Low Concentrations Of NO Research Articles

High-Performance Ppb Level NO2 Gas Sensor Based on Colloidal SnO2 Quantum Wires/Ti3C2Tx MXene Composite.

Nitrogen dioxide is one origin of air pollution from fossil fuels with the potential to cause great harm to human health in low concentrations. Therefore, low-cost, low-power-consumption sensors for low-concentration NO2 detection are essential. Herein, heterojunction by SnO2 quantum wires, a traditional metal oxide NO2 sensing material, and Ti3C2Tx MXene, a novel type of 2D layered material, was synthesized using a simple solvothermal method for enhancing gas-sensing performance and reducing operating temperature. The operating temperature was reduced to 80 °C, with a best performance of 27.8 and a fast response and recovery time (11 s and 23 s, respectively). The SnO2 and Ti3C2Tx MXene composite exhibits high speed and low detection limit due to the construction of the heterojunction with high conductive Ti3C2Tx MXene. The selectivity and stability of gas sensors are carried out. This could enable the realization of fast response, high-sensitivity, and selective NO2 sensing under low operating temperatures.

Photocatalytic NO removal over defective Bi/BiOBr nanoflowers: The inhibition of toxic NO2 intermediate via high humidity

Water vapor (relative humidity) is an ineluctable factor for photocatalytic removal of low-concentration NO in practical environment. In this work, defective Bi/BiOBr nanoflowers were synthesized by a solvothermal approach. Benefiting from bismuth and oxygen vacancies, the efficiency of photocatalytic NO removal increased from the initial 26 % to 63 % when exposed to visible light. Furthermore, photocatalytic NO removal performance at various relative humidity levels was explored. It was found that the NO removal efficiency was negligibly affected by humidity. However, the generation of toxic NO2 intermediate was reduced progressively from 87 to 29 ppb as the humidity increased from 5 % to 100 %, which may be attributed to the high hydrophilicity of NO2. The NO-TPD and in-situ DRIFTS were further employed to unveil the pathway of adsorption and photocatalytic removal of NO. This study discloses a strategy for effectively removing NO from the atmosphere by reducing emission of harmful intermediate NO2.

Enhanced Sub-ppm NO₂-Sensing Properties of SnS₂ Sheet Flowers Decorated With Au Nanoparticles at Near Room Temperature

Tin(IV) sulfide (SnS2) decorated by different levels of Au nanoparticles was successfully prepared by the solvothermal method, followed by in situ reductions. The Au nanoparticles were uniformly coated on the surface of SnS2 sheet flowers. Further gas-sensing test results show that the modified Au nanoparticles greatly enhanced the NO2-sensing performances of SnS2 sheet flowers. In particular, the sensor based on 0.5 wt% Au-SnS2 exhibited a high response of 13.2 toward 2 ppm NO2, which was 10.047-fold higher than that of the pristine SnS2 sensor at near room temperature (60 °C). Meanwhile, it also shows a curtate response and recovery time (45/148 s) and improved selectivity toward NO2 in comparison with pristine SnS2. The enhanced sensing mechanism of composites was probably due to the electronic and chemical sensitization of Au nanoparticles. The sensor based on 0.5 wt% Au-SnS2 presents huge advantages in detecting low-concentration NO2 at near room temperature.

Do neighbourhood traffic-related air pollution and socio-economic status moderate the associations of the neighbourhood physical environment with cognitive function? Findings from the AusDiab study

Characteristics of the neighbourhood environment, including the built and natural environment, area-level socio-economic status (SES) and air pollution, have been linked to cognitive health. However, most studies have focused on single neighbourhood characteristics and have not considered the extent to which the effects of environmental factors may interact. We examined the associations of measures of the neighbourhood built and natural environment, area-level SES and traffic-related air pollution (TRAP) with two cognitive function domains (memory and processing speed), and the extent to which area-level SES and TRAP moderated the associations.We used cross-sectional data from the AusDiab3 study, an Australian cohort study of adults (mean age: 61 years) in 2011–12 (N = 4141) for which geocoded residential addresses were available. Spatial data were used to create composite indices of built environment complexity (population density, intersection density, non-commercial land use mix, commercial land use) and natural environment (parkland and blue spaces). Area-level SES was obtained from national census indices and TRAP was based on estimates of annual average levels of nitrogen dioxide (NO2). Confounder-adjusted generalised additive mixed models were used to estimate the independent associations of the environmental measures with cognitive function and the moderating effects of area-level SES and TRAP. The positive associations between built environment complexity and memory were stronger in those living in areas with higher SES and lower NO2 concentrations. A positive association between the natural environment and memory was found only in those living in areas with lower NO2 concentrations and average or below-average SES. Built environment complexity and the natural environment were positively related to processing speed. Complex urban environments and access to nature may benefit cognitive health in ageing populations. For higher-order cognitive abilities, such as memory, these positive effects may be stronger in areas with lower levels of TRAP.

Room temperature detection of nitrogen dioxide gas sensor based on Pt-modified MoSe2 nanoflowers: Experimental and theoretical analysis

The intrinsic and Pt-doped MoSe2 gas sensing materials with hierarchical flower structure were prepared by hydrothermal routes, and its crystal morphology and chemical element composition were studied by microscopic characterization. The response properties of the MoSe2-based sensors to NO2 were tested by the gas sensing test platform. The test results confirmed that the Pt-doped sample exhibited excellent detection properties for 20 ppm NO2, with a response of 7.29 (3.14 times of the intrinsic MoSe2) at room temperature. The introduction of Pt caused the beneficial specific surface area of MoSe2, and offered more reaction sites for gas-sensitive reactions. In addition, the promotion impact of doped Pt on the adsorption capability of MoSe2 to NO2 was confirmed from the aspects of electronic properties and adsorption behavior based on the density functional theory (DFT). The combination of experimental consequence and theoretical analysis indicates the promising application prospects of the Pt-doped MoSe2 nanoflower for low-concentration NO2 detection at room temperature.

Synthesis and Low-concentration (50 ppm) NO2 Sensing Properties of Bare and ZnO (n) Decorated TeO2 (p) Nanowires

Synthesis and Low-concentration (50 ppm) NO2 Sensing Properties of Bare and ZnO (n) Decorated TeO2 (p) Nanowires

Characteristics of Atmospheric Compounds based on Regional Multicorrelation Analysis in Honam Area

Particulate Matter (PM) in the atmosphere has serious impacts on human health and the global environmental systems. To reduce anthropogenic PM emissions is of importance to protect public health. In this study, the variation of concentrations in PM<sub>2.5</sub>, NO<sub>2</sub>, and O<sub>3</sub> of Honam region over the past 6 years (2016-2021) was investigated. A statistical approach (i.e., hierarchical cluster analysis) was performed to present their spatial relationships. As a result, the high concentration of PM<sub>2.5</sub> in Iksan-si was found in sources of primary pollutants emitted from industrial complexes and ammonia from large-scale livestock complexes. The high concentration periods of PM<sub>2.5</sub> with lower concentrations of NO<sub>2</sub> and O<sub>3</sub> can be seasonal and secondary PM product contributions. In addition, the concentration of O<sub>3</sub> in Buan-gun and Wanju-gun with lower PM levels can be the effect of emission of volatile organic compounds (VOC<sub>S</sub>) from sources. It is necessary to strengthen management for reducing emissions by sources and to establish a policy to control precursors of the atmospheric contaminants.

Density functional theory study on catalytic reduction of NO on semi-coke containing N and Fe: The effect of CO

NOx is a common air pollutant, and its removal research is imminent. In this paper, the semi-coke segment was used as the catalyst carrier to study the three important factors of nitrogen doping, iron doping and CO introduction, and the NO heterogeneous reduction was analyzed by the DFT calculation method. And at the range of 300 to 1000 K, the reaction kinetics was quantitatively analyzed by the conventional transition state theory (TST). Only one NO molecule was needed to finish the whole reaction path by doping the nitrogen, as suggested the nitrogen doping improved the NO removal rate at low NO concentrations. Through the analysis of the adsorption energy, it was found that the adsorption capacity of carbon active sites for NO and CO was significantly enhanced with iron doping. Among them, the appearance of FeO groups also reduced the activation energy of the stage reaction. In addition, the CO introduction significantly promoted the production of N2, CO2 and N2O, which was manifested in the reduction of activation energy of NO catalytic reaction and the increase of the N2 and N2O reaction rate constant. This theoretical research provided a theoretical foundation for the subsequent experimental research on NO removal.

The association between air pollution, meteorological factors, and daily outpatient visits for urticaria in Shijiazhuang, Hebei Province, China: a time series analysis.

The associations of air pollution and meteorological factors with the outpatient visits of urticaria remain poorly studied. This study aimed to assess the association between air pollution, meteorological factors, and daily outpatient visits for urticaria in Shijiazhuang, China, during 2014-2019. Daily recordings of air pollutant concentrations, meteorological data, and outpatient visits data for urticaria were collected during the 6years. Descriptive research methods were used to describe the distribution characteristics and demographic features of urticaria. A combination of the generalized linear regression model (GLM) and distribution lag nonlinear model (DLNM) was used to evaluate the lag association between environmental factors and daily outpatient visits for urticaria. Stratified analyses by gender (male; female) and age (< 18years; 18-39years; > 39years) were further conducted. The dose-response relationship between daily urticaria visits and CO, NO2, O3, temperature, and relative humidity was nonlinear. High concentrations of CO, NO2, O3, and high temperatures increased the risk of urticaria outpatient visits. The maximum cumulative association of high concentrations of CO, NO2, and O3 was lag 0-14days (CO: RR = 1.10, 95%CI: 1.06, 1.31; NO2: RR = 1.09, 95%CI: 1.01, 1.08; O3: RR = 1.16, 95%CI: 1.08, 1.25), and high temperatures was lag 0-7days (RR = 1.27, 95%CI: 1.14, 1.41). Low concentrations of NO2, O3, and high humidity, on the other hand, act as protective factors for urticaria outpatient. The maximum cumulative association of low concentrations of NO2 was the 0-day lag (RR = 0.97, 95%CI: 0.95, 0.99), O3 was lag 0-5days (RR = 0.94, 95%CI: 0.88, 0.99), and high humidity was lag 0-10days (RR = 0.93, 95%CI: 0.89, 0.98). Stratified analyses showed that the risk of urticaria outpatient visits was higher for the males and in the < 18years age group. In conclusion, we found that the development of urticaria in Shijiazhuang has a distinct seasonal and cyclical nature. Air pollutants and meteorological factors had varying degrees of influence on the risk of urticaria outpatient visits. This study provides indirect evidence for a link between air pollution, meteorological factors, and urticaria outpatient visits.

Ni(OH)2 clusters decorated NiTiO3 Z-scheme heterojunctions with strong O2 activation and robust interfacial built-in electric field for efficient NO photo-oxidation

Photocatalytic oxidation offers a viable method for removing low-concentration NO from the atmosphere. However, poor oxygen adsorption-activation capacity and high re-combination rate of electrons and holes limit the photocatalytic NO oxidation activity. To over-come these problems, Ni(OH)2 clusters decorated NiTiO3 Z-scheme heterojunctions are constructed by a precipitation method. The tight interfacial contacts and built-in electric field between the (002) crystal facet of Ni(OH)2 and (012) crystal facet of NiTiO3 promote a Z-scheme charge transfer mechanism. This Z-scheme mechanism will enhance the charge-transfer driving force and result in high separation efficiency of the charges, thus leading to an enhanced photocatalytic performance. Importantly, introducing Ni(OH)2 is considered a promising strategy to enhance the adsorption ability of the O2, NO and NO2. This might help to increase O2 activation efficiency and speed up NO deep oxidation, leading to high NO removal efficiency and low NO2 selectivity. Benefiting from the above excellent properties, the photocatalytic NO oxidation efficiency of Ni(OH)2/NiTiO3 composites is enhanced and the formation of more toxic NO2 is inhibited compared with that of NiTiO3. This work offers a promising and effective route to design efficient NiTiO3-based photocatalysts in the application of environmental remediation.

Effective Absorption Mechanism of SO2 and NO2 in the Flue Gas by Ammonium-Bromide-Based Deep Eutectic Solvents.

Simultaneous capture of SO2 and NOx from flue gas is critical for coal-fired power generation. In this study, environmentally friendly and high-performance deep eutectic solvents based on ethylene glycol and ammonium bromide were designed to capture SO2 and NO2 simultaneously. The SO2 and NO2 absorption performances and absorption mechanisms were systematically investigated by 1H NMR and Fourier transform infrared (FT-IR) spectroscopy in combination with ab initio calculations using Gaussian software. The results showed that EG-TBAB DESs can absorb low concentrations of SO2 and NO2 from the flue gas simultaneously at low temperatures (≤50 °C). 1H NMR, FT-IR, and simulation results indicate that SO2 and NO2 are absorbed by forming EG-TBAB-SO2–NO2 complexes, Br– is the main active site for NO2 absorption, and NO2 is more active in an EG-TBAB-NO2–SO2 complex than SO2. EG-TBAB DESs exhibit outstanding regeneration capability, and absorption capacities remain unchanged after five absorption–desorption cycles. The fundamental understanding of simultaneous capture of SO2 and NO2 from this study enables DES structures to be rationally designed for efficient and low-cost desulfurization and denitrification reagents.

Stability and characteristics of NH3/CH4/air flames in a combustor fired by a double swirl stabilized burner

Compared to hydrocarbons, ammonia's low reactivity and higher NOx emissions limit its practical application. Consequently, its implementation in combustion systems requires a different combustor geometry, by adapting existing systems or developing new ones. This study investigates the flame stability, NO emissions, and flame structure of NH3/CH4/air premixed flames in a novel combustor comprising a double swirl burner. A lean premixed CH4/air mixture of equivalence ratio, Φout, was supplied to the outer swirl, while a NH3/CH4/Air mixture fed the inner swirl. The molar fraction of NH3 in the inner fuel blend, xNH3, was varied from 0 (pure CH4) to 1 (pure NH3) over far-lean to far-rich inner stream equivalence ratio, Φin. This new burner's stability map was established in terms of Φin versus xNH3 for different Φout. Then, NO emissions were measured versus Φin for various xNH3 and Φout. Finally, based on the NO emissions, eight flames were down-selected for in-flame measurements, which included temperature and OH-PLIF. The stability measurements revealed that increasing xNH3 modifies the stability map by increasing the lean blowout limits and narrowing the flashback region. At Φout ≥ 0.6, a stable flame was achieved for a pure inner NH3/air mixture. Low NO emissions were achieved in this burner configuration at xNH3=1 by either enriching or far-leaning Φin. Enriching Φin led to a steep decrease in NO concentrations. However, to achieve low NO concentrations, precise control of Φout was needed. At Φin=1.4, 220 ppm NO at Φout=0.7 versus 690 at Φout=0.6 was measured. Moreover, substantially enriching Φin>1.2 led to a slight decrease in measured NO. Generally, the OH-PLIF images revealed a conical OH-layer at the burner exit. Certain flame conditions created OH-pockets inside the conical structure or formed a V-shaped OH-layer far downstream. This change in flame structure was found to impact NO emissions strongly.

Vertical profiles of O3, NO2 and PM in a major fine chemical industry park in the Yangtze River Delta of China detected by a sensor package on an unmanned aerial vehicle

The vertical profiles and diurnal variations of air pollutants at different heights in the fine chemical industry park (FCIP) were systematically studied in this study. Air pollutants in a major FCIP in the Yangtze River Delta of China within 500 m above ground level (AGL) detected by a sensor package on an unmanned aerial vehicle (UAV). The air pollutants including ozone (O3), nitrogen dioxide (NO2), particulate matter (PM), total volatile organic compounds (TVOCs) and carbon monoxide (CO), respectively, had been measured through more than one hundred times of vertical flights from Aug. 2020 to Jul. 2021. The concentrations of NO2 and CO generally decreased with the height while the concentrations of O3 increased with the height within 500 m AGL. The photochemical reaction resulted in a strong inverse relationship between the vertical profiles of O3 and that of NO2. The concentrations of PM2.5 and TVOCs generally decreased with the height below 100 m AGL and were fully mixed above 100 m AGL. The vertical profiles of different particle sizes were well consistent with the R2 value of 0.97 between PM1 and PM2.5 and 0.93 between PM2.5 and PM10. The NO2 and PM2.5 concentrations sometimes increased with height maybe due to the influence of temperature inversion layer or long-distance transportation from northern China. The diurnal variations of NO2, O3, TVOCs and CO concentrations at different heights within 500 m AGL were basically consistent. The diurnal variations range of PM2.5 concentrations below 100 m AGL was large and different from other heights, which should be greatly influenced by the local emissions. The unstable atmospheric stability was accompanied by strong photochemical reactions and convective activities, resulting in low concentrations of NO2 and PM2.5, while high concentrations of O3.

Heterostructures Based on Cobalt Phthalocyanine Films Decorated with Gold Nanoparticles for the Detection of Low Concentrations of Ammonia and Nitric Oxide.

This work is aimed at the development of new heterostructures based on cobalt phthalocyanines (CoPc) and gold nanoparticles (AuNPs), and the evaluation of the prospects of their use to determine low concentrations of ammonia and nitric oxide. For this purpose, CoPc films were decorated with AuNPs by gas-phase methods (MOCVD and PVD) and drop-casting (DC), and their chemiresistive sensor response to low concentrations of NO (10–50 ppb) and NH3 (1–10 ppm) was investigated. A comparative analysis of the characteristics of heterostructures depending on the preparation methods was carried out. The composition, structure, and morphology of the resulting hybrid films were studied by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma atomic emission (ICP-AES) spectroscopy, as well as electron microscopy methods to discuss the effect of these parameters on the sensor response of hybrid films to ammonia and nitric oxide. It was shown that regardless of the fabrication method, the response of Au/CoPc heterostructures to NH3 and NO gases increased with an increase in the concentration of gold. The sensor response of Au/CoPc heterostructures to NH3 increased 2–3.3 times compared to CoPc film, whereas in the case of NO it increased up to 16 times. The detection limits of the Au/CoPc heterostructure with a gold content of ca. 2.1 µg/cm2 for NH3 and NO were 0.1 ppm and 4 ppb, respectively. It was shown that Au/CoPc heterostructures can be used for the detection of NH3 in a gas mixture simulating exhaled air (N2—74%, O2—16%, H2O—6%, CO2—4%).

Plasma reforming for enhanced ammonia-air ignition: A numerical study

Using an in-house 0D plasma chemical solver, this paper investigates the species involved in plasma-assisted reforming of both pure ammonia and stoichiometric ammonia-air mixtures. A nanosecond repetitively pulsed plasma is simulated for dielectric barrier discharge conditions, with reduced electric fields of 180 and 360 Td, energies per pulse of 0.5 and 1 mJ/cm3, and pulse repetition frequencies up to 500 kHz. To show the effect of reforming on combustion performance, the reformates are fed into a neutral species combustion chemistry solver to calculate the ignition delay time at gas-turbine relevant conditions. For a reformed stoichiometric mixture, it is possible to achieve a reduction of two orders of magnitude in ignition delay time. This reduction, however, comes at the cost of lost enthalpy, as ammonia reacts with oxygen to create water. Path flux and sensitivity analyses were performed, and it as found that the two most crucial species in the reformate were H2 and NH2. The presence of NH2 in high concentration also resulted in lower concentrations of NO after ignition, compared to the unreformed mixture. When reforming pure ammonia, the same number of pulses and energy as in the stoichiometric case reduce ignition by one order of magnitude. A higher reduction is possible with more pulses, unlike the stoichiometric reforming case in which ignition is reached during the reforming process, and with no loss of enthalpy due to oxidation. At 200 kHz, a reduction of two orders of magnitude is possible after 1500 pulses. These results support the feasibility of plasma-assisted reforming for the improvement of ammonia combustion characteristics at relevant conditions.

OH and HO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; radical chemistry at a suburban site during the EXPLORE-YRD campaign in 2018

Abstract. The first OH and HO2 radical observation in Yangtze River Delta, one of the four major urban agglomerations in China, was carried out at a suburban site (Taizhou) in summer 2018 from May to June, aiming to elucidate the atmospheric oxidation capacity in this region. The maximum diurnal averaged OH and HO2 concentrations were 1.0×107 and 1.1×109 cm−3, respectively, which were the second highest HOx (sum of OH and HO2) radical concentrations observed in China. HONO photolysis was the dominant radical primary source, accounting for 42 % of the total radical initiation rate. Other contributions were from carbonyl photolysis (including HCHO, 24 %), O3 photolysis (17 %), alkene ozonolysis (14 %), and NO3 oxidation (3 %). A chemical box model based on the RACM2-LIM1 mechanism could generally reproduce the observed HOx radicals, but systematic discrepancy remained in the afternoon for the OH radical, when the NO mixing ratio was less than 0.3 ppb. An additional recycling mechanism equivalent to 100 ppt NO was capable to fill the gap. The sum of monoterpenes was on average up to 0.4 ppb during daytime, which was all allocated to α-pinene in the base model. A sensitivity test without monoterpene input showed the modeled OH and HO2 concentrations would increase by 7 % and 4 %, respectively, but modeled RO2 concentration would significantly decrease by 23 %, indicating that monoterpene was an important precursor of RO2 radicals in this study. Consequently, the daily integrated net ozone production would reduce by 6.3 ppb without monoterpene input, proving the significant role of monoterpene in the photochemical O3 production in this study. In addition, the generally good agreement between observed and modeled HOx concentrations suggested no significant HO2 heterogeneous uptake process during this campaign. Incorporation of HO2 heterogeneous uptake process would worsen the agreement between HOx radical observation and simulation, and the discrepancy would be beyond the combined measurement–model uncertainties using an effective uptake coefficient of 0.2. Finally, the ozone production efficiency (OPE) was only 1.7 in this study, a few folds lower than other studies in (sub)urban environments. The low OPE indicated a slow radical propagation rate and short chain length. As a consequence, ozone formation was suppressed by the low NO concentration in this study.

Multifunctional Sensors Based on Doped Indium Oxide Nanocrystals.

There is an increasing need for multifunctional sensors that can detect radiation, biological activity, gas, etc. for efficient health monitoring, neurological medical devices, and human-machine interfaces in recent years. Herein, we demonstrated a multifunctional Sn-doped In2O3 nanocrystal (ITO NC) based device for ulyoutraviolet (UV)/infrared (IR) dual-band photodetection and light-activated efficient nitrogen dioxide (NO2) gas sensing at room temperature (RT). The effects of different surface ligands and annealing process of ITO NCs on their photodetection performance were investigated. The ITO NCs capped with 1,2-ethanedithiol (EDT) show a responsivity of 31.3/177.7 mA W-1 and normalized detectivity of ∼1 × 1010/109 cm Hz1/2 W-1 under UV/IR illumination at 375/2200 nm at RT. The potential of the ITO NCs sensors to monitor low concentrations of NO2 is activated by light illumination. The sensor has a higher response (4.2) to 1 ppm of NO2, shorter response/recovery time (156.8/554.2 s), and a lower detection limit (LOD) (219 ppb) under UV illumination compared within a dark environment. The LOD of the sensor is lower than the allowable exposure limit of NO2 specified in "Air Pollutant Limits" of the Occupational Safety and Health Administration (OSHA). Our work paves an alternative platform for the development of low-cost, integration-friendly multifunctional devices.

The excellent photocatalytic NO removal performance relates to the synergistic effect between the prepositive NaOH solution and the g-C3N4 photocatalysis

Photocatalysis technology is used to remove the low concentration NO in recent years. However, the effect of this process is not very satisfactory. In this study, it was found that the prepositive NaOH solution could significantly improve the photocatalytic NO removal activity of g-C3N4. The apparent quantum yield of g-C3N4 in the NO removal process was increased 3.5 times by the prepositive NaOH solution. The reason is that there was a synergistic effect formed between the prepositive NaOH solution and the photocatalytic NO removal process. The prepositive NaOH solution not only could increase the humidity and pH value in the photocatalytic unit, but also could improve the adsorption ability of g-C3N4 for the H2O, NO, and O2. Moreover, the prepositive NaOH solution reduced the difficulty of the photogenerated carriers’ transport and the ·OH generation. This study provided a new idea for the removal of low-concentration NOx.

Design of thin-film configuration of SnO2–Ag2O composites for NO2 gas-sensing applications

Abstract In this study, a two-layered thin-film structure consisting of a dispersed nanoscaled Ag2O phase and SnO2 layer (SA) and a mono-composite film layer (CSA) consisting of a nanoscale Ag2O phase in the SnO2 matrix are designed and fabricated for NO2 gas sensor applications. Two-layered and mono-layered SnO2–Ag2O composite thin films were synthesized using two-step SnO2 and Ag2O sputtering processes and Ag2O/SnO2 co-sputtering approach, respectively. In NO2 gas-sensing measurement results, both SA and CSA thin films that functionalized with an appropriate Ag2O content exhibit enhanced gas-sensing responses toward low-concentration NO2 gas in comparison with that of pristine SnO2 thin film. In particular, a gas sensor made from the mono-composite SnO2–Ag2O layer demonstrates apparently higher NO2 gas-sensing performance than that of double-layered SnO2–Ag2O thin-film sensor. This is attributed to substantially numerous p–n junctions of Ag2O/SnO2 formed in the top region of the SnO2 matrix. The gas-sensing response of the optimal sample (CSA270) toward 10 ppm NO2 gas is 5.91, and the response/recovery speeds in a single cycle dynamic response plot are 28 s/168 s toward 10 ppm NO2, respectively. Such a p–n thin-film configuration is beneficial to induce large electric resistance variation before and after the introduction of NO2 target gas during gas-sensing tests. The experimental results herein demonstrate that the gas-sensing performance of p–n oxide composite thin films can be tuned via the appropriate design of composite thin-film configuration.

Traffic-related NO2 affects expression of Cupressus sempervirens L. pollen allergens.

Traffic pollution has been recognized as directly worsening respiratory symptoms of allergic subjects, although whether urban air pollutants can also directly increase the allergenic potential of pollen has not yet been definitely proven. Therefore, the hypothesis that intra-urban air NO2 variation influences allergens expression in Cupressus sempervirens (Cs) L. pollen was tested. Mature microsporophylls were cut from Cs trees of similar age and height (14-17 m) present in three different sites of Florence (Italy) and processed in the laboratory. Cs pollen allergens amount was determined by a semi-quantitative analysis of electrophoretically separated pollen extracts fractions. NO2 air concentrations were recorded by air monitoring stations located at a distance not exceeding 50 m from each pollen collection site, and the relative annual mean values were acquired by a publicly available database (Tuscan Regional Agency for Environment Protection). Expression of three major Cs pollen allergens was non-linearly correlated with mean annual NO2 concentrations. Expression peak of all major allergens considered was reached at NO2 air concentration (67μg/m3), far below the value at risk for direct effect on the respiratory health (European Union Directive 2008/50/EC). The findings suggest that intra-urban NO2 variations do affect the expression of Cs pollen major allergens, and an apparent low risk NO2 concentration should be regarded as indirectly harmful for increasing the allergenic potential of pollen.