Surface Area Concentration Research Articles

New Insights on the Size-Dependent Inhibition of Enzymes by Gold Nanoparticles.

Particle size might affect the inhibition behaviors of gold nanoparticles (AuNPs) on enzyme activity by influencing the density of binding sites (ρ), the association constant (Ka), the steric hindrance of enzymes by AuNPs, the binding orientations of the enzyme on AuNPs, as well as the structural changes of enzymes. In previous studies, the effects of the above-mentioned factors, which could not be ignored in the applications of enzymatic electrochemistry, were often overshadowed by the effects of surface area. In order to study the size effect on the inhibition types and inhibitory ability of enzymes by AuNPs, we investigated the inhibition behaviors of chymotrypsin (ChT) by AuNPs with three different sizes (D1-AuNCs, D3-AuNPs, and D6-AuNPs) under the same surface area concentration. The results showed that both of the inhibition types and the inhibition ability varied with the particle size of AuNPs. D1-AuNCs inhibited ChT noncompetitively, while D3/D6-AuNPs inhibited ChT competitively. Contrary to the common sense, D6-AuNPs showed a weaker inhibitory ability than D3-AuNPs. By means of zeta potential, agarose gel electrophoresis, isothermal titration calorimetry, synchronous fluorescence spectroscopy, and circular dichroism, the mechanism of the weak inhibitory ability of D6-AuNPs was found to be the standing binding orientation caused by the small curvature. This work had certain guiding significance for the biosafety of AuNPs, the development of nanoinhibitors, as well as the applications of AuNPs in enzymatic electrochemistry.

Measuring the Surface Area Concentration and Specific Surface Area of Mass-Produced Graphene Nanoflakes via Fluorescence Quenching

A primitive cubic lattice composed of 1,000 atoms has 488 surface sites. By definition, every atom in a strictly two-dimensional single-layer lattice composes its surface. These surface atoms are the ones that undergo chemical interactions with the surrounding medium, thereby defining the functionalities of the nanostructure. As such, one of the most important morphological properties of nano-objects is the extremely large specific surface area that enhances their levels of reactivity. Here, we introduce an optical spectroscopy method to measure the surface area concentration, ρA, of mass-produced graphene nanoflakes in liquid dispersions. The information is accessed from the quenching of the fluorescence signal from the dye molecules dispersed in the medium. We found that the quantum efficiency of the fluorescence signal decays exponentially with the concentration of graphene’s surface area, the decay rate being independent of the degree of exfoliation. If the mass concentration ρ is known by other means, the specific surface area can be extracted from the ratio ρA/ρ. The measurements can be performed directly in liquid suspensions of nanoflakes, being highly applicable to the quality control of mass-produced two-dimensional nanomaterials, especially by means of mechanically assisted liquid-phase exfoliation.

Spatial distribution and proximity effect-dependent multi-enzyme cascades catalysis operating in dendritic mesoporous silica nanoparticles

Enzymatic cascades catalysis engenders complex and selective intracellular transformations due to the organization of the enzymes in confined cellular environments. In this work, a biomimetic strategy is employed to develop a synthetic cell analogue for operating multi-enzymatic cascade catalysis in vitro. The glucose peroxidase (GOx) and chloroperoxidase (CPO) are co-encapsulated in the channel of dendritic mesoporous silica nanoparticles (DMSP) modified by phase-transitioned lysozyme (PTL@GOx&CPO@DMSP). The cascade efficiency is substantially enhanced compared with the diffusion mixtures of the free enzymes in bulk solution due to some nanoscale construction, such as confinement effect, proximity effect and special distribution mode of the enzymes. The high specific surface area and high concentration of mesoporous cages in DMSP is beneficial for encapsulation of enzyme. The cross-linked cavities ensure directional transfer of the intermediate from GOx to CPO, known as “substrate channel”. PTL plays multiple functions including inhibiting leaking of enzyme from DMSP, concentrating intermediate H2O2 at DMSP domains and keeping this biocomposite stable in aqueous environment by improving its dispersibility. The prepared biocomposite PTL@GOx & CPO@DMSP is very stable at harsh conditions. It can retain 42% of original catalytic activity at 90°C with incubation for 3 h while the retained activity of free enzymes is only 5% under the same conditions. Meanwhile, it can keep 92.4% of its original catalytic activity after 10 reuses. These characteristics ensure practical application of this biocatalytic material. The active HClO generated by GOx-CPO cascade has an efficient anti-tumor effect and is effectively applied to preserve fruit.

126 A Laboratory Procedure and a Recording System for the Maintenance of Personal, Hand-Held and Benchtop Time-Resolved Aerosol Instruments

Abstract The HSE Science and Research Centre use time-resolved instruments to collect aerosol data for research and to support the sampling of aerosols in workplace environments. The performance of these instruments (traditional and low cost sensor devices) is dependent on regular maintenance and calibration. However, it can deteriorate within the recommended manufacturer calibration period, particularly if they have been exposed to high concentration of dust, or exposed for extended periods. This poster will describe the practical strategy developed at HSE for the maintenance of time-resolved devices and the lessons learnt. HSE owns a range of hand-held or compact time-resolved instruments, which are optical particle counters (OPCs), condensation particle counters (CPCs), diffusion chargers as well as photometers measuring particle number, surface area and mass concentrations. Some of the instruments are size-resolved devices. Photometers and OPCs were benchmarked using SPHERIGLASS ® A- 5000 in a calm-air chamber for a wide range of concentrations against a dedicated reference photometer or OPC, not necessarily of the same model or size range characteristic. For devices, measuring in the nanometre size range (CPCs and Diffusion Chargers), a salt nanoparticle aerosol was generated using a Collison nebulizer and a CPC used as the reference. Acceptable tolerances from the reference concentration were established for the CPCs and Diffusion Chargers. For each photometer model, an average ratio of the evaluated photometers concentrations by the reference photometers concentrations was calculated and a linearity plot of the photometer concentration versus the reference photometer concentration was established. © Crown Copyright (2022)

90 Graphene – Exposure and Emissions at Two Pilot Plants

Abstract Graphene is a nanomaterial suitable for a wide variety of applications. The industrial production and use of graphene is, hence, increasing rapidly. The main challenge in assessing graphene exposure is that graphene is a carbon structure, making it comparable to look for a needle in a haystack. We have explored the possibility to analyze elemental carbon and black carbon as a measure of personal graphene exposure. Exposure and emission measurements for graphene were conducted at two pilot plants using on- and off-line techniques. One plant produces graphene, up to 10 tons per year, using liquid exfoliation technique. The other plant uses graphene to coat paper in a conventional roll-to-roll process. The measurements were conducted both stationary (in the emission zone and in the background) and as personal measurements (in the breathing zone of the workers). We have analyzed elemental carbon and black carbon as a measure of the personal exposure. In the emission and background zone we have measured number of particles and lung deposited surface area concentration of particles <300nm, mass concentration, and we have collected samples for electron microscopy analysis. The exposure was in general low, but we identified tasks with an increase emissions. Measurements of elemental carbon is a promising technique for occupational hygienists to find possible exposure to graphene.

126 Emission and Exposure Characterization During Metal Waste Recycling

Abstract Waste of electrical and electronic equipment (WEEE) is one of the fastest-growing waste streams in the EU. The airborne occupational and environmental exposures generated by this waste handling are poorly quantified, and the growing use of nanomaterials in electronics adds to the uncertainty of risk assessment. Emission and personal exposure measurements were carried out during industrial recycling for three different metal waste flows: WEEE, metal scrap and cables. Size distributions and number-, mass- and lung deposited surface area concentrations were assessed by on-line techniques, and filter samples were collected for gravimetric analyses, metal content, and electron microscopy. Samples for elemental analyses with Particle Induced X-ray Emission (PIXE) was collected by a 12-stage low-pressure impactor . Additionally, low-cost sensors were deployed for long term monitoring. By number, the size distributions from all three flows were heavily dominated by particles <100 nm. Electron microscopy showed that there are many different elements in the same particle and that the composition of different particles vary considerably. Abundant elements, according to ICP-MS, were Fe, Al, Zn, and Cu, but Pb, Mn, Ba, and Co were also detected. PIXE analysis showed that the chemical composition indeed is different in different particle sizes, with e.g. Cr almost exclusively being present in particles < 200 nm. Low-cost sensors, not previously used for monitoring in highly polluted industrial settings, functioned well after 30 days. This study shows that detailed particle characterization is crucial for understanding of today’s and tomorrow’s waste recycling exposures, and as input to future toxicological assessments.

Mesoporous Hollow Manganese Doped Ceria Nanoparticle for Effectively Prevention of Hepatic Ischemia Reperfusion Injury.

Hepatic ischemia-reperfusion injury (HIRI) is the main reason for liver dysfunction or failure after liver resection and liver transplantation. As excess accumulation of reactive oxygen species (ROS) is the leading factor, ceria nanoparticle, a cyclic reversible antioxidant, is an excellent candidate for HIRI. Manganese doped mesoporous hollow ceria nanoparticles (MnOx-CeO2 NPs) were prepared, and the physicochemical characteristics, such as particle size, morphology, microstructure, etc. were elucidated. The in vivo safety and liver targeting effect were examined after i.v. injection. The anti-HIRI was determined by a mouse HIRI model. MnOx-CeO2 NPs with 0.40% Mn doped exhibited the strongest ROS-scavenging capability, which may due to the increased specific surface area and surface oxygen concentration. The nanoparticles accumulated in the liver after i.v. injection and exhibited good biocompatibility. In the HIRI mice model, MnOx-CeO2 NPs significantly reduced the serum ALT and AST level, decreased the MDA level and increased the SOD level in the liver, prevent pathological damages in the liver. MnOx-CeO2 NPs were successfully prepared and it could significantly inhibit the HIRI after i.v. injection.

The combined effects of heterogeneous chemistry and aerosol-radiation interaction on severe haze simulation by atmospheric chemistry model in Middle-Eastern China

Heterogeneous chemistry and aerosol-radiation interaction (ARI) are considered two of the key mechanisms affecting haze formation and their reasonable parameterizations in atmospherically chemical models play an important role in accurate haze or air quality prediction. However, until the present, their relative contributions to severe haze have rarely been evaluated. Using the double-way atmospherically chemical model GRAPES_Meso5.1/CUACE CW, the relative contributions of heterogeneous chemistry and ARI to PM2.5 are investigated under different pollution levels in Middle-Eastern China (MEC) during December 2016. Study results show that the combined effects of heterogeneous chemistry and ARI generate 29.7% of total PM2.5 mass in MEC of December 2016, of which ARI contributes 19.7%, much higher than heterogeneous chemistry (6.1%). However, heterogeneous chemistry is important for reasonable reproduction of the proportion of secondary inorganic aerosols (SIA) of PM2.5, especially during heavy haze. Both the contributions of heterogeneous chemistry and ARI to PM2.5 increase with the haze pollution aggravation but to different degrees. The contribution of heterogeneous chemistry to modeled PM2.5 concentration rises from 4.0% on clean days to 6.6% under moderate pollution and 7.8% under heavy haze. And that of ARI increases rapidly from 9.1% on clean days to 21.0% under moderate pollution and 29.1% during heavy pollution. It is worth noticing that there is an additional contribution to PM2.5 caused by the combination of heterogeneous chemistry and ARI except for their respective contributions, which reaches up to 7.3% of PM2.5 mass and 18.5% of SIA generation under heavily polluted conditions. This is because ARI further promotes heterogeneous oxidation of SO2 and NOx by increasing the aerosol surface area concentration (SAC), causing additional SIA production via heterogeneous pathways. This work indicates the contribution of ARI to severe haze formation not only by altering meteorological conditions but also by reforming the chemical processes in the model.

COx -free H2 Production via Catalytic Decomposition of CH4 over Fe Supported on Tungsten oxide-activated Carbon Catalyst: Effect of Tungsten Loading

Production of COx-free H2 from CH4 (a major global warming contributor) over cheap catalysts is a dominant task for the scientific community to accomplish environmental-friendly clean H2 energy sources. Herein, a tungsten oxide-activated carbon-supported Fe catalyst is prepared by impregnation method, characterized by X-ray diffraction, surface area-porosity measurement, temperature programmed reduction/oxidation and thermogravimetry analysis. 30wt.%Fe supported tungsten oxide incorporated activated carbon catalyst is found superior to 30 wt% Fe supported on activated carbon incorporated tungsten oxide due to higher surface area and high concentration of reducible catalytic active sites. 30wt.%Fe impregnated over 25 wt%WO3-75 wt%activated carbon support catalyst has the highest concentration of reducible surface-active species and it had excellent performance among other tungsten oxide incorporated catalysts. The catalyst showed 66.04% CH4 conversion, 63.12% H2 yield and YH2 /CCH4 > 0.9 initially which didn’t fall below 35 % up to 160-minutes. Improper matching between the rate of carbon formation and the rate of diffusion over a highly crystalline 30Fe50W50Ac catalyst resulted in rapid deactivation.

Effect of urban green infrastructure on pedestrian exposure to ultrafine particles: A case study of Guangzhou, China

Traffic emissions, as the dominant source of urban Ultrafine Particles (UFP), pose great potential health risks to pedestrians who commute near busy roads. Green infrastructure is regarded as an effective measure for urban particulate pollution abatement. In this study, two weeks of mobile measurements of pedestrian UFP exposure were performed during morning and evening rush hours, along greenway and sidewalk with and without vegetation barrier near an arterial road. UFP concentration was observed to be 28.7% lower with weakened fluctuations on vegetation barrier sidewalk than on open sidewalk in average, while UFP lung-deposited surface area concentration decreased by 21.1% accordingly. Vegetation mitigated UFP concentration in general, however, locally intense heavy-duty vehicles activities might weaken this effect occasionally. The weekly and diurnal variations of UFP concentration and the greenery effect performance were attributable to the combined effect of practical traffic situations, meteorological conditions, and crowd activities. Gray relational analysis indicated that temperature (γ = 0.814), relative humidity (γ = 0.787), traffic volume (γ = 0.764) and heavy-duty vehicles count (γ = 0.741) were the top four impact factors on roadside UFP concentration during observation.

Hydrogen Production by N-Heterocycle Dehydrogenation over Pd Supported on Aerogel-Prepared Mg-Al Oxides

Tetradecahydrophenazine (14HP) is a nitrogen-containing heterocycle compound with a high content of hydrogen that can be released during its dehydrogenation to phenazine (P). The high stability of the 14HP/P pair and relatively low dehydrogenation temperature make 14HP a promising organic hydrogen carrier. This manuscript is devoted to the investigation of hydrogen production by 14HP dehydrogenation over Pd supported on a series of magnesium-aluminum oxides prepared by the aerogel method. This technique made it possible to synthesize catalyst supports characterized by a high surface area and high concentration of surface active sites where active transition metals could be stabilized in a finely dispersed state. The synthesized aerogels had high specific surface areas and pore volumes. A surface area as high as 600 m2/g after calcination at 500 °C was observed for the mixed aerogel with an Mg:Al ratio of 1:4. An increase in the concentration of acidic electron-acceptor sites determined by EPR on the surface of the mixed magnesium-aluminum oxide supports with a high surface area prepared by the aerogel method was found to result in higher hydrogen production due to the faster dehydrogenation of sterically hindered nitrogen-containing tetradecahydrophenazine heterocycles.

Novel nanowire self-assembled hierarchical CeO2 microspheres loaded with nickel-based catalysts for hydrogen production from steam reforming of glycerol

The nickel-based catalysts with shape-specific CeO2 nanocrystals (hierarchical and spheres) and adjustable impregnation solvents were successfully synthesized. The synthesized Ni-CeO2 catalysts were used as the model catalyst to study the structure-dependent catalytic behavior and catalytic reaction mechanism for hydrogen production from glycerol steam reforming (GSR). Ni/CeO2-HE with the hierarchical structure and ethanol impregnation solvent obtained the strongest metal-support interaction. Electron effects because of the strong interaction between nickel and cerium dioxide promoted the formation of reducible nickel species. High nickel reduction and nickel dispersion contributed to the maximum active nickel exposure surface area, thus Ni/CeO2-HE exhibited superior glycerol conversion than other catalysts. The abundant oxygen vacancies generated due to strong Ni-CeO2 interaction facilitated the dissociation of water, thereby achieving a high yield of H2 for Ni/CeO2-HE. As a comparison, Ni/CeO2 and Ni/CeO2-E showed relatively poor catalytic activity due to lower exposed specific surface area and oxygen vacancy concentration. Moreover, the strong oxygen storage-release ability (CO-OSCC) promoted the oxidation of carbon deposition on Ni/CeO2-HE. As a result, Ni/CeO2-HE obtained good catalytic stability with no inactivation within 25 h. The study of the modulation role of Ni-CeO2 interaction on catalytic behavior can provide valuable guidelines for designing efficient catalysts for GSR.

Source-oriented risk and lung-deposited surface area (LDSA) of ultrafine particles in a Southeast Asia urban area

Submicron and ultrafine particle (UFP) exposure may be epidemiologically and toxicologically linked to pulmonary, neurodegenerative, and cardiovascular diseases. This study explores UFP and fine particle sources using a positive matrix factorization (PMF) model based on PM2.5 chemical compositions and particle number size distributions (PNSDs). The particle chemical composition and size distribution contributions are simultaneously identified to evaluate lung deposition and excess cancer risks. High correlations between the PNSD and chemical composition apportionment results were observed. Fresh and aged traffic particles dominated the number concentrations, while heterogeneous, photochemical reactions and/or regional transport may have resulted in secondary aerosol formation. Fresh and aged road traffic particle sources mostly contributed to the lung deposition dosage in the pulmonary region (~53 %), followed by the tracheobronchial (~30.4 %) and head regions (~16.6 %). However, lung-deposited surface area (LDSA) concentrations were dominated by aged road traffic (~39.2 %) and secondary aerosol (~33.2 %) sources. The excess cancer risks caused by Cr6+, Ni, and As were also mainly contributed to by aged road traffic (~31.7 %) and secondary aerosols (~67 %). The source apportionments based on the physical and chemical properties of aerosol particles are complementary, offering a health impact benchmark of UFPs in a Southeast Asia urban city.

Heterobimetallic CoCeOx derived from cobalt partially-substituted Ce-UiO-66 for chlorobenzene efficient catalytic destruction

Here, a metal–organic framework (MOF)-templated strategy was applied to synthesize the CoCeOx bimetallic catalysts by calcining Co partially-substituted Ce-UiO-66. It is indicated that the substituted Co limited Ce cations in Ce-UiO-66 framework, which affects its growth and structure crystallinity to some extent. After pyrolysis treatment, the derived bimetallic oxide (CoCeOx-M) can basically keep the octahedral structure and the surface area is much higher than the bulk metal composite oxide (CoCeOx-B) prepared by traditional coprecipitation. Results reveal that CoCeOx-M performs the best chlorobenzene degradation capacity, superior stability and vapor tolerance compared with those of CeO2-M (derived from Ce-UiO-66) and CoCeOx-B. At the same time, it is favorable to inhibit the formation of CO during the oxidation reaction. The superior catalytic performance of CoCeOx-M is attributed to a good dispersion of metal cations, high surface area and active oxygen concentration, and good redox property. Moreover, the formation of organic byproducts especially chlorinated organics can be obviously prohibited over CoCeOx-M compared with that of CeO2-M. Mechanism study reveals that chlorobenzene dissociates on the surface of CoCeOx-M to form carboxylates such as acetate species, maleate and phenolate before finally oxidized into CO2, H2O, and HCl. The present work poses new insights into the fabrication of efficient catalysts for industrial CVOC purification.

Effects of Calcium Substitution for La on the Electrochemical Performance of LaMnO3 Nanoparticles

AbstractWith the advantages of short charging and discharging times, high power density, and long cycle life, supercapacitors are regarded as one of the most promising energy storage devices and have garnered massive attention in the field of energy storage. This paper prepared La1−xCaxMnO3 (x=0, 0.05, 0.1, 0.15, and 0.2) nanoparticles by the sol‐gel method. The microstructure, morphology, and electrochemical performance of the samples were characterized. The results depict that La0.85Ca0.15MnO3 has a low charge transfer resistance (0.19 Ω) and a large specific surface area (38.79 m2 g−1). The maximum specific capacitance of the La0.85Ca0.15MnO3 sample reached 248 F/g at a current density of 0.5 A/g, which is ascribable to its large specific surface area and high oxygen vacancy concentration. The anion‐intercalation mechanism was investigated by the charging and discharging process. The above results depict that Ca‐doping significantly enhances the electrochemical performance of LaMnO3 system.

Real-Time Measurement of Personal Exposure to Airborne Nano-Objects with the DiSCminiPart 2 – Application Examples of the DiSCmini/Echtzeitmessung der persönlichen Exposition gegenüber luftgetragenen Nano-Objekten mit dem DiSCminiTeil 2 – Anwendungsbeispiele

The use of the DiSCmini has developed considerably in the context of evaluating inhalation exposure to nanoparticles. This article presents the results obtained during measurement campaigns at workplaces. A few examples describe the applicability of the DiSCmini to measure nano-objects in different metrics complementary to standard exposure measurement methods. This article is the follow up of the instrument’s working principle description and laboratory comparison [1], that showed its ability to determine personal exposure to ultrafine particles and nano-objects in the size range below approximately 700 nm. Besides the number concentration, also the surface area concentration as well as a mean diameter of the aerosol is determined. The DiSCmini is one of the few instruments allowing person mounted use to measure directly the personal exposure to ultrafine particles. For a more comprehensive exposure determination, other instruments can be useful like direct reading instruments for the size range above 700nm, in addition to conventional aerosol samplers for mass concentrations. Although occupational exposure limit values for a number concentration are not in use for ultrafine particles or nano-objects, number based reference values can be chosen for an assessment of the exposure [2]. Such easy to use instruments like the DiSCmini can also be used in a tiered approach for exposure determination of nano-objects as described in a European Standard [3]. The first two phases of the latter approach is a suitable application to get an overview of the concentrations. Another application for such direct reading instruments will be the assessment of protective measures at particle emitting processes, e.g. the application of local exhaust ventilation [4]. Further experience in using the DiSCmini in the laboratory and the field was described in [5, 6, 7], while a review on exposure measurement methods for nano-objects is given in [8]. The following part describes examples of use of the DiSCmini and should help the reader to plan such applications and show which data can be expected.

Homologue-based Estimations of Short-Chain Chlorinated Paraffin Emissions and Concentrations in Japan

Short-chain chlorinated paraffins (SCCPs) are persistent organic pollutants. In Japan, SCCPs are widely detected in the environment although the production and use of SCCPs have been banned. It is essential to estimate the amount and sources of SCCPs to implement countermeasures for SCCP emission. In this study, we estimated the emission and environmental concentrations of SCCP homologues in Japan from 1950 to 2050. Initially, the material flow of total SCCPs was estimated considering the material recycling process. The emission from each process during the entire life cycle of products containing SCCPs was estimated for each homologue. Volatilization factors of long-term-use products were specifically estimated from release factors and surface area, weight, and SCCP concentration of products containing SCCPs. The environmental concentrations were then estimated using the environmental fate model. In the material flow and emission estimation, parameter uncertainties, such as emission factors and SCCP application distribution, were considered, assuming each parameter follows a uniform distribution. The results of emission estimation suggested a decreasing trend of SCCP emission in recent years and continuation of this trend in the future. However, some emissions from long-term-use products may persist. In the future, products that have a long lifetime with closed-loop recycling, such as polyvinyl chloride wire-coating materials, are expected to significantly contribute to atmospheric emission. Moreover, recycled products may contain SCCPs. Based on the estimated concentration, the estimated water and sediment concentrations were within the range of the observed concentrations. Conversely, we could reduce the gap between the estimated and observed atmospheric SCCP concentrations compared with those in previous studies that did not consider the volatilization factor for each SCCP-containing product and material recycling process. However, a difference between the estimated and observed concentrations suggests that some unconsidered emission sources may exist that emit SCCPs into the atmosphere, such as SCCPs as impurities in medium-chain chlorinated paraffins, imported products containing SCCPs, and atmospheric advection from other countries. Hence, it is essential to calculate emissions from sources other than products that intentionally contain SCCPs produced in the past.

Observation-based constraints on modeled aerosol surface area: implications for heterogeneous chemistry

Abstract. Heterogeneous reactions occurring at the surface of atmospheric aerosol particles regulate the production and lifetime of a wide array of atmospheric gases. Aerosol surface area plays a critical role in setting the rate of heterogeneous reactions in the atmosphere. Despite the central role of aerosol surface area, there are few assessments of the accuracy of aerosol surface area concentrations in regional and global models. In this study, we compare aerosol surface area concentrations in the EPA's Community Multiscale Air Quality (CMAQ) model with commensurate observations from the 2011 NASA flight-based DISCOVER-AQ (Deriving Information on Surface Conditions from COlumn and VERtically Resolved Observations Relevant to Air Quality) campaign. The study region includes the Baltimore and Washington, D.C. metropolitan area. Dry aerosol surface area was measured aboard the NASA P-3B aircraft using an ultra-high-sensitivity aerosol spectrometer (UHSAS). We show that modeled and measured dry aerosol surface area, Sa,mod and Sa,meas respectively, are modestly correlated (r2=0.52) and on average agree to within a factor of 2 (Sa,mod/Sa,meas=0.44) over the course of the 13 research flights. We show that Sa,mod/Sa,meas does not depend strongly on photochemical age or the concentration of secondary biogenic aerosol, suggesting that the condensation of low-volatility gas-phase compounds does not strongly affect model–measurement agreement. In comparison, there is strong agreement between measured and modeled aerosol number concentration (Nmod/Nmeas=0.87, r2=0.63). The persistent underestimate of Sa in the model, combined with strong agreement in modeled and measured aerosol number concentrations, suggests that model representation of the size distribution of primary emissions or secondary aerosol formed at the early stages of oxidation may contribute to the observed differences. For reactions occurring on small particles, the rate of heterogeneous reactions is a linear function of both Sa and the reactive uptake coefficient (γ). To assess the importance of uncertainty in modeled Sa for the representation of heterogeneous reactions in models, we compare both the mean and the variance in Sa,mod/Sa,meas to those in γ(N2O5)mod/γ(N2O5)meas. We find that the uncertainty in model representation of heterogeneous reactions is primarily driven by uncertainty in the parametrization of reactive uptake coefficients, although the discrepancy between Sa,mod and Sa,meas is not insignificant. Our analysis suggests that model improvements to aerosol surface area concentrations, in addition to more accurate parameterizations of heterogeneous kinetics, will advance the representation of heterogeneous chemistry in regional models.

Multi-instrument assessment of fine and ultrafine titanium dioxide aerosols

ABSTRACT The measurement of fine (diameter: 100 nanometers–2.5 micrometers) and ultrafine (UF: < 100 nanometers) titanium dioxide (TiO2) particles is instrument dependent. Differences in measurements exist between toxicological and field investigations for the same exposure metric such as mass, number, or surface area because of variations in instruments used, operating parameters, or particle-size measurement ranges. Without appropriate comparison, instrument measurements create a disconnect between toxicological and field investigations for a given exposure metric. Our objective was to compare a variety of instruments including multiple metrics including mass, number, and surface area (SA) concentrations for assessing different concentrations of separately aerosolized fine and UF TiO2 particles. The instruments studied were (1) DustTrak™ DRX, (2) personal DataRAMs™ (PDR), (3) GRIMMTM, and (4) diffusion charger (DC). Two devices of each field-study instrument (DRX, PDR, GRIMM, and DC) were used to measure various metrics while adjusting for gravimetric mass concentrations of fine and UF TiO2 particles in controlled chamber tests. An analysis of variance (ANOVA) was used to apportion the variance to inter-instrument (between different instrument-types), inter-device (within instrument), and intra-device components. Performance of each instrument-device was calculated using root mean squared error compared to reference methods: close-faced cassette and gravimetric analysis for mass and scanning mobility particle sizer (SMPS) real-time monitoring for number and SA concentrations. Generally, inter-instrument variability accounted for the greatest (62.6% or more) source of variance for mass, and SA-based concentrations of fine and UF TiO2 particles. However, higher intra-device variability (53.7%) was observed for number concentrations measurements with fine particles compared to inter-instrument variability (40.8%). Inter-device variance range(0.5–5.5%) was similar for all exposure metrics. DRX performed better in measuring mass closer to gravimetric than PDRs for fine and UF TiO2. Number concentrations measured by GRIMMs and SA measurements by DCs were considerably (40.8–86.9%) different from the reference (SMPS) method for comparable size ranges of fine and UF TiO2. This information may serve to aid in interpreting assessments in risk models, epidemiologic studies, and development of occupational exposure limits, relating to health effect endpoints identified in toxicological studies considering similar instruments evaluated in this study.

Outdoor Microplastic Analysis Using Inlet Filters from an NOx Regulatory Air Quality Monitoring Device

Atmospheric microplastics (MPs) are a ubiquitous environmental contaminant of emerging concern. Sampling methods provide information relating to surface area concentration and MP characteristics, without direct comparison with routinely measured standard air quality parameters. This study analysed 6 active air samples generated by a local authority as part of their routine air quality monitoring activities. Continuous sampling totalled 10 months, within the city centre of Kingston-upon-Hull. By using μFTIR analysis, levels of total particles detected using the NOx inlet filters ranged from 5139 ± 2843 particles m−2 day−1, comprising 1029 ± 594 MPs m−2 day−1. The controls displayed a mean level of 2.00 ± 3.49 MPs. The polymers nylon (32%) and polypropylene, PP (22%) were the most abundant. Small fragments of 47.42 ± 48.57 μm (length) and 21.75 ± 13.62 μm (width) were most common. An increase in MP levels during April 2020 coincided with an increase in PM10 levels. This study used robust procedures to measure MPs in the air by exploiting existing air quality monitoring equipment. Knowing the levels, types, and characteristics of MPs can inform toxicity studies to provide more environmentally relevant exposures, which is urgent now that MPs have been reported in human lung tissue.