemical industry, this study investigated effects of methanol, sodium citrate, and chlorella powder (a type of microalgae) as co-metabolic substances on enhanced anaerobic treatment of coal pyrolysis wastewater with anaerobic sludge. The anaerobic sludge was loaded into four 2 L anaerobic reactors for co-metabolism enhanced anaerobic experiments. Anaerobic reactor 1 (R1) as control group did not add a co-metabolic substance; anaerobic reactor 2 (R2) added methanol; anaerobic reactor 3 (R3) added sodium citrate; and anaerobic reactor 4 (R4) added chlorella powder. In the blank control group, the removal ratios of total phenol (TPh), quinoline, and indole were only 12.07%, 42.15%, and 50.47%, respectively, indicating that 50 mg/L quinoline, 50 mg/L indole, and 600 mg/L TPh produced strong toxicity inhibition function on the anaerobic microorganism in reactor. When the concentration of methanol, sodium citrate, and chlorella was 400 μg/L, the reactors with co-metabolic substances had better treatment effect on TPh. Among them, the strengthening effects of sodium citrate (TPh removal ratio: 44.87%) and chlorella (47.85%) were better than that of methanol (38.72%) and the control group (10.62%). Additionally, the reactors with co-metabolic substances had higher degradation ratios on quinoline, indole, and chemical oxygen demand (COD). The data of extracellular polymeric substances showed that with the co-metabolic substances, anaerobic microorganisms produced more humic acids by degrading phenols and nitrogen-containing heterocyclic compounds (NHCs). Compared with the control group, the reactors added with sodium citrate and chlorella had larger average particle size of sludge. Thus, sodium citrate and chlorella could improve sludge sedimentation performance by increasing the sludge particle size. The bacterial community structures of reactors were explored and the results showed that Aminicenantes genera incertae sedis, Levinea, Geobacter, Smithella, Brachymonas, and Longilinea were the main functional bacteria in reactor added with chlorella.

Dust is regarded as an important pathway of heavy metal(loid)s to the human body. Health risks posed by metal(loid)s from household dust are of particular concern. However, the contamination and sources of heavy metal(loid)s in household dust environments, as well as source identification of health risks related to heavy metal(loid)s from household dust for vulnerable populations such as children, have not been thoroughly studied in China, particularly for the areas involved with industrial activities such as ore mining. Thus, a cross-sectional study was conducted in a rural area famous for Pb/Zn ore mining, to assess the pollution sources and health risks of heavy metal(loid)s from household indoor and outdoor dust and to identify the contribution of household dust to the health risks for children. The results indicated that household environment was heavily contaminated by metal(loid)s, which were mainly attributed to mining activity. Meanwhile, the indoor/outdoor ratio and the redundancy analysis indicated that there were other pollution sources in indoor environments such as coal combustion, materials for interior building and decoration. Vapor inhalation was the main exposure pathway for Hg, while ingestion was the predominant pathway for other metal(loid)s. Although the cancer risks were relatively low, the HIt from household indoor and outdoor dust (2.19) was about twice the acceptable limit (1) and was primarily from Pb (64.52%) and As (23.42%). Outdoor dust was a larger contributor to the HI of Sb, As, Cr, Cd, Zn and Pb, which accounted for 51.37%, 58.63%, 52.14%, 59.66%, 52.87% and 64.47%, respectively, and the HIt was mainly from outdoor dust (60.76%). These results indicated that non-cancer health risks were largely from outdoor dust exposure, and strengthened the notion that concern should be given to the potential health risks from metal(loid)s in household dust both originating from mining activity and indoor environmental sources.

Black carbon (BC) aerosol negatively affects air quality and contributes to climate warming globally. However, little is known about the relative contributions of different source control measures to BC reduction owing to the lack of powerful source-diagnostic tools. We combine the fingerprints of dual-carbon isotope using an optimized Bayesian Markov chain Monte Carlo (MCMC) scheme and for the first time to study the key sources of BC in megacity Guangzhou of the Pearl River Delta (PRD) region, China in 2018 autumn season. The MCMC model-derived source apportionment of BC shows that the dominant contributor is petroleum combustion (39%), followed by coal combustion (34%) and biomass burning (27%). It should be noted that the BC source pattern is highly sensitive to the variations of air masses transported with an enhanced contribution of fossil source from the eastern area, suggesting the important impact of regional atmospheric transportation on the BC source profile in the PRD region. Also, we further found that fossil fuel combustion BC contributed 84% to the total BC reduction during 2013–2018. The response of PM₂.₅ concentration to the ¹⁴C-derived BC source apportionment is successfully fitted (r = 0.90) and the results predicted that it would take ∼6 years to reach the WHO PM₂.₅ guideline value (10 μg m⁻³) for the PRD region if the emission control measures keep same as they are at present. Taken together, our findings suggest that dual-carbon isotope is a powerful tool in constraining the source apportionment of BC for the evaluations of air pollution control and carbon emission measures.

Many studies revealed the rapid decline of atmospheric PM₂.₅ in Beijing due to the emission control measures. The variation of particle number concentration (PN) which has important influences on regional climate and human health, however, was rarely reported. This study measured the particle number size distributions (PNSD) in 3–700 nm in winter of Beijing during 2013–2019. It was found that PN decreased by 58% from 2013 to 2017, but increased by 29% from 2017 to 2019. By Positive matrix factorization (PMF) analysis, five source factors of PNSD were identified as Nucleation, Fresh traffic, Aged traffic + Diesel, Coal + biomass burning and Secondary. Overall, factors associated with primary emissions were found to decrease continuously. Coal + biomass burning dominated the reduction (65%) among the three primary sources during 2013–2017, which resulted from the great efforts on emission control of coal combustion and biomass burning. Fresh traffic and Aged traffic + Diesel decreased by 43% and 66%, respectively, from 2013 to 2019, as a result of the upgrade of the vehicle emission standards in Beijing-Tianjin-Hebei area. On the other hand, the contribution from Nucleation and Secondary decreased with the reduction of gaseous precursors in 2013–2017, but due to the increased intensity of new particle formation (NPF) and secondary oxidation, they increased by 56% and 70%, respectively, from 2017 to 2019, which led to the simultaneously increase of PN and particle volume concentration. This study indicated that NPF may play an important role in urban atmosphere under continuous air quality improvement.