Source Apportionment of Fine-Particle, Water-Soluble Organic Nitrogen and Its Association with the Inflammatory Potential of Lung Epithelial Cells

Ambient PM2.5 and specific sources increase inflammatory cytokine responses to stimulators and reduce sensitivity to inhibitors

Ambient exposure to fine particulate matter (PM2.5) is associated with increased morbidity and mortality from multiple diseases. Recent observations suggest the hypothesis that trained immunity contributes to these risks, by demonstrating that ambient PM2.5 sensitizes innate immune cells to mount larger inflammatory response to subsequent bacterial stimuli. However, little is known about how general and durable this sensitization phenomenon is, and whether specific sources of PM2.5 are responsible. Here we consider these issues in a longitudinal study of children. The sample consisted of 277 children (mean age 13.92 years; 63.8% female; 38.4% Black; 32.2% Latinx) who completed baseline visits and were re-assessed two years later. Fasting whole blood was ex vivo incubated with 4 stimulating agents reflecting microbial and sterile triggers of inflammation, and with 2 inhibitory agents, followed by assays for IL-1β, IL-6, IL-8, and TNF-α. Blood also was assayed for 6 circulating biomarkers of low-grade inflammation: C-reactive protein, interleukin-6, -8, and -10, tumor necrosis factor-α, and soluble urokinase-type plasminogen activator receptor. Using machine learning, levels of 15 p.m.2.5 constituents were estimated for a 50 m grid around children's homes. Models were adjusted for age, sex, race, pubertal status, and household income. In cross-sectional analyses, higher neighborhood PM2.5 was associated with larger cytokine responses to the four stimulating agents. These associations were strongest for constituents released by motor vehicles and soil/crustal dust. In longitudinal analyses, residential PM2.5 was associated with declining sensitivity to inhibitory agents; this pattern was strongest for constituents from fuel/biomass combustion and motor vehicles. By contrast, PM2.5 constituents were not associated with the circulating biomarkers of low-grade inflammation. Overall, these findings suggest the possibility of a trained immunity scenario, where PM2.5 heightens inflammatory cytokine responses to multiple stimulators, and dampens sensitivity to inhibitors which counter-regulate these responses.

Characteristics and source apportionment of water-soluble organic nitrogen (WSON) in PM2.5 in Hong Kong: With focus on amines, urea, and nitroaromatic compounds

Water-soluble organic nitrogen (WSON) is ubiquitous in fine particulate matter (PM2.5) and poses health and environmental risks. However, there is limited knowledge regarding its comprehensive speciation and source-specific contributions. Here, we conducted chemical characterization and source apportionment of WSON in 65 PM2.5 samples collected in Hong Kong during a 1-yr period. Using various mass-spectrometry-based techniques, we quantified 22 nitrogen-containing organic compounds (NOCs), including 17 nitroaromatics (NACs), four amines, and urea. The most abundant amine and NACs were dimethylamine and 4-nitrocatechol, respectively. Two secondary (i.e., secondary formation and secondary nitrate) and five primary sources (i.e., sea salt, fugitive dust, marine vessels, vehicle exhaust, and biomass burning) of WSON and these three categories of NOCs were identified. Throughout the year, secondary sources dominated WSON formation (69.0%), while primary emissions had significant contributions to NACs (77.1%), amines (75.9%), and urea (83.7%). Fugitive dust was the leading source of amines and urea, while biomass burning was the main source of NACs. Our multi-linear regression analysis revealed the significant role of sulfate, NO3, nitrate, liquid water content, and particle pH on WSON formation, highlighting the importance of nighttime NO3 processing and heterogeneous and aqueous-phase formation of NOCs in the Hong Kong atmosphere.

High loadings of carbonaceous aerosols from wood smoke in the atmosphere of Beijing from 2015 to 2017: Implications for energy transition policy

Recently, biomass has been regarded as a promising option for solid energy in China, which is promoted in the residential sector and firing power plants. We collected 200 PM2.5 samples (particulate matter with a aerodynamic diameter smaller than 2.5 μm) at multi-sites across Beijing from three individual sampling cases from 2015 to 2017. The levels of OC, OC fractions, EC, EC fractions, as well as K+ were measured. Then, we adopted the Positive Matrix Factorization 5.0 to apportion the sources of carbonaceous aerosols. The source apportionment results were compared with the estimates of source contribution using the bottom-up technical method with the latest emission inventories after the Action Plan was put into effect in 2013. Our results demonstrate that high pollution of carbonaceous aerosols originated from wood smoking based on the receptor modeling and bottom-up technical method in Beijing from 2015 to 2017. Future energy transition policy should focus on the technologies and regulations for reducing emissions from renewable biomass fuel combustion. This study highlights the importance of regulations that address emissions controls on fuels replacing coal combustion to meet the needs to mitigate air pollution from primary energy use.

Contribution of water-soluble extracts to the oxidative and inflammatory effects of atmospheric aerosols: A critical review

Exposure to atmospheric particulate matter (PM) has been associated with heightened risks of lung cancer, cardiovascular and respiratory diseases. PM exposure also affects the immune system, leading to an increased susceptibility to infections, exacerbating pre-existent inflammatory and allergic lung diseases. Atmospheric PM can primarily impact human health through the generation of reactive oxygen species (ROS) that subsequently induce or exacerbate inflammation. These cytotoxic effects have been related with PM concentration, and its chemical constituents, including metals, solvent extractable organics (e.g., polycyclic aromatic hydrocarbons), and water-soluble ions. Although not receiving much attention, the fine aerosol water-soluble organic matter (WSOM) can account for a substantial portion of the overall fine PM mass and has been shown to present strong oxidative and immunomodulatory effects. Thus, the objective of this review is to provide a comprehensive analysis of the role of the water-soluble fraction of PM, with a specific focus on the contribution of the WSOM component to the cytotoxic properties of atmospheric PM. The chemical properties of the water-soluble PM fraction are briefly discussed, while emphasis is put on how PM size, composition, and temporal variations (e.g., seasonality) can impact the pro-oxidative activity, the modulation of inflammatory response, and the cytotoxicity of the water-soluble PM extracts.

Investigating PM2.5 toxicity in highly polluted urban and industrial areas in the Middle East: human health risk assessment and spatial distribution

Exposure to particulate matter (PM) can be considered as a factor affecting human health. The aim of this study was to investigate the concentration of PM2.5 and heavy metals and their influence on survival of A549 human lung cells in exposure to PM2.5 breathing air of Ahvaz city. In order to assess the levels of PM2.5 and heavy metals, air samples were collected from 14 sampling stations positioned across Ahvaz city during both winter and summer seasons. The concentration of heavy metals was determined using ICP OES. Next, the MTT assay [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] was employed to ascertain the survival rate of A549 cells. The findings from this research demonstrated that average PM2.5 of the study period was (149.5 μg/m3). Also, the average concentration of PM2.5 in the urban area in winter and summer was (153.3- and 106.9 μg/m3) and in the industrial area this parameter was (191.6 and 158.3 μg/m3). The average concentration of metals (ng/m3) of urban areas against industrial, Al (493 vs. 485), Fe (536 vs. 612), Cu (198 vs. 212), Ni (128 vs. 129), Cr (48.5 vs. 54), Cd (118 vs. 124), Mn (120 vs. 119), As (51 vs. 67), Hg (37 vs. 50), Zn (302 vs. 332) and Pb (266 vs. 351) were obtained. The results of the MTT assay showed that the highest percentage of cell survival according to the exposure concentration was 25 > 50 > 100 > 200. Also, the lowest percentage of survival (58.8%) was observed in the winter season and in industrial areas with a concentration of 200 μg/ml. The carcinogenic risk assessment of heavy metals indicated that except for Cr, whose carcinogenicity was 1.32E-03, other metals were in the safe range (10-4-10-6) for human health. The high concentration of PM2.5 and heavy metals can increase respiratory and cardiovascular diseases and reduce the public health level of Ahvaz citizens.

Ambient particle characteristics by single particle aerosol mass spectrometry at a coastal site in Hong Kong: a case study affected by the sea-land breeze

The sea-land breeze (SLB) circulation plays a vital role in the transport of atmospheric pollutants in coastal cities. In this study, a single particle aerosol mass spectrometer (SPAMS) and combined bulk aerosol instruments were deployed to investigate the ambient particle characteristic at a suburban coastal site in Hong Kong from February 22 to March 10, 2013. Significant SLB circulations were captured from March 6-10, 2013, during the campaign. During the SLB periods, air quality worsened, with PM_2.5 concentrations reaching a peak of 55.6 μg m^-3 and an average value of 42.8 ± 4.5 μg m^-3. A total of 235,894 particles were measured during the SLB stage. Eight major sources were identified by investigating the mixing states of the total particles, including the coal-burning related particles (48.1%), biomass burning particles (6.7%), vehicle emission-related particles (16.4%), sea salt (9.2%), ship emission particles (2.7%), dust/steeling industries (3.7%), waste incineration (6.3%), and road dust (3.9%). It was noteworthy that the PM_2.5 concentrations and particle numbers increased sharply during the transition of land wind to the sea breeze. Meanwhile, the continental sourced pollutants recirculated back to land resulting in a cumulative increase in pollutants. Both individual and bulk measurements support the above results, with high contributions from coal burning, biomass burning, bulk K⁺, and NO₃ ^-, which were probably from the regional transportation from the nearby area. In contrast, the ship and vehicle emissions increased during the SLB period, with a high sulfate concentration partially originating from the ship emission. In this study, field evidence of continental-source pollutants backflow to land with the evolution of sea breeze was observed and helped our current understanding of the effect of SLB on air quality in the coastal city.

Determination of 31 Polycyclic Aromatic Hydrocarbons in Plant Leaves Using Internal Standard Method with Ultrasonic Extraction-Gas Chromatography-Mass Spectrometry

The method for the determination of 16 priority polycyclic aromatic hydrocarbons (PAHs) in plant leaves has been studied extensively, yet the quantitativemethod for measuring non-priority PAHs in plant leaves is limited. A method for the simultaneous determination of 31 polycyclic aromatic hydrocarbons (PAHs) in plant leaves was established using an ultrasonic extraction-gas chromatography-mass spectrometry-internal standard method. The samples of plant leaves were extracted with ultrasonic extraction and purified with solid-phase extraction columns. The PAHs were separated by using gas chromatography-mass spectrometry equipped with a DB-EUPAH capillary column (20 m × 0.18 mm × 0.14 μm) with a selective ion monitoring (SIM) detection mode, and quantified with an internal standard. The method had good linearity in the range of 0.005~1.0 μg/mL with correlation coefficients greater than 0.99, and the method detection limit and maximum quantitative detection limit were in the ranges of 0.2~0.7 μg/kg and 0.8~2.8 μg/kg, respectively. The method was verified with spiked recovery experiments. The average spiked recovery ranged from 71.0% to 97.6% and relative standard deviations (n = 6) were less than 14%. Herein, we established a quantitativemethod for the simultaneous determination of priority and non-priority PAHs in plant leaves using GC-MS. The method is highly sensitive and qualitatively accurate, and it is suitable for the determination of PAHs in plant leaves.

The Effects of Indoor Air Filter on Reductions in PM2.5 Associated Health Risks of Respiratory Function in Mouse

This study aimed to assess whether protective measures could reduce the health risks of air pollution in mice living in the chambers situated at a suburban site in Beijing. The living chambers of mice were divided into four groups: male mice with and without the high-efficiency particulate air (HEPA) filter (male group A and group B), as well as female mice with and without the HEPA filter (female group A and group B). The experiment was carried out from 1 December 2017 to 31 May 2018. Parameters of respiratory function during periods of clean air and air pollution were determined for all groups to evaluate the role of the indoor air filter (i.e., HEPA) in protection against respiratory health risks in mice. Significant differences in minute volumes were observed in male and female groups with versus without the HEPA. Additionally, respiratory health parameters including respiratory rate, duration of breaking, expiratory time, and relaxation time exhibited differences in female groups with HEPA versus without HEPA. Levels of inflammatory factors in the lungs were measured for all groups after 6months of exposure. Greater mean levels of IL-6 and TNF-α were found in the male groups without HEPA than in those with HEPA. Higher average concentrations of IL-6, T-AOC, SOD, GSH-Px, LDH, TNF-α, and TGF-β1 were found in the female group without HEPA than those without HEPA. Our study has proved the effective protection provided by indoor air filters (i.e., HEPA filters) in reducing respiratory health risks associated with PM2.5.

Polyphenylene sulfide fabric with enhanced oxidation resistance and hydrophobicity through polybenzoxazine surface coating for emission control in harsh environment

Emissions from power generation and municipal waste incineration sources are primarily at high temperatures and contain corrosive gases, particulate pollutants and are enormously challenging on the performance of the filtration systems in use. Here, polyphenylene sulfide (PPS) nonwoven fabric, a primary material used commercially in such settings, is modified with a polybenzoxazine precursor as a coating to deliver improved thermal and oxidation resistance to the fibrous substrate. The polybenzoxazine precursor undergoes chain propagation and crosslinking upon the treatment process to provide a protective layer over the PPS fibers such that enhanced structural stability in a harsh environment was demonstrated. We have shown the improved overall tensile strength (+15%), Young's modulus (+26%), and more hydrophobic nature of the modified PPS fabric, while the superior environmental stability and better filtration performance could be achieved. Such methodology may lead to higher service temperature and extended service time of the PPS filtration bags in harsh fire exhaustion airstreams encountered in power plants or municipal garbage incineration facilities. The crosslinkable benzoxazine could also be the most cost-effective high temperature coating layer on fibers, enabling future high-performance air filtration materials.

Associations of Exposure to Fine Particulate Matter Mass and Constituents with Systemic Inflammation: A Cross-Sectional Study of Urban Older Adults in China

Systemic inflammation is a key mechanism in the development of cardiovascular diseases induced by exposure to fine particles (particles with aerodynamic diameter ≤2.5 μm [PM_2.5]). However, little is known about the effects of chemical constituents of PM_2.5 on systemic inflammation. In this cross-sectional study, filter samples of personal exposure to PM_2.5 were collected from community-dwelling older adults in Tianjin, China, and the chemical constituents of PM_2.5 were analyzed. Blood samples were collected immediately after the PM_2.5 sample collection. Seventeen cytokines were measured as targets. A linear regression model was applied to estimate the relative effects of PM_2.5 and its chemical constituents on the measured cytokines. A positive matrix factorization model was employed to distinguish the sources of PM_2.5. The calculated source contributions were used to estimate their effects on cytokines. After adjusting for other covariates, higher PM_2.5-bound copper was significantly associated with increased levels of interleukin (IL)1β, IL6, IL10, and IL17 levels. Source analysis showed that an increase in PM_2.5 concentration that originated from tire/brake wear and cooking emissions was significantly associated with enhanced levels of IL1β, IL6, tumor necrosis factor alpha (TNFα), and IL17. In summary, personal exposure to some PM_2.5 constituents and specific sources could increase systemic inflammation in older adults. These findings may explain the cardiopulmonary effects of specific particulate chemical constituents of urban air pollution.

Insight into urban PM2.5 chemical composition and environmentally persistent free radicals attributed human lung epithelial cytotoxicity

Fine particulate matter (PM2.5) is detrimental to the human respiratory system. However, the toxicity of PM2.5 and its associated potentially harmful species, notably novel pollutants like environmentally persistent free radicals (EPFRs), remains unclear. Therefore, one-year site monitoring and ambient air PM2.5 sampling in the Nanjing urban area was designed to investigate the relationships between chemical compositions (carbon fractions, metallic elements, and water-soluble ions) and EPFRs, and change in cytotoxicity with varying PM2.5 components. Oxidative stress (reactive oxygen species, ROS), inflammatory injury (IL-6 and TNF-α), and membrane injury (LDH) of human lung epithelial cells (A549) induced by PM2.5 were analyzed using in vitro cytotoxicity test. Both the composition and toxicity of PM2.5 from different seasons were compared. The average daily exposure of urban PM2.5 associated EPFRs load in Nanjing were 2.29 × 1011 spin m-3. Their exposure concentration and cytotoxic damage ability were stronger in the cold season than warm. The particle compositions of metals and carbon fractions were significantly positively correlated with EPFRs. The airborne EPFRs, organic carbon (OC), and heavy metal Cu, As, and Pb may pose principal cell damage ability, which is worthy of further study interlinking aerosol pollution and health risks.

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.

Quantitative estimation of meteorological impacts and the COVID-19 lockdown reductions on NO2 and PM2.5 over the Beijing area using Generalized Additive Models (GAM)

Unprecedented travel restrictions due to the COVID-19 pandemic caused remarkable reductions in anthropogenic emissions, however, the Beijing area still experienced extreme haze pollution even under the strict COVID-19 controls. Generalized Additive Models (GAM) were developed with respect to inter-annual variations, seasonal cycles, holiday effects, diurnal profile, and the non-linear influences of meteorological factors to quantitatively differentiate the lockdown effects and meteorology impacts on concentrations of nitrogen dioxide (NO2) and fine particulate matters (PM2.5) at 34 sites in the Beijing area. The results revealed that lockdown measures caused large reductions while meteorology offset a large fraction of the decrease in surface concentrations. GAM estimates showed that in February, the control measures led to average NO2 reductions of 19 μg/m3 and average PM2.5 reductions of 12 μg/m3. At the same time, meteorology was estimated to contribute about 12 μg/m3 increase in NO2, thereby offsetting most of the reductions as well as an increase of 30 μg/m3 in PM2.5, thereby resulting in concentrations higher than the average PM2.5 concentrations during the lockdown. At the beginning of the lockdown period, the boundary layer height was the dominant factor contributing to a 17% increase in NO2 while humid condition was the dominant factor for PM2.5 concentrations leading to an increase of 65% relative to the baseline level. Estimated NO2 emissions declined by 42% at the start of the lockdown, after which the emissions gradually increased with the increase of traffic volumes. The diurnal patterns from the models showed that the peak of vehicular traffic occurred from about 12pm to 5pm daily during the strictest control periods. This study provides insights for quantifying the changes in air quality due to the lockdowns by accounting for meteorological variability and providing a reference in evaluating the effectiveness of control measures, thereby contributing to air quality mitigation policies.

Shenlian extract protects against ultrafine particulate matter-aggravated myocardial ischemic injury by inhibiting inflammation response via the activation of NLRP3 inflammasomes

Air pollution is a growing public health burden associated with several negative health effects, especially cardiovascular disease. Shenlian extract (SL), a traditional Chinese medicine, has the effects of clearing heat-toxin and promoting blood circulation for removing blood stasis, and it has long been used to treat cardiovascular diseases and atherosclerosis. This study explored the underlying action mechanism of SL against ultrafine particle-induced myocardial ischemic injury (UFP-MI) through network pharmacology prediction and experimental verification. Male Sprague-Dawley rats with UFP-MI were pre-treated with SL intragastrically for 7 days. All the rats were then euthanized. Inflammatory cytokine detection and histopathological analysis were performed to assess the protective effects of SL. For the mechanism study, differentially expressed genes (DEGs) were identified in UFP-MI rats treated with SL through transcriptomic analysis. Subsequently, in combination with network pharmacology, potential pathways involved in the effects of SL treatment were identified using the Internet-based Computation Platform (www.tcmip.cn) and Cytoscape 3.6.0. Further validation experiments were performed to reveal the mechanism of the therapeutic effects of SL on UFP-MI. The results show that SL significantly suppressed inflammatory cell infiltration into myocardial tissue and exhibited significant anti-inflammatory activity. Transcriptomic analysis revealed that the DEGs after SL treatment had significant anti-inflammatory, immunomodulatory, and anti-viral activities. Network pharmacology analysis illustrated that the targets of SL were mainly involved in regulation of the inflammatory response, apoptotic process, innate immune response, platelet activation, and coagulation process. By combining transcriptomic and network pharmacology data, we found that SL may exert anti-inflammatory effects by acting on the NOD-like signaling pathway to regulate immune response activation and inhibit systemic inflammation. Verification experiments revealed that SL can suppress the secretion of the inflammatory cytokines Interleukin-1 (IL-1), Interleukin-18(IL-18) and Interleukin-33(IL-33) and suppress NLRP3 inflammasome activity. The results suggested that SL can directly inhibit the activation of NLRP3 inflammasomes and reduce the release of cytokines to protect against ultrafine particulate matter-aggravated myocardial ischemic injury.

Cell cycle arrest of human bronchial epithelial cells modulated by differences in chemical components of particulate matter

There is increasing interest in understanding the role of airborne chemical components in modulating the cell cycle of human bronchial epithelial (HBE) cells that is associated with burden of cardiopulmonary disease. To address this need, our study collected ambient PM₁₀ (particles with aerodynamic diameter less than or equal to 10 μm) and PM_2.5 (particles with aerodynamic diameter less than or equal to 2.5 μm) across four sampling sites in Beijing during the year of 2015. Chemical components including organic carbon (OC), elemental carbon (EC), polycyclic aromatic hydrocarbons (PAHs), metals and water soluble ions were determined. Spearman's rank-order correlation was performed to examine the associations between chemical components in ambient particles and cell cycle distributions with p-values adjusted by Bonferroni methodology. Our results demonstrated the significant associations between certain chemical compositions (i.e., PAHs, EC, As and Ni) and percentages of HBE cells in G0/G1 and G1/G2 phases, respectively. Our results highlighted the need to reduce the specific toxins (e.g., PAHs, EC, As and Ni) from ambient particles to protect cardiopulmonary health associated with air pollution. Future study may focus on illustrating the mechanism of certain chemical compositions in altering the cell cycle in HBE cells.

The interaction laws of atmospheric heavy metal ions and water-soluble organic compounds in PM2.5 based on the excitation-emission matrix fluorescence spectroscopy

The excitation-emission matrix (EEM) fluorescence spectroscopy was used to characterize the fluorescence properties of water-soluble organic compounds (WSOCs) in PM_2.5 coupled with parallel factor analysis (PARAFAC). Three main components of WSOCs were extracted from PM_2.5, i.e., humic-like (fulvic acid-like and humic acid-like) substances (HULIS), and soluble microbial by-product-like or aromatic protein-like, respectively. A fluorescence quenching experiment was designed to systematically analyze the interaction laws of atmospheric heavy metal ions and WSOCs in PM_2.5. Our study revealed HULIS, especially the humic acid-like substances, might be principal substances binding with metal ions and the strength of interactions was related to the types and concentrations of metal ions. Furthermore, EEM was a powerful tool to understand the interaction laws of atmospheric heavy metal ions and WSOCs in PM_2.5. This work implied that the interactions of atmospheric heavy metal ions and WSOCs might directly or indirectly play a significant role in atmospheric environment and public health.

Competing PM2.5 and NO2 holiday effects in the Beijing area vary locally due to differences in residential coal burning and traffic patterns

The holiday effect is a useful tool to estimate the impact on air pollution due to changes in human activities. In this study, we assessed the variations in concentrations of fine particulate matter (PM_2.5) and nitrogen dioxide (NO₂) during the holidays in the heating season from 2014 to 2018 based on daily surface air quality monitoring measurements in Beijing. A Generalized Additive Model (GAM) is used to analyze pollutant concentrations for 34 sites by comprehensively accounting for annual, monthly, and weekly cycles as well as the nonlinear impacts of meteorological factors. A Saturday effect was found in the downtown area, with about 4% decrease in PM_2.5 and 3% decrease in NO₂ relative to weekdays. On Sundays, the PM_2.5 concentrations increased by about 5% whereas there were no clear changes for NO₂. In contrast to the small effect of the weekend, there was a strong holiday effect throughout the region with average increases of about 22% in PM_2.5 and average reductions of about 11% in NO₂ concentrations. There was a clear geographical pattern in the strength of the holiday effect. In rural areas the increase in PM_2.5 is related to the proportion of coal and biomass consumption for household heating. In the suburban areas between the Fifth Ring Road and Sixth Ring Road there were larger reductions in NO₂ than downtown which might be due to decreased traffic as many people return to their hometown for the holidays. This study provides insights into the pattern of changes in air pollution due to human activities. By quantifying the changes, it also provides insights for improvements in air quality due to control policies implemented in Beijing during the heating season.

Mechanism of PM2.5-induced human bronchial epithelial cell toxicity in central China

Exposure to PM_2.5 has been linked to respiratory disorders, yet knowledge of the molecular mechanism is limited. Here, PM_2.5 was monitored and collected in central China, and its cytotoxicity mechanism on human bronchial epithelial cells (BEAS-2B) was investigated. With the average concentration of 109 ± 69 μg/m³, PM_2.5 was rich in heavy metals and organic pollutants. After exposure to PM_2.5, the viability of BEAS-2B cells decreased, where 510 dysregulated genes were predicted to induce necroptosis via inhibiting ATP synthesis through the oxidative phosphorylation signaling pathway. Cellular experiments demonstrated that the content of ATP was downregulated, while the expression of RIP3, a necroptosis indicator, was upregulated. Besides, four enzymes in charge of ATP synthesis were downregulated, including ATP5F, NDUF, COX7A, and UQCR, while two genes of RELA and CAPN1 responsible for necroptosis were upregulated. Furthermore, N-acetylcysteine was applied as an enhancer for ATP synthesis, which reversed the downregulation of ATP5F, NDUF, and COX7A, and consequently alleviated the elevation of RELA, CAPN1, and RIP3. In conclusion, PM_2.5 exposure downregulates ATP5F, NDUF, COX7A, and UQCR, and that inhibits ATP synthesis via the oxidative phosphorylation signaling pathway, which subsequently upregulates RELA and CAPN1 and ultimately leads to necroptosis of BEAS-2B cells.

Oxidative potential of ambient PM2.5 in Wuhan and its comparisons with eight areas of China

Oxidative potential (OP) is a good indicator for assessing health risk associated with exposure to fine particulate matter (PM_2.5, <2.5 μm in aerodynamic diameter). In this study, 24-h ambient PM_2.5 samples were collected at three sampling sites throughout selected months of 2012 in Wuhan, Central China. Water soluble ions, metals, organic carbon (OC), elemental carbon (EC), levoglucosan, polycyclic aromatic hydrocarbons (PAHs), hopanes, and dicarboxylic acids were determined. The dithiothreitol (DTT) assay was used to characterize the oxidative potential of PM_2.5. Linear regression analysis and principal component analysis (PCA) were used to link OP to the individual redox-active components originating from diverse emission sources. The OP results from the three sites in Wuhan, combined with the findings from eight other field studies of OP conducted in China, were compiled in order to compare the OP data in developed countries. The average, normalized OP levels for volume and mass at the three sampling sites in Wuhan were in the range of 1.8-8.2 nmol min^-1 m^-3 and 18.2-52.8 nmol min^-1 mg^-1, respectively. The differences in OP levels across sampling sites depended on the temporal and spatial differences in redox-active components of PM_2.5. Results from linear regression and PCA showed that the redox-active components emitted from secondary inorganic aerosols as well as secondary organic aerosols were associated with the volume normalized OP in Wuhan. Two notable findings are illustrated by synthesizing the OP results observed at multi-sites across China. Of the nine field studies conducted in China, the lowest measured mass-normalized OP levels are significantly higher than the highest OP levels from field studies conducted in developed continents. China shares the same sources responsible for OP (e.g., secondary sources, fuel combustion, biomass burning, and dust emissions) with several other countries in developed continents.