Radiocarbon-based impact assessment of open biomass burning on regional carbonaceous aerosols in North China

Isotopic comparison of ammonium between two summertime field campaigns in 2013 and 2021 at a background site of North China

Ammonia (NH3) is the primary atmospheric alkaline gas, playing a crucial role in the atmospheric chemistry. Recently, non-agricultural emissions have been identified as the dominant sources of NH3 in urban areas. However, few studies have quantified the contributions of different sources to regional NH3. This study conducted two summertime field observations in 2013 and 2021 at a background site of North China to comprehensively explore the regional variations in concentration, nitrogen isotope composition (δ15N), and sources of ammonium (NH4+). The results indicate that NHx (NHx = NH3 + NH4+) concentration has increased in 2021, but the fNH4+ (NH4+/ NHx) has decreased significantly. The δ15N-NH4+ values show a significant increase, ranging from -4.7 ± 8.1 ‰ to +12.0 ± 2.4 ‰. The increase can be attributed to two primary factors: changes in fNH4+ resulting from the reduction of atmospheric acid gases and alterations in the sources of NH3. Bayesian simulation analysis reveals substantial variations in NH3 sources between 2013 and 2021 observations. Non-agricultural sources have significantly increased their contribution to NHx concentration, with vehicle exhaust and NH3 slip experiencing growth rates of 187 % and 104 %, respectively. Our results confirm the dominate contribution of non-agricultural sources to regional NH3 at the present stage and propose relevant mitigation strategies, which would provide essential insights for reducing NH3 emissions in North China.

Health benefits from substituting raw biomass fuels for charcoal and briquette fuels: In vitro toxicity analysis

PM_2.5 (particulate matters with diameter ≤ 2.5 μm) from biomass fuel combustion has been identified as a major cause of cardiopulmonary diseases. Briquette and charcoal are two representative processed fuels that exhibit different emission characteristics. This study compared three types of biomass fuels (maize straw, wheat straw, and wood branches) and their respective processed fuels in terms of their emission factors (EFs). The bioreactivity of human alveolar epithelial (A549) cells to exposure to various fuel-emitted PM_2.5 was assessed. The EFs of lactic dehydrogenase (LDH) and interleukin-6 (IL-6) were calculated to compare actual cytotoxicity. The PM_2.5 EFs of maize and wheat straw were higher than those of wood branches, and following the processes of briquetting and carbonization, the EFs of PM_2.5 and chemical components were effectively reduced. Cell membrane damage and inflammatory responses were observed after A549 cell exposure to PM_2.5 extracts. The expression of bioreactivity to briquettes and charcoals was lower than that to raw fuels. The EFs of LDH and IL-6 were also significantly reduced after briquetting and carbonization. This underscores the necessity of fuel treatment for reducing cytotoxicity. The crucial chemical components that contributed to cell oxidative and inflammatory responses were identified, including organic and elemental carbon, water-soluble ions (e.g., K⁺, Mg²⁺, and Ca²⁺), metals (e.g., Fe, Cr, and Ni), and high-molecular-weight PAHs. This study elucidated the similarities and differences of PM_2.5 emissions and cytotoxicity of three types of biomass fuel and demonstrated the positive effects of fuel treatment on reducing adverse pulmonary effects.

Characterization of carbonaceous substances emitted from residential solid fuel combustion using real-world data from the Beijing-Tianjin-Hebei region

Residential solid fuel emissions are among the most important sources of carbonaceous substances that exert harmful effects on air quality, human health and climate change. Considering the constantly updated emission reduction policies for residential solid fuel combustion in the Beijing-Tianjin-Hebei (BTH) region, the emission data for the source should updated in a timely manner. Testing was performed on residential solid fuel emissions in the BTH region, China. The emission factors and profiles of carbonaceous substances (including organic carbon (OC), elemental carbon (EC), EPA priority polycyclic aromatic hydrocarbons (EPAHs), methyl PAHs (MPAHs), and n-alkanes) emitted from residential solid fuels were obtained. The results showed the ranges of emission factors of PM_2.5, OC, EC, EPAHs, MPAHs and n-alkanes from residential solid fuel emissions were 1.92-17.6, 0.312-6.85, 0.066-2.33, 0.004-0.58, 0.003-0.87 and 0.009-0.39 g/kg fuel, respectively. The carbon fraction profiles showed that OC1, OC2, and EC1 were the major products of residential solid fuel combustion, and the non-polar organic matter profiles showed that Fluo and MFluo were dominant. The effects of combustion modes, types of stove and types of the fuel on emission characteristics of carbonaceous substances were discussed in detail. The emission factors of carbonaceous substances from the smoldering phase and traditional stove were higher than those from the flaming phase and improved stove, respectively, which was mainly controlled by the modified combustion efficiency (MCE). It was found that the emission factors of pollutants with decreasing MCE values sharply increased, especially when the MCE values were below 90%. Finally, some diagnostic ratios were discussed, and it was determined that residential coal combustion is considered to occur at MPAHs/PAHs higher than 1.5 and MFluo/Fluo higher than 5.

Refined source apportionment of residential and industrial fuel combustion in the Beijing based on real-world source profiles

Residential and industrial emissions are considered as dominant contributors to ambient fine particulate matter (PM_2.5) in China. However, the contributions of residential and industrial fuel combustion are difficult to distinguish because specific source indicators are lacking. In this study, real-world source testing was performed on residential coal, biomass and industrial combustion, industrial processes, and diesel and gasoline vehicle source emissions in the Beijing-Tianjin-Hebei region, China. PM_2.5 emission factors and chemical profiles, including 97 compositions (e.g., carbonaceous matter, water-soluble ions, elements, EPA priority polycyclic aromatic hydrocarbons (EPAHs), methyl PAHs (MPAHs), and n-alkanes) were obtained for the aforementioned sources. The results showed high OC1, OC2, fluoranthene, methyl fluoranthene, and retene in emissions from residential coal combustion, high OC3, sulfate, Ca, and iron abundance in emissions from industrial combustion, and high Pb and Zn loadings in emissions from industrial processes. Furthermore, specific diagnostic ratios were determined to distinguish between residential and industrial fuel combustion. For example, the ratios of MPAHs/EPAHs (>1) and Mfluo/Fluo (>5) can be used as fingerprinting ratios to distinguish residential coal combustion from other sources. Finally, 1-h resolution refined source apportionments of PM_2.5 were conducted in Beijing during two haze events (EP1 and EP2) with a chemical mass balance (CMB) model based on the localized real-world source profiles established in this study. Source apportionment results of CMB showed that the contributions of industrial and residential fuel combustion were 19.4% and 30.8% in EP1 and 26.8% and 18.1% in EP2, respectively, which were comparable to the results of the positive matrix factorization model (R² = 0.82). This study provides valuable information for the successful and accurate determination of the contributions of residential and industrial fuel combustion to ambient PM_2.5.

In-vitro oxidative potential and inflammatory response of ambient PM2.5 in a rural region of Northwest China: Association with chemical compositions and source contribution

Overproduction of reactive oxygen species (ROS) induced by atmospheric particles and subsequent inflammatory responses are considered as one of the most important pathological mechanisms with regard to the adverse effects of air pollution exposure. In this study, fine particulate matter (PM_2.5) samples were collected at a rural site in Guanzhong Basin, Northwest China, in both summer (August 3-23, 2016) and winter (January 5-February 1, 2017). Then, human bronchial epithelial BEAS-2B cells were exposed to the PM_2.5, cultured for 24 h, and then assayed for particle-induced ROS and three inflammatory factors (tumor necrosis-α (TNF-α), interleukin-6 (IL-6), and interferon-γ (IFN-γ)) in vitro. The oxidative potential (OP) induced by winter PM_2.5 samples was higher than that induced by summertime samples, whereas inflammatory values showed contrasting seasonal variations. Both OP and inflammatory factors were significantly correlated with most chemical compounds in winter, but not in summer, which was thought to be related mainly to the higher contribution from secondary aerosols formed during the warm season. Source apportionment results showed secondary aerosols formation have significant contribution to OP of PM_2.5 in both seasons, but the dominant oxidation processes is different. Secondary nitrates-related process was the major contributors regulating the OP in winter; however, secondary sulfates formation were mainly responsible for the ROS responses in summer. For primary emission, biomass burning, rather than coal emission or vehicle exhaust, was the significant source for OP of PM_2.5 in winter. In most cases, the source contribution of each inflammatory factor was similar to that of the ROS. Our results highlighted the significant health risk of atmospheric aerosols from biomass burning in the rural regions of Guanzhong Basin, Northwest China.

Radiocarbon in the atmospheric gases and PM10 aerosol around the Paks Nuclear Power Plant, Hungary

Our study shows a one-year-long, monthly integrated continuous monitoring campaign of gaseous radiocarbon emission and ambient air compared with 4 event-like, weekly (168 h) atmospheric aerosol radiocarbon data in every season of 2019, at 4 locations (n = 16 aerosol sample) around the Paks Nuclear Power Plant, Hungary. The study shows the first aerosol radiocarbon results around a nuclear power plant measured by accelerator mass spectrometry in Hungary. There was no dominant contribution detected in the atmospheric CO₂ gas fraction, but we could detect excess radiocarbon in the total gaseous carbon fraction at almost every sampling point around the Paks Nuclear Power Plant. The highest Δ¹⁴C value in the total gaseous carbon form was 157.9 ± 4.6‰ in November and the highest Δ ¹⁴C value in the CO₂ fraction was 86.1 ± 4.0‰ in December during 2019. Observed ¹⁴C activity excess is not higher than previously published values around the Paks Nuclear Power plant at the same sampling points (Molnár et al., 2007; Varga et al., 2020). Our aerosol radiocarbon measurements show that there is no significant contribution from the nuclear power plant to the atmospheric PM₁₀ fraction. We could not detect a Δ ¹⁴C value higher than 0‰ in any season. The results show that the simple aerosol sampling, without pre-treatment of the filters, is appropriate for the measurement of excess radiocarbon at the vicinity of nuclear power plants. The applied preparation and measurement method can be applicable for detection of hot (¹⁴C) particles and early identification of radiocarbon emission from nuclear power plants in the PM₁₀ fraction.

Approval Research for Carcinogen Humic-Like Substances (HULIS) Emitted from Residential Coal Combustion in High Lung Cancer Incidence Areas of China

The incidence and mortality rate of lung cancer is the highest in Xuanwei County, Yunnan Province, China. The mechanisms of the high lung incidence remain unclear, necessitating further study. However, the particle size distribution characteristics of HULIS emitted from residential coal combustion (RCC) have not been studied in Xuanwei. In this study, six kinds of residential coal were collected. Size-resolved particles emitted from the coal were sampled by using a burning system, which was simulated according to RCC made in our laboratory. Organic carbon (OC), elemental carbon (EC), water-soluble inorganic ion, water-soluble potentially toxic metals (WSPTMs), water-soluble organic carbon (WSOC), and HULIS-C (referred to as HULIS containing carbon contents) in the different size-segregated particulate matter (PM) samples were determined for health risk assessments by inhalation of PM. In our study, the ratio of HULIS-Cx to WSOCx values in RCC particles were 32.73–63.76% (average 53.85 ± 12.12%) for PM2.0 and 33.91–82.67% (average 57.06 ± 17.32%) for PM2.0~7.0, respectively. The carcinogenic risks of WSPTMs for both children and adults exceeded the acceptable level (1 × 10−6, indicating that we should pay more attention to these WSPTMs). Exploring the HULIS content and particle size distribution of the particulate matter produced by household coal combustion provides a new perspective and evidence for revealing the high incidence of lung cancer in Xuanwei, China.

Reapportioning the sources of secondary components of PM2.5: A combined application of positive matrix factorization and isotopic evidence

Secondary particles account for a considerable proportion of fine particles (PM_2.5) and reasonable reapportioning them to primary sources is critical for designing effective strategies for air quality improvement. This study developed a method which can reapportion secondary sources of PM_2.5 solved by positive matrix factorization (PMF) to primary sources based on the isotopic signals of nitrate, ammonium and sulfate. Actual PM_2.5 data in Beijing were used as a case study to assess the feasibility and capacity of this method. In the case, 20 chemical components were used to apportion PM_2.5 sources and source contributions of nitrate were applied to reapportion secondary source to primary sources. The model performance was also estimated by radiocarbon measurement (¹⁴C) of organic (OC) and elemental (EC) carbons of eight samples. The PMF apportioned seven sources: the secondary source (36.1%), vehicle exhausts (18.7%), industrial sources (13.6%), biomass burning (11.4%), coal combustion (8.10%), construction dust (7.93%) and fuel oil combustion (4.24%). After the reapportionment of the secondary source, vehicle exhausts (28.7%) contributed the most to PM_2.5, followed by biomass burning (25.1%) and industrial sources (18.9%). Fossil oil combustion and coal combustion increased to 8.00% and 11.4%, respectively, and construction dust contributed the least. The average gap between contributions of identified sources to OC and EC and the ¹⁴C measurements decreased 2.5 ± 1.2% after the reapportionment than 13.2 ± 10.8%, indicating the good performance of the developed method.

Molecular characteristics of organic compositions in fresh and aged biomass burning aerosols

Biomass burning (BB) is the most important source of primary organic aerosols (OA) in the atmosphere that has significant impact on local/regional air quality and human health. However, few studies paid attention to the evolution of molecular characteristics of BB OA in the atmospheric aging processes. In this study, both fresh and aged PM_2.5 aerosols from burning of rice, maize, and wheat straws were collected from a combined system of combustion chamber and oxidation flow reactor, and were analyzed for >100 organic species. The emission factors (EFs) of anhydrosugars and some fatty acids showed slight variations between fresh and aged samples, indicating that these compounds are relatively stable. However, the EFs of n-alkanes, fatty alcohols, and parent-PAHs decreased 8-57% from fresh to aged samples, suggesting that they can undergo further oxidation to form other organic materials in the atmosphere. Phthalic acids, nitrophenols and isoprene-derived products were mainly secondarily formed by aging processes. Thus their EFs increased by 2-23 times from fresh to aged samples. Levoglucosan was the most abundant individual organic tracer, and its EF varied slightly between fresh and aged samples, proving its indicative role on BB emission. Moreover, the ratio of vanillic acid to levoglucosan and p-hydroxybenzoic acid to levoglucosan increased 2-13 times from fresh to aged samples. Therefore they can be used to investigate the impact of aging processes on BB aerosols in the atmosphere. RO₂ + HO₂ pathway derived 2-methyltetrols (2-MTs) predominated the EFs of isoprene-derived products (SOA_i) in the fresh samples. However, RO₂ + NO pathway derived 2-methylglyceric acid (2-MGA) increased by >30 times and became comparable with 2-MTs in aged particles. The ratio of 2-MGA/2-MTs increased from 0.06-0.27 in fresh samples to 0.94-1.18 in aged samples, because the high loading of NO_x in BB smoke enhanced the formation of SOA_i through RO₂ + NO reactions.

Spatial variability of sedimentary carbon in South Yellow Sea, China: impact of anthropogenic emission and long-range transportation

During the last few decades, sedimentary carbons gain great concerns of research interest among the scientific committee worldwide due to their adverse impact on aquatic chemistry, ecology, and hence human health along with global climate change. In the present study, we investigated the spatial distribution of mass concentration of sedimentary carbon (viz. black carbon: BC, and its components, char and soot) along with their burial fluxes in the surface sediments of the South Yellow Sea (SYS). The concentration of sedimentary carbon is measured by using an emerging method of thermal/optical reflectance. The observed BC concentration is found in the range of 0.02-1.02 mg g^-1 with a mean value of 0.49 ± 0.26 mg g^-1. The mean burial fluxes of BC, char, and soot also have a similar spatial variation to their concentration with the mean value along with relative standard deviation (in bracket) 22.43 ± 12.49 (~ 56%), 5.90 ± 3.99 (~ 68%), and 16.53 ± 10.67 (65%), respectively. Relatively lower value of char/soot ratio, i.e., 0.48 ± 0.22, indicates the dominance of soot in surface sediments that could be mainly derived from the fossil fuel combustion which is further confirmed from emission inventory data suggesting maximum contribution, i.e., ~ 66-80%, of the total BC emission emitted from residential and industrial emission sources. The back trajectories analysis revealed a significant impact of long-range transportation on BC concentration in the surface sediments of SYS. Further study of BC concentrations in sea sediments and their interaction with other organic/inorganic compounds in continental shelves is highly needed for a better understanding of the global carbon cycle.

Source Apportionment of PM2.5 in Guangzhou Based on an Approach of Combining Positive Matrix Factorization with the Bayesian Mixing Model and Radiocarbon

To accurately apportion the sources of aerosols, a combined method of positive matrix factorization (PMF) and the Bayesian mixing model was applied in this study. The PMF model was conducted to identify the sources of PM2.5 in Guangzhou. The secondary inorganic aerosol source was one of the seven main sources in Guangzhou. Based on stable isotopes of oxygen and nitrogen (δ15N-NO3− and δ18O-NO3−), the Bayesian mixing model was performed to apportion the source of NO3− to coal combustion, traffic emission and biogenic source. Then the secondary aerosol source was subdivided into three sources according to the discrepancy in source apportionment of NO3− between PMF and Bayesian mixing model results. After secondary aerosol assignment, the six main sources of PM2.5 were traffic emission (30.6%), biomass burning (23.1%), coal combustion (17.7%), ship emission (14.0%), biomass boiler (9.9%) and industrial emission (4.7%). To assess the source apportionment results, fossil/non-fossil source contributions to organic carbon (OC) and element carbon (EC) inferred from 14C measurements were compared with the corresponding results in the PMF model. The results showed that source distributions of EC matched well between those two methods, indicating that the PMF model captured the primary sources well. Probably because of the lack of organic molecular markers to identify the biogenic source of OC, the non-fossil source contribution to OC in PMF results was obviously lower than 14C results. Thus, an indicative organic molecular tracer should be used to identify the biogenic source when accurately apportioning the sources of aerosols, especially in the region with high plant coverage or intense biomass burning.

Dual-modelling-based source apportionment of NOx in five Chinese megacities: Providing the isotopic footprint from 2013 to 2014

In China, nitrate (NO₃^-) becomes the main contributor to fine particles (PM_2.5) because the emissions of its precursor, nitrogen oxides (NO_x), were not recognized and controlled well in recent years. In this work, sources, conversion, and geographical origin of NO_x were interpreted combining the isotopic information (δ¹⁵N and δ¹⁸O) of NO₃^- and dual modelling at five Chinese megacities (Beijing, Shanghai, Guangzhou, Wuhan and Chengdu) during 2013-2014. Results showed that the δ¹⁵N-NO₃^- values (n = 512) ranged from -12.3‰ to +22.9‰, and the average δ¹⁸O-NO₃^- value was +83.4‰ ± 17.2‰. The isotopic compositions both had a rising tendency as ambient temperature dropped, attributing largely to the source changes. Bayesian model indicated the percentage for the OH pathway of NO_x conversion had a clear seasonal variation with a higher value during summer (58.0% ± 9.82%) and a lower value during winter (11.1% ± 3.99%); it was also significantly correlated with latitude (p < 0.01). Coal combustion was the most important source of NO_x (31.1%-41.0%), which was geographically derived from North China and other south-central developed regions implied by Potential Source Contribution Function (PSCF). Apart from Chengdu, mobile sources was the second largest contributor to NO_x. This source was extensive but uniformly distributed all around the typical urban agglomerations of China. Biomass burning and microbial processes shared similar source areas, mostly originating from the North China Plain and Sichuan Basin. Based on the NO_x features, we infer that residential coal combustion was the primary source of heavy PM_2.5 pollution in Chinese megacities. Controlling the source categories of these regional priorities would help mitigate atmospheric pollution in these areas.

Occurrence, source, and risk assessment of atmospheric parent polycyclic aromatic hydrocarbons in the coastal cities of the Bohai and Yellow Seas, China

Parent polycyclic aromatic hydrocarbons (PPAHs) in the ambient air of the coastal cities near the Bohai and Yellow Seas were measured over a full year. The range and geometric average of total PPAH₂₉ (29 species) were 5.16-1.22 × 10³ and 118 ng/m³, respectively, with 77 ± 14% in a gaseous phase. The 16 priority components accounted for 90 ± 4% of the total mass concentration. The incremental life cancer risk (ILCR) via inhalation exposure to the PPAHs (3.17 × 10^-4) was underestimated by 80%, as only the priority PPAHs were considered. The air concentrations of PPAHs in the Bohai Sea area were generally higher (p < 0.01) than those in the Yellow Sea area. A significant increase (p < 0.01) in the levels of PPAHs and large fractions of high molecular weight (HMW) components were observed in winter. Absorption by particulate organic carbon dominated in gas-particle partitioning of the PPAHs, and the seasonal variations in gas-particle partitioning of the low and moderate molecular weight compounds were more noticeable relative to the HMW species. In summer, significantly higher concentrations of PPAHs were found in the daytime than during nighttime, while the opposite case occurred in winter (p < 0.05). The positive matrix factorization (PMF) results indicated greater contributions of coal and biomass combustion to the PPAH emissions in the coastal cities of the Bohai Sea area compared with the Yellow Sea area. The burning of coal and biomass served as the main source of PPAHs in winter, while traffic exhaust was the dominant source in other seasons. The potential source contribution function (PSCF) revealed the important impacts of the external inputs on the local PPAHs via air mass transport. The contributions of the resolved emission sources to the ILCR were clearly different from those of the mass concentrations, indicating the necessity for source-oriented risk assessments.

Way forward for straw burning pollution research: a bibliometric analysis during 1972-2016

Straw burning has become a hot topic in recent years as it poses a great risk not only to the lung health of residents in exposed areas but also to large-scale haze events. In order to have a more comprehensive understanding of straw burning research, based on the bibliometric analysis of Science Citation Index Expanded from Web of Science, the research progress of straw burning pollution from 1972 to 2016 and the future research trends were carried out in this paper. The research focuses on the document type, language, publication year, times cited and its output characteristics, subject category, journal, national and institutional distribution, author, etc. The results show that the study of straw burning pollution has shown a significant increase over the past 45 years. A total of 813 publications were found, and English was the most commonly used language. Articles were the most frequently appeared document types, and the researches were strongly embracing with the top 3 popular subject categories of "environmental sciences and ecology," "agriculture," and "meteorology and atmospheric sciences." We identified that the major journals publishing straw burning pollution research were Atmospheric Environment, followed by Atmospheric Chemistry and Physics. China as a leader in paper quantity played an important role in the research field of straw burning pollution, while the USA and India were located in the second and third positions. The most productive institution was Chinese Academy of Sciences, followed by Peking University and University Arkansas. Based on our analysis and the consideration of current environmental problems, more studies should focus on the following three aspects in the future: driving mechanism of emission characteristics, construction of high-resolution emission inventories, and the influencing mechanism of straw burning pollutants on climate change and human health. Our analysis and prospects can be served as a useful reference for future studies.

The contribution of atmospheric particulate matter to the formation of CX3R-type disinfection by-products in rainwater during chlorination

Atmospheric particulate matter (PM) can be scavenged by rainfall and contribute dissolved organic matter (DOM) to rainwater. Rainwater may serve as a part or the whole of drinking water sources, leading to the introduction of PM-derived DOM into drinking water. However, little information is available on the role of PM-derived DOM as a remarkable precursor of CX₃R-type disinfection by-products (DBPs) in rainwater. In this study, samples were collected from ten occurrences of rainfall in Shanghai and batch experiments were executed to explore the contribution of PM-derived DOM to CX₃R-type DBP formation in rainwater and to further understand some of unknowns regarding its characteristics. Results revealed that a part of PM was scavenged by rainfall and the scavenge performance was better for smaller PM. The formation potentials (FPs) of individual CX₃R-type DBP were similar among size-isolated PM. TCM was predominant (around 0.5-4.5 μg-C/mg-C) and TCAA was the secondary (around 0.6-3.2 μg-C/mg-C) among all detectable CX₃R-type DBPs. Based on the PM removal data and DBP FP results, the contribution of PM-derived DOM to CX₃R-type DBP formation in rainwater was modeled. Furthermore, aromatic proteins and soluble microbial product-like compounds were found to be significant compositions, which were reported to be DBP precursors. And low molecular weight (< 10 kDa) DOM derived from total PM and rainwater exhibited higher CX₃R-type DBP FPs. DOM fractions with higher SUVA₂₅₄ and SUVA₂₈₅ values gave relatively higher yields of CX₃R-type DBPs, indicating that aromatic compounds played an important role in DBP formation.

Assessment and quantification of NOx sources at a regional background site in North China: Comparative results from a Bayesian isotopic mixing model and a positive matrix factorization model

Regional sources of nitrogen oxides (NO_x) in North China during summer were explored using both a Bayesian isotopic mixing model and a positive matrix factorization (PMF) model. Results showed that the nitrogen isotope (δ¹⁵N) composition of particulate nitrate (NO₃^-) varied between -8.9‰ and +14.1‰, while the oxygen isotope (δ¹⁸O) composition ranged from +57.4‰ to +93.8‰. Based on results from the Bayesian isotopic mixing model, the contribution of the hydroxyl radical (•OH) NO_x conversion pathway showed clear diurnal fluctuation; values were higher during the day (0.53 ± 0.16) and lower overnight (0.42 ± 0.17). Values peaked at 06:00-12:00 and then decreased gradually until 00:00-06:00 the next day. Coal combustion (31.34 ± 9.04%) was the most significant source of NO_x followed by biomass burning (25.74 ± 2.58%), mobile sources (23.83 ± 3.66%), and microbial processes (19.09 ± 5.21%). PMF results indicated that the contribution from mobile sources was 19.83%, slightly lower as compared to the Bayesian model (23.83%). The PMF model also reported a lower contribution from coal combustion (28.65%) as compared to the Bayesian model (31.34%); however, the sum of biomass burning and microbial processes in the Bayesian model (44.83%) was lower than the aggregate of secondary inorganic aerosol, sea salt, and soil dust in PMF model (51.52%). Overall, differences between the two models were minor, suggesting that this study provided a reasonable source quantification for NO_x in North China during summer.

Oxidative potential of ambient PM2.5 in the coastal cities of the Bohai Sea, northern China: Seasonal variation and source apportionment

Emissions of air pollutants from primary and secondary sources in China are considerably higher than those in developed countries, and exposure to air pollution is main risk of public health. Identifying specific particulate matter (PM) compositions and sources are essential for policy makers to propose effective control measures for pollutant emissions. Ambient PM_2.5 samples covered a whole year were collected from three coastal cities of the Bohai Sea. Oxidative potential (OP) was selected as the indicator to characterize associated PM compositions and sources most responsible for adverse impacts on human health. Positive matrix factorization (PMF) and multiple linear regression (MLR) were employed to estimate correlations of PM_2.5 sources with OP. The volume- and mass-based dithiothreitol (DTT_v and DTT_m) activities of PM_2.5 were significantly higher in local winter or autumn (p < 0.01). Spatial and seasonal variations in DTT_v and DTT_m were much larger than mass concentrations of PM_2.5, indicated specific chemical components are responsible for PM_2.5 derived OP. Strong correlations (r > 0.700, p < 0.01) were found between DTT activity and water-soluble organic carbon (WSOC) and some transition metals. Using PMF, source fractions of PM_2.5 were resolved as secondary source, traffic source, biomass burning, sea spray and urban dust, industry, coal combustion, and mineral dust. Further quantified by MLR, coal combustion, biomass burning, secondary sources, industry, and traffic source were dominant contributors to the water-soluble DTT_v activity. Our results also suggested large differences in seasonal contributions of different sources to DTT_v variability. A higher contribution of DTT_v was derived from coal combustion during the local heating period. Secondary sources exhibited a greater fraction of DTT_v in summer, when there was stronger solar radiation. Traffic sources exhibited a prevailing contribution in summer, and industry contributed larger proportions in spring and winter. Future abatement priority of air pollution should reduce the sources contributing to OP of PM_2.5.

Assessing on toxic potency of PM2.5-bound polycyclic aromatic hydrocarbons at a national atmospheric background site in North China

A total of 76PM_2.5 samples collected at Tuoji Island from November 2011 to January 2013 were used to analyze 15 congeners of polycyclic aromatic hydrocarbons (∑₁₅PAHs) and assess their toxic potency. The average ∑₁₅PAHs was 15.34±8.87ngm^-3, ranging from 4.24 to 40.62ngm^-3 over the sampling period. BkF, BbF, Phe and BaP were dominant PAH congeners, contributing together 60.64% of the ∑₁₅PAH concentration. The highest monthly ∑₁₅PAHs concentration was in January 2012, followed by the next January, which was closely four times greater than the lowest level occurred in July 2012. Wheat straw burning was responsible for the high PAH concentrations in June 2012. The averaged BaP toxicity equivalent (TEQ-BaP) concentration was 2.70±1.88ngm^-3 over the sampling period. BaP and DaA were the largest contributors, which contributed 58.5% and 14.7% of totals, respectively. The high TEQ-BaP and TEQ-BaP value per unit of ∑₁₅PAHs concentration (TEQ-BaP(U)) values occurred in the cold season and the low levels presented in the warm period. The heaviest monthly TEQ-BaP was 5.28±2.84ngm^-3, which appeared in January 2012; the lowest value was 0.86±0.33ngm^-3, which occurred in July 2012. The potential source contribution function (PSCF) showed the occurrence of the high health risk associated with PAHs in the middle of Liaoning and the south of Shandong Peninsula.

Cell death pathways of particulate matter toxicity

Humans are exposed to various complex mixtures of particulate matter (PM) from different sources. Long-term exposure to high levels of these particulates has been linked to a diverse range of respiratory and cardiovascular diseases that have resulted in hospital admission. The evaluation of the effects of PM exposure on the mechanisms related to cell death has been a challenge for many researchers. Therefore, in this review, we have discussed the effects of airborne PM exposure on mechanisms related to cell death. For this purpose, we have compiled literature data on PM sources, the effects of exposure, and the assays and models used for evaluation, in order to establish comparisons between various studies. The analysis of this collected data suggested divergent responses to PM exposure that resulted in different cell death types (apoptosis, autophagy, and necrosis). In addition, PM induced oxidative stress within cells, which appeared to be an important factor in the determination of cell fate. When the levels of reactive oxygen species were overpowering, the cellular fate was directed toward cell death. This may be the underlying mechanism of the development or exacerbation of respiratory diseases, such as emphysema and chronic obstructive pulmonary diseases. In addition, PM was shown to cause DNA damage and the resulting mutations increased the risk of cancer. Furthermore, several conditions should be considered in the assessment of cell death in PM-exposed models, including the cell culture line, PM composition, and the interaction of the different cells types in in vivo models.

Combining Positive Matrix Factorization and Radiocarbon Measurements for Source Apportionment of PM2.5 from a National Background Site in North China

To explore the utility of combining positive matrix factorization (PMF) with radiocarbon (¹⁴C) measurements for source apportionment, we applied PM_2.5 data collected for 14 months at a national background station in North China to PMF models. The solutions were compared to ¹⁴C results of four seasonally averaged samples and three outlier samples. Comparing the most readily interpretable PMF solutions and ¹⁴C results revealed that PMF modeling was well able to capture the source patterns of PM_2.5 with two and three irrelevant source classifications for the seasonal and outlier samples. The contribution of sources that could not be classified as either fossil or non-fossil sources in the PMF solution, and the errors between the modeled and measured concentrations weakened the effectiveness of the comparison. Based on these two factors, we developed an index for selecting the most suitable ¹⁴C measurement samples for combining with the PMF model. Then we examined the potential for coupling PMF modeling and ¹⁴C data with a constrained PMF run using the ¹⁴C data as a priori information. The restricted run could provide a more reliable solution; however, the PMF model must provide a flexible dialog to input the priori restrictions for executing the constraint simulation.

Source apportionment of sediment organic material in a semi-enclosed sea using Bayesian isotopic mixing model

To determine sources of organic material in semi-enclosed Bohai Sea, samples of marine surface sediments, suspended particulates in adjacent rivers and atmospheric deposition were collected and analyzed for grain size composition, total organic carbon(TOC and POC), total nitrogen (TN and PN), and stable isotopic composition (δ¹³C and δ¹⁵N). Measured bulk C/N ratio (5.50-12.28), δ¹³C (-23.59~-19.54‰), and δ¹⁵N (2.80-8.07‰) values of surface sediment organic materials indicated a mixed source of marine and terrestrial contributions. Spatial distribution of organic C, N and their stable isotope composition indicated a land-sea gradient of organic material content and source combination. Using MixMIR model with dual isotopes, it was estimated that relative contributions of marine, riverine, and atmospheric sources to sediment mixture were 69.0%, 9.6%, and 21.4%, respectively. Our results demonstrated the advantage of Bayesian isotope mixing models over the conventional end-member mixing models for source apportionment in coastal seas with complex source origins.

First Assessment of NOx Sources at a Regional Background Site in North China Using Isotopic Analysis Linked with Modeling

Nitrogen oxides (NO_x, including NO and NO₂) play an important role in the formation of atmospheric particles. Thus, NO_x emission reduction is critical for improving air quality, especially in severely air-polluted regions (e.g., North China). In this study, the source of NO_x was investigated by the isotopic composition (δ¹⁵N) of particulate nitrate (p-NO₃^-) at Beihuangcheng Island (BH), a regional background site in North China. It was found that the δ¹⁵N-NO₃^- (n = 120) values varied between -1.7‰ and +24.0‰ and the δ¹⁸O-NO₃^- values ranged from 49.4‰ to 103.9‰. On the basis of the Bayesian mixing model, 27.78 ± 8.89%, 36.53 ± 6.66%, 22.01 ± 6.92%, and 13.68 ± 3.16% of annual NO_x could be attributed to biomass burning, coal combustion, mobile sources, and biogenic soil emissions, respectively. Seasonally, the four sources were similar in spring and fall. Biogenic soil emissions were augmented in summer in association with the hot and rainy weather. Coal combustion increased significantly in winter with other sources showing an obvious decline. This study confirmed that isotope-modeling by δ¹⁵N-NO₃^- is a promising tool for partitioning NO_x sources and provides guidance to policymakers with regard to options for NO_x reduction in North China.

Comparison of inorganic chemical compositions of atmospheric TSP, PM10 and PM2.5 in northern and southern Chinese coastal cities

To compare the inorganic chemical compositions of TSP (total suspended particulate), PM₁₀ (particulate matter with an aerodynamic diameter less than 10μm) and PM_2.5 (particulate matter with an aerodynamic diameter less than 2.5μm) in southern and northern cities in China, atmospheric particles were synchronously collected in Dalian (the northern city) and Xiamen (the southern city) in spring and autumn of 2004. The mass concentrations, twenty-three elements and nine soluble ions were assessed. The results show that in Dalian, the mass concentrations of Mg, Al, Ca, Mn and Fe in spring were 4.0-10.1, 2.6-8.0, 4.1-12, 1.2-3.6 and 2.9-7.9 times higher, respectively, than those in Xiamen. The dust storm influence is more obvious in Dalian in spring. However, in Xiamen, heavy metals accounted for 13.9%-17.9% of TSP, while heavy metals contributed to 5.5%-9.3% of TSP in Dalian. These concentrations suggest that heavy metal pollution in Xiamen was more serious. In addition, the concentrations of Na⁺, Cl^-, Ca²⁺ and Mg²⁺ were higher in Dalian due to the influence of marine aerosol, construction activities and soil dust. The NO^3-/SO₄^2- ratios in Dalian (0.25-0.49) were lower than those in Xiamen (0.51-0.62), indicating that the contributions of vehicle emission to particles in Xiamen were higher. Coefficient of divergence values was higher than 0.40, implying that the inorganic chemical composition profiles for the particles of Dalian and Xiamen were quite different from each other.

A review of biomass burning: Emissions and impacts on air quality, health and climate in China

Biomass burning (BB) is a significant air pollution source, with global, regional and local impacts on air quality, public health and climate. Worldwide an extensive range of studies has been conducted on almost all the aspects of BB, including its specific types, on quantification of emissions and on assessing its various impacts. China is one of the countries where the significance of BB has been recognized, and a lot of research efforts devoted to investigate it, however, so far no systematic reviews were conducted to synthesize the information which has been emerging. Therefore the aim of this work was to comprehensively review most of the studies published on this topic in China, including literature concerning field measurements, laboratory studies and the impacts of BB indoors and outdoors in China. In addition, this review provides insights into the role of wildfire and anthropogenic BB on air quality and health globally. Further, we attempted to provide a basis for formulation of policies and regulations by policy makers in China.

Chemical composition of PM2.5 from two tunnels with different vehicular fleet characteristics

The chemical compositions of PM2.5 including OC, EC, water soluble ions, elements, and organic components such as polycyclic aromatic hydrocarbons (PAHs), hopanes, and steranes, emitted in Wuzushan (WZS) and Kuixinglou (KXL) tunnels were determined. WZS tunnel is a major route for diesel vehicles traveling, while KXL tunnel has limited to diesel vehicles. The results showed that the proportions of the different constituents of PM2.5 in the Wuzushan (WZS) tunnel were OC (27.7%), EC (32.1%), elements (13.9%), and water soluble ions (9.2%). Whereas the chemical profile of PM2.5 in the Kuixinglou (KXL) tunnel was OC (17.7%), EC (10.4%), elements (8.90%), and water soluble ions (8.87%). The emission factors (EFs) of PM2.5 and proportions of SO4(2-) and Pb were decreased by vehicle emission standards and fuel quality policy in China, and the higher molecular weight PAHs (4+5+6 rings) were more abundant than the lower molecular weight PAHs (2+3 rings) in the two tunnels. The proportions of 17A(H)-21B(H)-30-Norhopane and 17A(H)-21B(H)-Hopane in the hopane and sterane were not dependent on the vehicles types. In addition, specific composition profiles for PM2.5 from gasoline-fueled vehicles (GV) and diesel-fueled vehicles (DV) emissions were drafted, which indicated that OC (0.974mg·veh(-1)·km(-1)) was the most abundant component in PM2.5, followed by Fe, Cl(-), and Mg for GV. The relative proportions of the different constituents in the PM2.5 for DV were EC (35.9%), OC (27.2%), elements (12.8%), and water soluble ions (11.7%). Both the PM2.5 EFs and EC proportions in DV were higher than those in GV, and the HMW PAHs were the dominant PAHs for both GV and DV. The PM2.5 emissions from the vehicles in Yantai were 581±513tons to 1353±1197tons for GV, and 19,627±2477tons to 23,042±2887tons for DV, respectively.