Atmospheric Ultrafine Particles Research Articles

Comparison of aerosol number size distribution and new particle formation in summer at alpine and urban regions in the Guanzhong Plain, Northwest China

Ultrafine particles play a crucial role in understanding climate change, mitigating adverse health effects, and developing strategies for air pollution control. However, the factors influencing the occurrence and development of new particle formation (NPF) events, as well as the underlying chemical mechanisms, remain inadequately explained. This study compared number concentrations and size distributions of atmospheric ultrafine particles at Xi'an (urban area) and the summit of Mt. Hua (alpine region) in summer to investigate the NPF mechanism and particle growth in both clean and polluted areas of the Guanzhong Plain. The average particle number concentration in Xi'an was significantly higher than that at Mt. Hua. The diurnal variation of total particle number concentration differed between Xi'an and Mt. Hua indicating a divergence in influencing factors. The size distributions in Xi'an varied across different timescales and weather conditions, whereas Mt. Hua exhibited little variation. This stability at Mt. Hua is attributed to its cleaner background atmosphere and the steady influx of aging particles with larger diameters transported from the free atmosphere. In both areas, geometric mean diameters (GMDs) were inversely proportional to particle number concentrations suggesting that increase in particle numbers were primarily due to the generation of smaller particles. The potential governing factors for NPF events differed somewhat between the urban and mountainous stations. In the urban area, intense local stationary and mobile emission sources promoted the growth of newly formed nanoparticles, with ozone-oxidized condensable vapors serving as key precursors. In contrast, at the mountainous station, NPF process were significantly influenced by anthropogenic precursors from long-range transport and locally emitted biogenic organics. The rapid increase in ultrafine particle concentrations primarily poses serious health risks and degrades air quality in urban areas, while also contributing to climate-related effects in alpine regions.

Health risk assessment of ultrafine particle movement in children's residential spaces based on probabilistic neural networks

The air quality in children's living spaces has a significant impact on their health, and ultrafine particulate matter (PM2.5), as one of the main pollutants in the air, poses a particularly prominent threat to children's respiratory and immune systems. Therefore, it important to conduct health risk assessment on ultrafine particle exercise in children's living spaces. In this article, an intelligent risk assessment model of ultrafine atmospheric particles in children's sports space in residential areas based on probabilistic neural network (PNN) is studied. This model utilizes probabilistic neural networks to monitor and predict ultrafine particles in residential spaces, evaluating their potential risks to children's health. By collecting relevant data such as particulate matter concentration and air quality index in residential spaces, and using probabilistic neural networks for training and prediction, accurate assessment of the health risks of ultrafine particulate matter during exercise can be achieved. This model can be applied to densely populated places such as families and schools, providing parents and relevant institutions with scientific risk warning and prevention measures to ensure the health and safety of children. Probabilistic neural networks can learn and simulate complex nonlinear relationships, making the model more accurate in predicting the concentration of ultrafine particles and health risks. So as to construct a method system of health risk assessment of atmospheric particles, and the model is heavy metal elements in atmospheric fine particles, and corresponding improvement measures are put forward according to the assessment results. For circulatory system diseases, the degree of harm of atmospheric temperature and fine particles to children's health is basically close, and with the continuous decline of temperature, the synergistic effect of the two is more obvious. The concentration of atmospheric ultrafine particles significantly affects the health risk of children's sports activities space. All the experiments in this article are quite good. Among them, the average accuracy of the PNN health risk identification model is 0.840, and the average recall rate is 0.837. The health risk assessment model in this article strengthens the correlation of data information through scientific methods, grasps the basic information of children's sports activity spaces in residential areas, and formulates targeted sports health risk assessments for children's sports activity spaces in residential areas. Compared with the comparison method, the response speed is significantly improved, with an accuracy rate of over 90%.

Seasonal variations in composition and sources of atmospheric ultrafine particles in urban Beijing based on near-continuous measurements

Abstract. Understanding the composition and sources of atmospheric ultrafine particles (UFPs) is essential in evaluating their exposure risks. It requires long-term measurements with high time resolution, which are scarce to date. We performed near-continuous measurements of UFP composition during four seasons in urban Beijing using a thermal desorption chemical ionization mass spectrometer, accompanied by real-time size distribution measurements. We found that UFPs in urban Beijing are dominated by organic components, varying seasonally from 68 % to 81 %. CHO organics (i.e., molecules containing carbon, hydrogen, and oxygen) are the most abundant in summer, while sulfur-containing organics, some nitrogen-containing organics, nitrate, and chloride are the most abundant in winter. With the increase of particle diameter, the contribution of CHO organics decreases, while that of sulfur-containing and nitrogen-containing organics, nitrate, and chloride increases. Source apportionment analysis of the UFP organics indicates contributions from cooking and vehicle sources, photooxidation sources enriched in CHO organics, and aqueous/heterogeneous sources enriched in nitrogen- and sulfur-containing organics. The increased contributions of cooking, vehicle, and photooxidation components are usually accompanied by simultaneous increases in UFP number concentrations related to cooking emission, vehicle emission, and new particle formation, respectively, while the increased contribution of the aqueous/heterogeneous composition is usually accompanied by the growth of UFP mode diameters. The highest UFP number concentrations in winter are due to the strongest new particle formation, the strongest local primary particle number emissions, and the slowest condensational growth of UFPs to larger sizes. This study provides a comprehensive understanding of urban UFP composition and sources and offers valuable datasets for the evaluation of UFP exposure risks.

Nonequilibrium Behavior in Isoprene Secondary Organic Aerosol.

Recent studies have shown that instantaneous gas-particle equilibrium partitioning assumptions fail to predict SOA formation, even at high relative humidity (∼85%), and photochemical aging seems to be one driving factor. In this study, we probe the minimum aging time scale required to observe nonequilibrium partitioning of semivolatile organic compounds (SVOCs) between the gas and aerosol phase at ∼50% RH. Seed isoprene SOA is generated by photo-oxidation in the presence of effloresced ammonium sulfate seeds at <1 ppbv NOx, aged photochemically or in the dark for 0.3-6 h, and subsequently exposed to fresh isoprene SVOCs. Our results show that the equilibrium partitioning assumption is accurate for fresh isoprene SOA but breaks down after isoprene SOA has been aged for as short as 20 min even in the dark. Modeling results show that a semisolid SOA phase state is necessary to reproduce the observed particle size distribution evolution. The observed nonequilibrium partitioning behavior and inferred semisolid phase state are corroborated by offline mass spectrometric analysis on the bulk aerosol particles showing the formation of organosulfates and oligomers. The unexpected short time scale for the phase transition within isoprene SOA has important implications for the growth of atmospheric ultrafine particles to climate-relevant sizes.

Detection of silver nanoparticles inside leaf of European beech (Fagus sylvatica L.)

In a greenhouse experiment, silver nanoparticles (Ag-NPs) were applied on European beech (Fagus sylvatica L.) leaves using the droplet application method. Scanning electron microscopy (SEM) analyses showed that after 24 h silver nanoparticles were mostly present in aggregates or as single particles on the surface of the leaf, surrounding or covering the stomata. Analyses of cross sections of the leaf revealed that some silver nanoparticles were adhering to the cell walls of the mesophyll and palisade cells, most likely after penetration into the leaf through the stomata as particles and not as Ag ions. Our preliminary results showed evidence of foliar uptake of silver nanoparticles in European beech. This opens new insights on the ability of trees to take up solid nanosized particles, eventually contained in raindrops, through their leaves, and potentially transport them to other parts of the tree. This study would be helpful for investigating the role of trees in atmospheric ultrafine particle mitigation.

High Pressure Inside Nanometer-Sized Particles Influences the Rate and Products of Chemical Reactions.

The composition of organic aerosol has a pivotal influence on aerosol properties such as toxicity and cloud droplet formation capability, which could affect both climate and air quality. However, a comprehensive and fundamental understanding of the chemical and physical processes that occur in nanometer-sized atmospheric particles remains a challenge that severely limits the quantification and predictive capabilities of aerosol formation pathways. Here, we investigated the effects of a fundamental and hitherto unconsidered physical property of nanoparticles-the Laplace pressure. By studying the reaction of glyoxal with ammonium sulfate, both ubiquitous and important atmospheric constituents, we show that high pressure can significantly affect the chemical processes that occur in atmospheric ultrafine particles (i.e., particles < 100 nm). Using high-resolution mass spectrometry and UV-vis spectroscopy, we demonstrated that the formation of reaction products is strongly (i.e., up to a factor of 2) slowed down under high pressures typical of atmospheric nanoparticles. A size-dependent relative rate constant is determined and numerical simulations illustrate the reduction in the production of the main glyoxal reaction products. These results established that the high pressure inside nanometer-sized aerosols must be considered as a key property that significantly impacts chemical processes that govern atmospheric aerosol growth and evolution.

Development and Application of a Wide Dynamic Range and High Resolution Atmospheric Aerosol Water-Based Supersaturation Condensation Growth Measurement System

The supersaturated condensation of atmospheric aerosol is important in the study of mechanisms of cloud condensation and even heavy air pollution. The existing technology cannot realize accurate dynamic control of wide range supersaturation, so it is difficult to study condensation growth characteristics of nanoparticles through different levels of supersaturation. Here, a supersaturated condensation growth measurement system with three-stage microscope pipes was developed. The resolution of supersaturated condensation system is 0.14, within the range of 0.92 to 2.33 after calibration. Stabilization time is only about 80 s for saturation range 0.92–1.01, which helps to control saturation rapidly, and the control deviation of saturation is no more than 0.06. Measurement of different supersaturated condensation growth control conditions showed that, the particle size increased significantly compared with hygroscopic growth at high humidity. For single-component particles, the increase in size increased to a similar size at the same saturation, with a difference within 7.4%. The increase in size for ammonium sulfate (AS) increased by 13.4–30.2% relative to that of glucose. For the mixed-component, the increase in size decreased about 15.9–25.0% with the increase of the glucose. Because the glucose coating on the surface of AS have hindered particle growth. This also shows that atmospheric ultrafine particles, especially inorganic salt particles, will rapidly grow into larger particles under supersaturated conditions such as increased environmental humidity, thus having some impact on environmental pollution and climate change.

Sulfuric acid–amine nucleation in urban Beijing

Abstract. New particle formation (NPF) is one of the major sources of atmospheric ultrafine particles. Due to the high aerosol and trace gas concentrations, the mechanism and governing factors for NPF in the polluted atmospheric boundary layer may be quite different from those in clean environments, which is however less understood. Herein, based on long-term atmospheric measurements from January 2018 to March 2019 in Beijing, the nucleation mechanism and the influences of H2SO4 concentration, amine concentrations, and aerosol concentration on NPF are quantified. The collision of H2SO4–amine clusters is found to be the dominating mechanism to initialize NPF in urban Beijing. The coagulation scavenging due to the high aerosol concentration is a governing factor as it limits the concentration of H2SO4–amine clusters and new particle formation rates. The formation of H2SO4–amine clusters in Beijing is sometimes limited by low amine concentrations. Summarizing the synergistic effects of H2SO4 concentration, amine concentrations, and aerosol concentration, we elucidate the governing factors for H2SO4–amine nucleation for various conditions.

Acute Exposure of Atmospheric Ultrafine Particles Induced Inflammation Response and Dysregulated TGFβ/Smads Signaling Pathway in ApoE-/- Mice.

Ultrafine particles (UFPs) referred to particular matters with aerosol diameter less than 100nm. Because of the lightweight and small size, UFPs have become an occupational inhalation risk. The UFPs will be accumulated in the deep lung through inhalation, and then reach into all the organs via circulation system; some UFPs even stay in the brain. As previous study reported, UFPs exposure is usually associated with cardiovascular disease, such as atherosclerosis (AS). In our study, we tried to understand how acute UFP exposure caused the biological dysregulation in atherosclerosis. Acute exposure of UFPs were applied to mice for 6 consecutive days, mice were sacrificed after 3, 5, 7, and 10days post-exposure. Aorta and serum were collected for histological and biomarkers analysis. Mice aortic adventitial fibroblasts (MAFs) were isolated from mice and used to further study to understand the mechanism of UFPs induced atherosclerosis. Compared to the untreated control, the inflammation responses and nitrate stress were observed after acute exposure of UFPs, with increased IL-6, MCP-1, p47phox, and 3-NT levels in the mice serum. Besides, upregulation of microRNAs: miR-301b-3p and Let-7c-1-3p, and their downstream target: Smad2, Smad3, and TGFβ1 were also observed in mouse aorta after acute exposure of UFPs. Similar results were identified in vitro as well. Acute exposure of UFPs induced the systematic nitrate stress and inflammation responses, along with the changes of vascular permeability. Dysregulated miRNAs and TGFβ/Smads signaling pathway indicated the higher risk of atherosclerosis/vasculature remodeling when exposed to UFPs.

Exploring the toxic effects and mechanism of lead-loaded ultrafine carbon black on lysozyme

Abstract As an important part of atmospheric ultrafine particles (UFPs), the safety evaluation of ultrafine carbon black (UFCB) has been a hot topic of discussion among researchers. In this work, we studied and compared the interaction of ultrafine carbon black (P35) with lysozyme before and after lead loading and their effects on protein structure. Scanning electron microscope, Zeta potential, Fourier transform infrared spectroscopy and particle size analysis were used to characterize the surface characteristics, dispersion, and particle size distribution of UFCB after ozone modification. Steady-state fluorescence spectroscopy, synchronous fluorescence spectroscopy, ultraviolet spectrophotometry and circular dichroism were used to evaluate the effect of UFCB on the structure of lysozyme before and after lead loading. The results showed that the hydrophobicity of protein amino acids before and after lead loading both showed a weakening trend, but after the adsorption of lead, the secondary structure stability of lysozyme is lower than that before lead loading. The results of the enzyme activity assay showed that the lead-loaded ultrafine carbon black (UFCB-Pb) caused a significant decrease in lysozyme activity compared to the change in the absence of lead. This study, therefore, provides fundamental information on the toxic effects of lead-loaded ultrafine carbon black on proteins, and offers beneficial idea for exploring the combined pollution of ultrafine particles.

CEN standard “Harmonized counting of atmospheric ultrafine particles” and UFP monitoring initiatives in Europe

The paper is devoted the standard CEN/TS 16976 described a standardized measuring method with number concentration of UFP. As well as, described TSI 3750-CEN CPC which meet all of these requirements.

A human embryonic stem cell-based in vitro model revealed that ultrafine carbon particles may cause skin inflammation and psoriasis

Air pollution has been linked to many health issues, including skin conditions, especially in children. Among all the atmospheric pollutants, ultrafine particles have been deemed very dangerous since they can readily penetrate the lungs and skin, and be absorbed into the bloodstream. Here, we employed a human embryonic stem cell (hESC)-based differentiation system towards keratinocytes, to test the effects of ultrafine carbon particles, which mimic ambient ultrafine particles, at environment related concentrations. We found that 10 ng/mL to 10 μg/mL ultrafine carbon particles down-regulated the expression of the pluripotency marker SOX2 in hESCs. Moreover, 1 μg/mL to 10 μg/mL carbon particle treatments disrupted the keratinocyte differentiation, and up-regulated inflammation- and psoriasis-related genes, such as IL-1β, IL-6, CXCL1, CXCL2, CXCL3, CCL20, CXCL8, and S100A7 and S100A9, respectively. Overall, our results provide a new insight into the potential developmental toxicity of atmospheric ultrafine particles.

A soft X-ray unipolar charger for ultrafine particles

The performance of a unipolar particle charger using soft X-ray as the ion production source was optimized and characterized in this study. The charger design was based on the high efficiency particle charger reported by Chen and Pui (1999), in which the radioactive material (210Po) as the ion source and sheath flow for minimizing the particle loss were used. The use of 210Po source makes it challenging for field investigation due to the regulation of controlled substances. The inclusion of sheath flow in the high efficiency charger inevitably dilutes the output particle concentration, which is an undesired effect for the measurement of atmospheric ultrafine particles. The current soft X-ray charger was designed to ease the above concerns. The penetration efficiency, intrinsic and extrinsic charging efficiency, and extrinsic charge distributions of particles passing through the charger were measured under the optimal voltage operation. It was found that the loss of ultrafine particles in the charger was higher than that in the high efficiency charger (due to the lack of applying sheath flow). At the flow rate of 5.0 lpm, the measured extrinsic charging efficiency was comparable to that of the charger applied in the thermal desorption chemical ionization mass spectrometer (Smith et al., 2004). The measured extrinsic charge distribution of particles further showed that more than 50% of particles in the size range of 20–40 nm and 20–50 nm were singly charged at the flow rate of 1.5 lpm and 5.0 lpm, respectively.

Exposure to Atmospheric Ultrafine Particles Induces Severe Lung Inflammatory Response and Tissue Remodeling in Mice.

Exposure to particulate matter (PM) is leading to various respiratory health outcomes. Compared to coarse and fine particles, less is known about the effects of chronic exposure to ultrafine particles, despite their higher number and reactivity. In the present study, we performed a time-course experiment in mice to better analyze the lung impact of atmospheric ultrafine particles, with regard to the effects induced by fine particles collected on the same site. Trace element and PAH analysis demonstrated the almost similar chemical composition of both particle fractions. Mice were exposed intranasally to FF or UFP according to acute (10, 50 or 100 µg of PM) and repeated (10 µg of PM 3 times a week during 1 or 3 months) exposure protocols. More particle-laden macrophages and even greater chronic inflammation were observed in the UFP-exposed mice lungs. Histological analyses revealed that about 50% of lung tissues were damaged in mice exposed to UFP for three months versus only 35% in FF-exposed mice. These injuries were characterized by alveolar wall thickening, macrophage infiltrations, and cystic lesions. Taken together, these results strongly motivate the update of current regulations regarding ambient PM concentrations to include UFP and limit their emission.

Growth Kinetics and Size Distribution Dynamics of Viscous Secondary Organic Aerosol.

Low bulk diffusivity inside viscous semisolid atmospheric secondary organic aerosol (SOA) can prolong equilibration time scale, but its broader impacts on aerosol growth and size distribution dynamics are poorly understood. Here, we present quantitative insights into the effects of bulk diffusivity on the growth and evaporation kinetics of SOA formed under dry conditions from photooxidation of isoprene in the presence of a bimodal aerosol consisting of Aitken (ammonium sulfate) and accumulation (isoprene or α-pinene SOA) mode particles. Aerosol composition measurements and evaporation kinetics indicate that isoprene SOA is composed of several semivolatile organic compounds (SVOCs), with some reversibly reacting to form oligomers. Model analysis shows that liquid-like bulk diffusivities can be used to fit the observed evaporation kinetics of accumulation mode particles but fail to explain the growth kinetics of bimodal aerosol by significantly under-predicting the evolution of the Aitken mode. In contrast, the semisolid scenario successfully reproduces both evaporation and growth kinetics, with the interpretation that hindered partitioning of SVOCs into large viscous particles effectively promotes the growth of smaller particles that have shorter diffusion time scales. This effect has important implications for the growth of atmospheric ultrafine particles to climatically active sizes.

Impacts of Future European Emission Reductions on Aerosol Particle Number Concentrations Accounting for Effects of Ammonia, Amines, and Organic Species.

Although they are currently unregulated, atmospheric ultrafine particles (<100 nm) pose health risks because of, e.g., their capability to penetrate deep into the respiratory system. Ultrafine particles, often minor contributors to atmospheric particulate mass, typically dominate aerosol particle number concentrations. We simulated the response of particle number concentrations over Europe to recent estimates of future emission reductions of aerosol particles and their precursors. We used the chemical transport model PMCAMx-UF, with novel updates including state-of-the-art descriptions of ammonia and dimethylamine new particle formation (NPF) pathways and the condensation of organic compounds onto particles. These processes had notable impacts on atmospheric particle number concentrations. All three emission scenarios (current legislation, optimized emissions, and maximum technically feasible reductions) resulted in substantial (10-50%) decreases in median particle number concentrations over Europe. Consistent reductions were predicted in Central Europe, while Northern Europe exhibited smaller reductions or even increased concentrations. Motivated by the improved NPF descriptions for ammonia and methylamines, we placed special focus on the potential to improve air quality by reducing agricultural emissions, which are a major source of these species. Agricultural emission controls showed promise in reducing ultrafine particle number concentrations, although the change is nonlinear with particle size.

Characteristics of size-resolved atmospheric inorganic and carbonaceous aerosols in urban Shanghai

Size-segregated aerosol particles were collected with a 10-stage Micro-Orifice Uniform Deposit Impactor (MOUDI) at an urban site in Shanghai, China for four non-consecutive months representing four seasons from 2015 to 2016. Chemical composition, including water-soluble ions as well as organic carbon (OC), elemental carbon (EC) and secondary organic carbon (SOC) of size-resolved (0.056–18 μm) atmospheric aerosols in four seasons and in different polluted cases were studied. The size distributions of sulfate, nitrate and ammonium (SNA) and carbonaceous aerosol (OC, EC and SOC) were discussed and the potential sources of PM1.8-associated secondary species (SO42−, NO3−, SNA and SOC) in different seasons were identified by potential source contribution function (PSCF) model. Results showed that atmospheric ultrafine and fine particle pollution in Shanghai were very serious during the study period. Most of the water-soluble ions tended to be enriched in fine particles, especially being abundant in the droplet mode in polluted cases. Compared with sulfate, size distributions of nitrate and ammonium presented more significant seasonal variations and showed distinctive characteristics in polluted days. Abundant nitrate was concentrated in fine particles in cold seasons (spring and winter), whereas it was enriched in coarse mode during summer and autumn. The droplet mode sulfate with high concentration did not result in the aggravation of air pollution, while the nucleation mode sulfate may have made a great contribution to the air pollution in urban Shanghai. It was also found that the formation of air pollution in urban Shanghai had a significant link with nitrate and ammonium, especially with nitrate and ammonium in condensation mode and droplet mode, and the contribution of sulfate to the pollution formation in Shanghai would somehow be surpassed by the increasing nitrate and ammonium. OC and EC concentrations from spring to winter were found to be 11.10, 7.10, 12.30, 20.16, and 3.73, 2.84, 4.63, 7.10 μg m−3, respectively, distinctly presenting the summer minima and winter maxima in this study. The maximum OC/EC was in the droplet mode and the minimum was in the nucleation mode for both clean and polluted days. The great contribution of SOC to OC in droplet mode and the occurrence of PM pollution necessarily had an important bearing on the SOC formation in droplet mode particles. Particle acidity may play a key role in secondary organic aerosol formation and the particles with the size of 0.056–0.1 μm was the most sensitive particles to acid catalysis in SOA formation. The similar PSCF results of PM1.8-associated SOC to those of SO42−, NO3− and SNA indicated possible connections between the formation of SOC and secondary inorganic species in PM.

CHARACTERISTICS OF ELEMENTAL AND ORGANIC CARBON IN ATMOSPHERIC NANOPARTICLES AT DIFFERENT SAMPLING LOCATIONS IN VIETNAM

Atmospheric ultrafine particles (NPs or PM0.1) were investigated at a roadside of Nguyen Van Cu road (Vinacomin) and at a mixed site in the Hanoi University of Science and Technology (HUST) in Hanoi, Vietnam. The sampling was conducted during a rainy reason and a dry season to determine the characteristics of atmospheric elemental and organic carbon in the nanoparticles. The relative contributions of organic carbon (OC) and elemental carbon (EC) to total carbon (TC) at HUST were 83.7 – 85.0% and 15.0–16.3 %, respectively; whereas those at Vinacomin’s sampling site accounted for 78.6 – 81.5% and 18.5 – 21.4 %, respectively. The study provides an interesting observation that particulate OC and EC have spatial and temporal variations dependent on sampling sites and weather conditions. In contrast, consistent OC/EC ratios were also found at both seasons of each location, in which the ratios were from 3.68 to 5.68. The correlations of OC and EC were found in the rainy season with the slopes ranging from 0.21–0.34; however, these correlations were not observed in the dry season. The relationships between OC and EC, char – EC and soot – EC can be used in primarily determining the sources of NPs in the atmosphere.

Exploratory assessment of indoor and outdoor particle number concentrations in Hanoi households

No studies have been conducted in Vietnam to understand the levels of atmospheric ultrafine particles, despite having adverse health effects. Information about indoor air quality in Vietnam is also limited. Hence we aimed to conduct the first assessment of ultrafine particle concentrations in terms of particle number (PN) in Hanoi, by simultaneously measuring indoor and outdoor PN concentrations from six households at different locations across the city in January 2016. We also acquired PM2.5 data for this monitoring period from an air quality monitoring station located at the US Embassy in Hanoi, to compare the general trends between PN and PM2.5 concentrations. The mean daily indoor and outdoor PN concentrations for the monitoring period were 1.9×104p/cm3 and 3.3×104p/cm3, respectively, with an increase during rush hour traffic. It was concluded that traffic was the main contributor to outdoor PN concentrations, with agricultural burning having a small influence at one study location. The mean ratio of indoor to outdoor PN concentrations for all six sites was 0.66±0.26, which points to outdoor air as the main driver of indoor PN concentrations, rather than indoor sources. These PN concentrations and I/O ratios are similar to those reported for a number of cities in developed countries. However, in contrast to PN, ambient mean PM2.5 concentrations in Hanoi (60–70μg/m3) were significantly higher than those typically recorded in developed countries. These findings demonstrate that urban particle mass (PM2.5) concentrations are not indicative of the PN concentrations, which can be explained by different sources contributing to PN and PM, and that direct measurements of PN are necessary to provide information about population exposure to ultrafine particles and for management of air quality.

Silica nanoparticles and lead acetate co-exposure triggered synergistic cytotoxicity in A549 cells through potentiation of mitochondria-dependent apoptosis induction

The adverse effects of PM2.5 are the results of combined toxicities of finer particles and their adsorbed toxic pollutants. Nevertheless, the combined toxicity of finer particles and air pollutants still remains unclear. The present study was therefore undertaken to investigate the combined cytotoxicity of silica nanoparticles (nano-SiO2, a typical atmospheric ultrafine particle) and lead acetate (Pb, a representative air pollutant) in A549 cells focusing on mitochondria-dependent apoptosis induction. The results showed that Pb exposure alone induced mitochondria-dependent apoptosis in A549 cells, as evidenced by increased apoptotic rate and Bax/Bcl-2 ratio, up-regulated caspases 3 and 9 expressions as well as decreased mitochondrial membrane potential. Non-cytotoxic concentration of nano-SiO2 exposure alone did not trigger apoptosis in A549 cells, but potentialized the apoptotic changes when co-exposure with Pb. Factorial analyses revealed synergistic interactions were responsible for the potentiation of joint apoptotic responses.