Fine Particulate Matter-Induced Oxidative Stress Mediated by UVA-Visible Light Leads to Keratinocyte Damage.

The human skin is exposed to various environmental factors including solar radiation and ambient air pollutants. Although, due to its physical and biological properties, the skin efficiently protects the body against the harm of environmental factors, their excessive levels and possible synergistic action may lead to harmful effects. Among particulate matter present in ambient air pollutants, PM2.5 is of particular importance for it can penetrate both disrupted and intact skin, causing adverse effects to skin tissue. Although certain components of PM2.5 can exhibit photochemical activity, only a limited amount of data regarding the interaction of PM2.5 with light and its effect on skin tissue are available. This study focused on light-induced toxicity in cultured human keratinocytes, which was mediated by PM2.5 obtained in different seasons. Dynamic Light Scattering (DLS) and Atomic Force Microscopy (AFM) were employed to determine sizes of the particles. The ability of PM2.5 to photogenerate free radicals and singlet oxygen was studied using EPR spin-trapping and time-resolved singlet oxygen phosphorescence, respectively. Solar simulator with selected filters was used as light source for cell treatment to model environmental lightning conditions. Cytotoxicity of photoexcited PM2.5 was analyzed using MTT assay, PI staining and flow cytometry, and the apoptotic pathway was further examined using Caspase-3/7 assay and RT-PCR. Iodometric assay and JC-10 assay were used to investigate damage to cell lipids and mitochondria. Light-excited PM2.5 were found to generate free radicals and singlet oxygen in season-dependent manner. HaCaT cells containing PM2.5 and irradiated with UV-Vis exhibited oxidative stress features-increased peroxidation of intracellular lipids, decrease of mitochondrial membrane potential, enhanced expression of oxidative stress related genes and apoptotic cell death. The data indicate that sunlight can significantly increase PM2.5-mediated toxicity in skin cells.

Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses.

A direct approach to limit airborne viral transmissions is to inactivate them within a short time of their production. Germicidal ultraviolet light, typically at 254 nm, is effective in this context but, used directly, can be a health hazard to skin and eyes. By contrast, far-UVC light (207-222 nm) efficiently kills pathogens potentially without harm to exposed human tissues. We previously demonstrated that 222-nm far-UVC light efficiently kills airborne influenza virus and we extend those studies to explore far-UVC efficacy against airborne human coronaviruses alpha HCoV-229E and beta HCoV-OC43. Low doses of 1.7 and 1.2 mJ/cm2 inactivated 99.9% of aerosolized coronavirus 229E and OC43, respectively. As all human coronaviruses have similar genomic sizes, far-UVC light would be expected to show similar inactivation efficiency against other human coronaviruses including SARS-CoV-2. Based on the beta-HCoV-OC43 results, continuous far-UVC exposure in occupied public locations at the current regulatory exposure limit (~3 mJ/cm2/hour) would result in ~90% viral inactivation in ~8 minutes, 95% in ~11 minutes, 99% in ~16 minutes and 99.9% inactivation in ~25 minutes. Thus while staying within current regulatory dose limits, low-dose-rate far-UVC exposure can potentially safely provide a major reduction in the ambient level of airborne coronaviruses in occupied public locations.

Investigating photo-driven arsenics' behavior and their glucose metabolite toxicity by the typical metallic oxides in ambient PM2.5.

It is essential and challenged to understand the atmospheric arsenic pollution because it is much more complicated than in water and top-soil. Herein the different behavior of arsenic species firstly were discovered within the ambient PM2.5 collected during daytime and nighttime, winter and summer. The diurnal variation of arsenic species in PMs is significantly correlated with the presence of metallic oxides, specifically, ferrous, titanium and zinc oxides, which might play a key role in the process of the photo-oxidation of As(III) to As(V) with the meteorological parameters and regional factors excluded. Subsequently, the photo conversion of arsenite was detected on metal-loaded glass-fiber filters under visible light. The photo-generated superoxide radical was found to be predominantly responsible for the oxidation of As(III). In order to reveal toxicity differences induced by oxidation As(III), HepG2 cells were exposed to various arsenic mixture solution. We found that the antioxidant enzyme activities suppressed with increasing the As(III)/As(V) ratio in total, followed by the accumulation of intracellular ROS level. The glucose consumption and glycogen content also displayed an obvious reduction in insulin-stimulated cells. Compared to the expression levels of IRS-1, AKT and GLUT4, GLUT2 might be more vulnerable to arsenic exposure and lead to the abnormalities of glucose metabolism in HepG2 cells. Taken together, these findings clarify that the health risk posed by inhalation exposure to As-pollution air might be alleviated owing to the photo-driven conversion in presence of metal oxides.

Impact of a novel mobile high-efficiency particulate air-ultraviolet air recirculation system on the bacterial air burden during routine care.

Aerosol transmission of pathogens can result in the rapid spread of disease. Introduction of a mobile air recirculation system based on high-efficiency particulate air filtration, photochemical oxidation, and germicidal ultraviolet light significantly decreased the bacterial load by over 40% under routine care in an emergency department. Application of this new technology promises to reduce the aerosol pathogen burden, thereby decreasing exposure risk and providing a safer environment for patient care.

Impacts of photochemical ageing on the half-lives and diagnostic ratio of polycyclic aromatic hydrocarbons intrinsic to PM2.5 collected from 'real-world' like combustion events of wood and rice straw burning.

The present experimental study describes the characteristics of polycyclic aromatic hydrocarbons (PAHs) emitted with PM2.5 particles during wood and rice straw burning as well as impacts of photochemical ageing on the half lives of particulate PAHs and their diagnostic ratio values. The photochemical degradation kinetics experiments were carried out by exposing the PM2.5 to light and synthetic air flow. Pseudo first order rate constants were calculated based on PAH loss as a function of exposure time. Relatively quick degradation of lighter PAHs (3-rings) [(0.2-0.5)h-1] than heavier PAHs (4-6 rings) [(0.0005-0.03)h-1] indicates substantial impact of PAH-substrate interaction through π-π stacking with the carbonaceous substrates. Moreover, our results showed distinct PAH diagnostic ratios (DR) for wood and rice straw burnings which, however, change with time due to photochemical degradation. The later may add uncertainties in the applications of DR values for source apportionment. Furthermore, considerably large half lives (100-3000 h) of the carcinogenic PAHs as estimated under ambient solar radiation may cause poor and adverse air quality in long range and therefore demands immediate regulations against uncontrolled biomass burning.

Temperature Dependence of Photodegradation of Dissolved Organic Matter to Dissolved Inorganic Carbon and Particulate Organic Carbon.

Photochemical transformation of dissolved organic matter (DOM) has been studied for more than two decades. Usually, laboratory or "in-situ" experiments are used to determine photodegradation variables. A common problem with these experiments is that the photodegradation experiments are done at higher than ambient temperature. Five laboratory experiments were done to determine the effect of temperature on photochemical degradation of DOM. Experimental results showed strong dependence of photodegradation on temperature. Mathematical modeling of processes revealed that two different pathways engaged in photochemical transformation of DOM to dissolved inorganic carbon (DIC) strongly depend on temperature. Direct oxidation of DOM to DIC dominated at low temperatures while conversion of DOM to intermediate particulate organic carbon (POC) prior to oxidation to DIC dominated at high temperatures. It is necessary to consider this strong dependence when the results of laboratory experiments are interpreted in regard to natural processes. Photodegradation experiments done at higher than ambient temperature will necessitate correction of rate constants.

DNA damage caused by inorganic particulate matter on Raji and HepG2 cell lines exposed to ultraviolet radiation.

Epidemiological studies have correlated exposure to ultraviolet-irradiated particulate matter with cardiovascular, respiratory, and lung diseases. This study investigated the DNA damage induced by two major inorganic particulate matter compounds found in diesel exhaust, ammonium nitrate and ammonium sulfate, on Burkitt's lymphoma (Raji) and hepatocellular carcinoma (HepG2) cell lines. We found a dose-dependent positive correlation of accumulated DNA damage at concentrations of ammonium nitrate (25 µg/ml, 50 µg/ml, 100 µg/ml, 200 µg/ml, 400 µg/ml) with ultraviolet exposure (250 J/m(2), 400 J/m(2), 600 J/m(2), 850 J/m(2)), as measured by the comet assay in both cell lines. There was a significant difference between the treated ammonium nitrate samples and negative control samples in Raji and HepG2 cells (p<0.001). Apoptosis was shown in Raji and HepG2 cells when exposed to high concentrations of ammonium nitrate (200 µg/ml and 400 µg/ml) for 1h in samples without ultraviolet exposure, as assessed by the comet assay. However, the level of apoptosis greatly diminished after ultraviolet exposure at these concentrations. Over a 24h period, at intervals of 1, 4, 8, 12, 18, and 24h, we also observed that ammonium nitrate decreased viability in Raji and HepG2 cell lines and inhibited cell growth. Ammonium sulfate-induced DNA damage was minimal in both cell lines, but there remained a significant difference (p<0.05) between the ultraviolet radiation treated and negative control samples. These results indicate that the inorganic particulate compound, ammonium nitrate, induced DNA strand breaks at all concentrations, and indications of apoptosis at high concentrations in Raji and HepG2 cells, with ultraviolet radiation preventing apoptosis at high concentrations. We hypothesize that ultraviolet radiation may inhibit an essential cellular mechanism, possibly involving p53, thereby explaining this phenomenon. Further studies are necessary to characterize the roles of apoptosis inhibition induced by DNA damage caused by inorganic particulate matter.

Lateral optical force on chiral particles near a surface.

Light can exert radiation pressure on any object it encounters and that resulting optical force can be used to manipulate particles. It is commonly assumed that light should move a particle forward and indeed an incident plane wave with a photon momentum hk can only push any particle, independent of its properties, in the direction of k. Here we demonstrate, using full-wave simulations, that an anomalous lateral force can be induced in a direction perpendicular to that of the incident photon momentum if a chiral particle is placed above a substrate that does not break any left-right symmetry. Analytical theory shows that the lateral force emerges from the coupling between structural chirality (the handedness of the chiral particle) and the light reflected from the substrate surface. Such coupling induces a sideway force that pushes chiral particles with opposite handedness in opposite directions.

Real-time detection of airborne asbestos by light scattering from magnetically re-aligned fibers.

Inadvertent inhalation of asbestos fibers and the subsequent development of incurable cancers is a leading cause of work-related deaths worldwide. Currently, there is no real-time in situ method for detecting airborne asbestos. We describe an optical method that seeks to address this deficiency. It is based on the use of laser light scattering patterns to determine the change in angular alignment of individual airborne fibers under the influence of an applied magnetic field. Detection sensitivity estimates are given for both crocidolite (blue) and chrysotile (white) asbestos. The method has been developed with the aim of providing a low-cost warning device to trades people and others at risk from inadvertent exposure to airborne asbestos.

Soft-X-ray-enhanced electrostatic precipitation for protection against inhalable allergens, ultrafine particles, and microbial infections.

Protection of the human lung from infectious agents, allergens, and ultrafine particles is difficult with current technologies. High-efficiency particulate air (HEPA) filters remove airborne particles of >0.3 µm with 99.97% efficiency, but they are expensive to maintain. Electrostatic precipitation has been used as an inexpensive approach to remove large particles from airflows, but it has a collection efficiency minimum in the submicrometer size range, allowing for a penetration window for some allergens and ultrafine particles. Incorporating soft X-ray irradiation as an in situ component of the electrostatic precipitation process greatly improves capture efficiency of ultrafine particles. Here we demonstrate the removal and inactivation capabilities of soft-X-ray-enhanced electrostatic precipitation technology targeting infectious agents (Bacillus anthracis, Mycobacterium bovis BCG, and poxviruses), allergens, and ultrafine particles. Incorporation of in situ soft X-ray irradiation at low-intensity corona conditions resulted in (i) 2-fold to 9-fold increase in capture efficiency of 200- to 600-nm particles and (ii) a considerable delay in the mean day of death as well as lower overall mortality rates in ectromelia virus (ECTV) cohorts. At the high-intensity corona conditions, nearly complete protection from viral and bacterial respiratory infection was afforded to the murine models for all biological agents tested. When optimized for combined efficient particle removal with limited ozone production, this technology could be incorporated into stand-alone indoor air cleaners or scaled for installation in aircraft cabin, office, and residential heating, ventilating, and air-conditioning (HVAC) systems.

Low-frequency ultrasound induces oxygen vacancies formation and visible light absorption in TiO2 P-25 nanoparticles.

Low-frequency ultrasound (LFUS) irradiation induces morphological, optical and surface changes in the commercial nano-TiO(2)-based photocatalyst, Evonik-Degussa P-25. Low-temperature electron spin resonance (ESR) measurements performed on this material provided the first experimental evidence for the formation of oxygen vacancies (V(o)), which were also found responsible for the visible-light absorption. The V(o) surface defects might result from high-speed inter-particle collisions and shock waves generated by LFUS sonication impacting the TiO(2) particles. This is in contrast to a number of well-established technologies, where the formation of oxygen vacancies on the TiO(2) surface often requires harsh technological conditions and complicated procedures, such as annealing at high temperatures, radio-frequency-induced plasma or ion sputtering. Thus, this study reports for the first time the preparation of visible-light responsive TiO(2)-based photocatalysts by using a simple LFUS-based approach to induce oxygen vacancies at the nano-TiO(2) surface. These findings might open new avenues for synthesis of novel nano-TiO(2)-based photocatalysts capable of destroying water or airborne pollutants and microorganisms under visible light illumination.

Low to negligible photoactivity of lake-water matter in the size range from 0.1 to 5 µm.

We found that the photochemical generation of reactive transients such as singlet oxygen and triplet states upon irradiation of different lake water samples is mostly accounted for by components smaller than 0.10 µm. Larger components often showed a much lower absorption and/or scattering of radiation compared with the smaller ones, with one exception where the minor to negligible photochemical activity of larger species was associated with significant radiation absorption/scattering. It is also shown that filtration of the lake water samples at 0.10 µm was able to effectively remove the suspended particles, differently from the usually suggested filtration at 0.45 µm.

Ultraviolet absorption properties of suspended particulate matter in untreated surface waters.

Previous research has shown that wastewater disinfection using UV light can be impaired by attenuation of the UV light as it passes through particles to reach embedded and protected microorganisms. This study determined that the UV absorption (at 254 nm) of particles present in 10 untreated surface waters was similar to the absorption of wastewater particles. As such, it provides evidence that UV disinfection of surface waters during drinking water treatment may be impaired by the same mechanism if particles are present. The study also demonstrated that among the 10 untreated surface waters examined, there was no correlation between the UV absorption (254 nm) of the solid particulate material, total organic carbon, total suspended solids, turbidity, or UV absorbance (254) of the bulk water.

Ultrasonic particle size fractionation in a moving air stream.

Identification of bio-aerosol particles may be enhanced by size sorting before applying analytical techniques. In this paper, the use of ultrasonic acoustic radiation pressure to continuously size fractionate particles in a moving air stream is described. Separate particle-laden and clean air streams are introduced into a channel and merged under laminar flow conditions. An ultrasonic transducer, mounted flush to one wall of the channel, excites a standing ultrasonic wave perpendicular to the flow of the combined air stream. Acoustic radiation forces on the particles cause them to move transverse to the flow direction. Since the radiation force is dependent upon the particle size, larger particles move a greater transverse distance as they pass through the standing wave. The outlet flow is then separated into streams, each containing a range of particle sizes. Experiments were performed with air streams containing glass microspheres with a size distribution from 2-22 microm, using a centerline air stream velocity of approximately 20 cm/s. An electrostatic transducer operating at a nominal frequency of 50 kHz was used to drive an ultrasonic standing wave of 150 dB in pressure amplitude. The microsphere size distributions measured at the outlet were compared with the predictions of a theoretical model. Experiments and theory show reasonable correspondence. The theoretical model also indicates an optimal partitioning of the particle-laden and clean air inlet streams.

DRIFTS studies on the photodegradation of tannic acid as a model for HULIS in atmospheric aerosols.

Humic like substances (HULIS) are important components of atmospheric aerosols, yet little is known about their photochemical transformation and the role of adsorbed water in this photochemistry. We report herein in situ and surface-sensitive spectroscopic studies on (1) the photodegradation of solid tannic acid, (2) structure of adsorbed water before and after photodegradation, and (3) the change in the hydrophilicity of tannic acid as a result of this photochemistry. Tannic acid (TA) was chosen as a synthetic proxy for HULIS because it has a defined molecular structure. Photochemical studies were conducted using diffuse reflectance infrared spectroscopy (DRIFTS) as a function of time (3 h), relative humidity (5-30%) and total irradiance (7, 20, 290 W m(-2) at 555 nm). Water adsorption isotherm measurements were recorded before and after photodegradation, which provided information on the structure of interfacial water and the thermodynamics of adsorption. The structure of water adsorbed on TA resembles that of water at the interface with polar organic solvents. Difference spectral data collected during irradiation shows loss features in the 1700-1000 cm(-1) range and growth in carbonyl features that are blue shifted relative to the starting material, suggesting oxidative photodegradation of TA and formation of aryl aldehydes. Under our experimental conditions, we observed no enhancement in water uptake after photodegradation relative to that on unirradiated samples. The implications of our results to the understanding of heterogeneous photochemistry of HULIS and the role of adsorbed water in these reactions are discussed.

Photoenhanced ozone loss on solid pyrene films.

This work presents the results of two complementary studies of the heterogeneous reaction of gas-phase ozone with solid pyrene films. In the first study, ozone uptake by the pyrene film was determined using a coated-wall flow tube system. In the second, pyrene loss within the film upon exposure to ozone was monitored using a laser-induced fluorescence technique. The dependence of the reactive loss rate on ozone concentration observed in both methods suggests that the reaction proceeds via a Langmuir-Hinshelwood-type surface mechanism. At a mixing ratio of 50 ppb, the steady-state reactive uptake coefficient of ozone by pyrene films increased from 5.0x10(-6) in the dark to 3.7x10(-5) upon exposure to near-UV radiation (300-420 nm). The uptake coefficient increased linearly as a function of UV-A spectral irradiance and decreased markedly with increasing relative humidity. The loss of surface pyrene upon exposure to ozone also displayed a light enhancement: analysis of Langmuir-Hinshelwood plots for the light and dark reactions revealed a small increase in the two-dimensional reaction rate in the presence of light (lambda>or=295 nm). This modest enhancement, however, was less significant than the corresponding enhancement in the loss of gas-phase ozone. In order to explain these observations, we present an integrated mechanism whereby the light-enhanced ozone uptake arises from the reaction of ozone with O2(1Sigmag+) formed via energy transfer from excited-state pyrene and the enhanced pyrene loss occurs via the formation of a charge-transfer complex between excited-state pyrene and adsorbed ozone. The disparity between surface- and gas-phase results underscores the important role that multifaceted strategies can play in elucidating the mechanisms of heterogeneous atmospheric reactions.

Activated toxicity of diesel particulate extract by ultraviolet a radiation in mammalian cells: role of singlet oxygen.

BACKGROUND: Diesel exhaust [diesel exhaust particles (DEPs) and their extracts (DPE)] and ultraviolet A radiation (UVA) are two ubiquitous environmental factors that have been identified as essential risk factors for various benign or malignant human diseases, either alone or in combination with other agents. OBJECTIVES: We aimed to investigate the synergistic effects of DPE and UVA at low-dose exposures in human-hamster hybrid (AL) cells and their underlying mechanisms. METHODS: We exposed exponentially growing AL cells to DPE and/or UVA radiation with or without reactive oxygen species (ROS) quenchers and then assayed the cells for survival, mutation induction, apoptosis, and micronucleus generation. In addition, using a singlet oxygen (1O2) trapping probe, 2,2,6,6-tetramethyl-4-piperidone, coupled with electron paramagnetic resonance spectroscopy, we determined the production of 1O2. RESULTS: Treatment of AL cells with DPE+UVA induced significant cytotoxic and genotoxic damage. In contrast, we found no significant damage in cells treated with either UVA or DPE alone at the same doses. Mutation spectra of CD59- mutants showed that treatment with DPE+UVA easily induces multilocus deletions. Sodium azide significantly inhibited both cellular and DNA damage induced by DPE+UVA treatment, whereas other ROS inhibitors had little protecting effect. Furthermore, we found a significant increase of 1O2 in the cells that received DPE+UVA treatment. CONCLUSION: These findings suggest that UVA activated the genotoxicity and cytotoxicity of DPE in mammalian cells and that 1O2 played an important role in these processes.

Contributions of toluene and alpha-pinene to SOA formed in an irradiated toluene/alpha-pinene/NO(x)/ air mixture: comparison of results using 14C content and SOA organic tracer methods.

An organic tracer method, recently proposed for estimating individual contributions of toluene and alpha-pinene to secondary organic aerosol (SOA) formation, was evaluated by conducting a laboratory study where a binary hydrocarbon mixture, containing the anthropogenic aromatic hydrocarbon, toluene, and the biogenic monoterpene, alpha-pinene, was irradiated in air in the presence of NO(x) to form SOA. The contributions of toluene and alpha-pinene to the total SOA concentration, calculated using the organic tracer method, were compared with those obtained with a more direct 14C content method. In the study, SOA to SOC ratios of 2.07 +/- 0.08 and 1.41 +/- 0.04 were measured for toluene and (alpha-pinene SOA, respectively. The individual tracer-based SOA contributions of 156 microg m(-3) for toluene and 198 microg m(-)3 for alpha-pinene, which together accounted for 82% of the gravimetrically determined total SOA concentration, compared well with the 14C values of 182 and 230 microg m(-3) measured for the respective SOA precursors. While there are uncertainties associated with the organic tracer method, largely due to the chemical complexity of SOA forming chemical mechanisms, the results of this study suggest the organic tracer method may serve as a useful tool for determining whether a precursor hydrocarbon is a major SOA contributor.

QSPRs on photodegradation half-lives of atmospheric chlorinated polycyclic aromatic hydrocarbons associated with particulates.

A quantitative structure-property relationship (QSPR) model which could predict photodegradation half-lives (t(1/2)) of chlorinated polycyclic aromatic hydrocarbons (ClPAHs) associated with particulates in the atmosphere was developed by applying quantum chemical parameters computed with quantum chemical PM3 algorithm and using a partial least squares (PLS) algorithm. The cross-validated Q(2)(cum) value for the optimal QSPR model is 0.960, indicating a good predictive capability for logt(1/2) values of ClPAHs. The QSPR results show that the main factors affecting logt(1/2) values of ClPAHs are the energy of the second highest occupied molecular orbital (E(LUMO-1)), the energy of the second highest occupied molecular orbital (E(HOMO+1)), average molecular polarizability (alpha), the most positive net atomic charges on a hydrogen atom (Q(H)(+)), E(LUMO)+E(HOMO), E(LUMO)-E(HOMO), and (E(LUMO)-E(HOMO))(2). ClPAHs with high E(LUMO-1), E(HOMO+1), E(LUMO)-E(HOMO,) and (E(LUMO)-E(HOMO))(2) values tend to photolyze slowly in the atmosphere. In contrast, increasing E(LUMO)+E(HOMO), alpha, and Q(H)(+) values leads to the increase of photodegradation rates.