The catalytic oxidation of nitrogen oxide( NO) from waste gas was investigated using advanced oxidation process based on sulfate radicals. The manganese oxide immobilized on graphene oxide( GO) can activate peroxymono...The catalytic oxidation of nitrogen oxide( NO) from waste gas was investigated using advanced oxidation process based on sulfate radicals. The manganese oxide immobilized on graphene oxide( GO) can activate peroxymonosulfate( PMS) for the oxidation of NO in waste gas. The Mn3O4 / GO catalyst system was characterized via X-ray diffraction( XRD), Fourier transform infrared spectrocopy( FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy( XPS), energy dispersive X-ray spectroscopy( EDS),and scanning electron microscope( SEM).The results showed that Mn3O4 was distributed on GO. The Mn3O4 /GO catalyst system exhibited efficient activity for NO oxidation when the Mn3O4 /GO catalyst had an optimum Mn3O4 loading. In addition,the best catalytic oxidation could be achieved within 60 min with 0. 25 mmol /L Mn3 O4 /GO catalyst, and2 mmol /L PMS dosage at 25 ℃. The catalysts also exhibited stable performance after several rounds of regeneration. Therefore,the results may have significant technical implication for utilizing Mn3O4 /PMS to oxidize NO for offgas treatment.展开更多
Based on observational data of ozone(O3) and nitrogen oxide(NOx) mixing ratios on the ground and at high altitude in urban areas of Beijing during a period of six days in November 2011,the temporal and spatial charact...Based on observational data of ozone(O3) and nitrogen oxide(NOx) mixing ratios on the ground and at high altitude in urban areas of Beijing during a period of six days in November 2011,the temporal and spatial characteristics of mixing ratios were analyzed.The major findings include:urban O3 mixing ratios are low and NOx mixing ratios are always high near the road in November.Vertical variations of the gases are significantly different in and above the planetary boundary layer.The mixing ratio of O3 is negatively correlated with that of NOx and they are positively correlated with air temperature,which is the main factor directly causing vertical variation of O3 and NOx mixing ratios at 600-2100m altitude.The NOx mixing ratios elevated during the heating period,while the O3 mixing ratios decreased:these phenomena are more significant at high altitudes compared to lower altitudes.During November,air masses in the urban areas of Beijing are brought by northwesterly winds,which transport O3 and NOx at low mixing ratios.Due to Beijing's natural geographical location,northwest air currents are beneficial to the dilution and dispersion of pollutants,which can result in lower O3 and NOx background values in the Beijing urban area.展开更多
The resonance-enhanced multiphoton ionization (REMPI) spectrum of NO has been obtained. The spectral lines can be attributed to NO D2∑←X2П transitions. NO molecules are ionized via the resonant intermediate D2∑ st...The resonance-enhanced multiphoton ionization (REMPI) spectrum of NO has been obtained. The spectral lines can be attributed to NO D2∑←X2П transitions. NO molecules are ionized via the resonant intermediate D2∑ states and by (3+2) REMPI process.展开更多
The emission of NOx during coal combustion contributes to the formation of acid rain and photochemical smog,which would seriously affect the quality of atmospheric environment.Therefore,the decrease of NOx is of great...The emission of NOx during coal combustion contributes to the formation of acid rain and photochemical smog,which would seriously affect the quality of atmospheric environment.Therefore,the decrease of NOx is of great importance for improving the efficient utilization of coal.The present review comprehensively summarized the influence factors and mechanisms of migration and transformation of nitrogen during the coal pyrolysis and combustion based on experimental study and quantum chemical calculation.Firstly,in the process of pyrolysis:the occurrence state and transformation of nitrogen were concluded.The influence of temperature,atmosphere,heating rate and catalyst on formation of NOx precursor and nitrogen migration path at the molecular level were summarized;Secondly,during the process of combustion:the influence of temperature,ambient oxygen concentration,physical structure of coal char,catalyst on heterogeneous oxidation of char(N)were summarized;The effects of char surface properties,catalyst and ambient atmosphere on heterogeneous reduction of NOx were also concluded.Based on the quantum chemical calculation,the reaction path of heterogeneous oxidation of char-N and heterogeneous reduction of NOx were described in detail.Current studies focus more on the generation of HCN and NH3,but in order to reduce the pollution of NOx from the source,it is necessary to further improve the process conditions and the optimal formula of producing more N2 during pyrolysis,as well as clarify the path of the generation of N2.Experiments study and quantum chemistry calculation should be combined to complete the research of directional nitrogen reduction during pyrolysis and denitration during combustion.展开更多
The gas-phase conversion of U3O8, MoO3, SrO, and their mechanical mixtures, and also of ZrO2 into water-soluble compounds in the atmosphere of (NOx + vapor H2O) or HNO3 (vapor) was studied. In the course of gas-phase ...The gas-phase conversion of U3O8, MoO3, SrO, and their mechanical mixtures, and also of ZrO2 into water-soluble compounds in the atmosphere of (NOx + vapor H2O) or HNO3 (vapor) was studied. In the course of gas-phase conversion, U3O8 and SrO transform into water-soluble compounds (nitrates, hydroxonitrates), whereas MoO3 and ZrO2 undergo no changes. The principal possibility of separating U from Mo and Zr by gas-phase conversion of the oxides in the atmosphere of (NOx + vapor H2O) or HNO3 (vapor) was demonstrated.展开更多
Lightning-generated nitrogen oxides(LNO_(x))have a major influence on the atmosphere and global climate change.Therefore,it is of great importance to obtain a more accurate estimation of LNO_(x).The aim of this study ...Lightning-generated nitrogen oxides(LNO_(x))have a major influence on the atmosphere and global climate change.Therefore,it is of great importance to obtain a more accurate estimation of LNO_(x).The aim of this study is to provide a reference for the accurate estimation of the total LNO_(x) in the mainland of China based on cloud-to-ground lightning(CG)location data from 2014 to 2018.The energy of each CG flash was based on the number of return strokes per CG flash,the peak current of each return stroke,and the assumed CG breakdown voltage.The energy of intracloud lightning(IC)was based on the estimated frequencies of IC and the assumed energy of each IC flash.Combining the energy of lightning and the number of nitric oxide(NO)molecules produced by unit energy(ρno),the total LNO_(x) production in the mainland of China was determined.The LNO_(x) in the mainland of China estimated in this study is in the range(0.157-0.321)×10^(9) kg per year[Tg(N)yr-1],which is on the high end of other scholars’works.Negative cloud-to-ground lightning(NCG)flashes produce the most moles of NO_(x),while positive cloud-to-ground lightning(PCG)flashes produce the least total moles of NO_(x).The breakdown voltage of PCG is greater than that of IC or NCG,while the latter has a greater output of LNO_(x).展开更多
Burning coal briquettes or biomass pellets in household decoupling stoves is of significance to the reduction of residential pollutant emissions such as NO and CO. In order to make full use of the superiority of decou...Burning coal briquettes or biomass pellets in household decoupling stoves is of significance to the reduction of residential pollutant emissions such as NO and CO. In order to make full use of the superiority of decoupling combustion technology, the household stoves should be specially designed and optimized to adapt to fuel types and combustion characteristics. Using numerical simulation and experimental validation, this study quantitatively clarified that the reducibility of devolatilization char plays an important role in the suppression of NO emission in the decoupling combustion of coal, while the reducibility of pyrolysis gases has a dominant effect on the reduction of NO in the decoupling combustion of biomass. An optimal parameter combination of throat height and grate angle was obtained for the simultaneous suppression of NO and CO emissions in the household decoupling stove burning coal briquettes. Two types of decoupling stoves were developed to enable the clean combustion of biomass pellets. The A-type biomass stove with a multi-pass smoke tunnel shows a better comprehensive NO and CO reduction effectiveness than the B-type biomass stove consisting of a two-stage grate structure and an S-shaped pyrolysis chamber. The optimal structural parameters provided references for the design and manufacture of commercial decoupling coal and biomass stoves.展开更多
To meet the emission standard of nitrogen oxides(NOx)in the flue gas of batch furnaces through dry adsorption,a calcium-silica inorganic adsorbent was prepared with limestone and quartz as raw materials.Sample Cu-BTC ...To meet the emission standard of nitrogen oxides(NOx)in the flue gas of batch furnaces through dry adsorption,a calcium-silica inorganic adsorbent was prepared with limestone and quartz as raw materials.Sample Cu-BTC 1#was obtained by solvothermal synthesis,drying and purification in vacuum at 120℃using trimesic acid(H3BTC)and copper nitrate trihydrate(Cu(NO_(3))2·3H_(2)O)as raw materials;likewise,sample Cu-BTC 3#was obtained at 200℃.Sample Cu-BTC 2#was obtained by hydrothermal synthesis,drying and purification in air(metal-organic frameworks,1,3,5-benzene tricarboxylic acid copper).The two types of materials were tested in terms of the NO_(2) adsorption,and then the specific surface area,pore volume,NO_(2) adsorption performance,phase composition,microstructure and thermal stability of the adsorbent materials were exploredvia N_(2) physical adsorption-desorption,SEM,XRD and TG characterization.The results show that:(1)the Cu-BTC samples have higher adsorption capacity than the calcium-silica adsorbent,in which sample Cu-BTC 3#has the largest specific surface area and pore volume,thus adsorption capacity for NO_(2);(2)the calcium-silica adsorbent has better thermal stability and lower total mass loss during the entire process than the Cu-BTC samples;sample Cu-BTC 2#has the best thermal stability among the three Cu-BTC samples,and the metal Cu active sites of the Cu-BTC samples can be exposed at least above 150℃.展开更多
Ammonia (NH<sub>3</sub>) dissociation and oxidation in a cylindrical quartz reactor has been experimentally studied for various inlet NH<sub>3</sub> concentrations (5%, 10%, and 15%) and reacto...Ammonia (NH<sub>3</sub>) dissociation and oxidation in a cylindrical quartz reactor has been experimentally studied for various inlet NH<sub>3</sub> concentrations (5%, 10%, and 15%) and reactor temperatures between 700 K and 1000 K. The thermal effects during both NH<sub>3</sub> dissociation (endothermic) and oxidation (exothermic) were observed using a bundle of thermocouples positioned along the central axis of the quartz reactor, while the corresponding NH<sub>3</sub> conversions and nitrogen oxides emissions were determined by analysing the gas composition of the reactor exit stream. A stronger endothermic effect, as indicated by a greater temperature drop during NH<sub>3</sub> dissociation, was observed as the NH<sub>3</sub> feed concentration and reactor temperature increased. During NH<sub>3</sub> oxidation, a predominantly greater exothermic effect with increasing NH<sub>3</sub> feed concentration and reactor temperature was also evident;however, it was apparent that NH<sub>3</sub> dissociation occurred near the reactor inlet, preceding the downstream NH<sub>3</sub> and H<sub>2</sub> oxidation. For both NH<sub>3</sub> dissociation and oxidation, NH<sub>3</sub> conversion increased with increasing temperature and decreasing initial NH<sub>3</sub> concentration. Significant levels of NO<sub>X</sub> emissions were observed during NH<sub>3</sub> oxidation, which increased with increasing temperature. From the experimental results, it is speculated that the stainless-steel in the thermocouple bundle may have catalysed NH<sub>3</sub> dissociation and thus changed the reaction chemistry during NH<sub>3</sub> oxidation.展开更多
The direct oxidation of nitrogen is a potential pathway to achieving the zero-carbon-emission synthesis of nitric acid or nitrate, because it does not involve ammonia synthesis and additional ammonia oxidation process...The direct oxidation of nitrogen is a potential pathway to achieving the zero-carbon-emission synthesis of nitric acid or nitrate, because it does not involve ammonia synthesis and additional ammonia oxidation processes. However, the slow kinetics of nitrogen oxidation and the difficult selective control of oxidation products hinder the development of this process. In this study, a plasma-driven gas-liquid relay reaction system was developed to overcome these limitations. A typical feature of this reaction system is that it can efficiently generate NO_x under plasma exposure;moreover, the specific anions in the absorption solution can be oxidized to strong oxidants capable of relay oxidation of low-valence nitrogen oxides. This feature allows for the deep oxidation of nitrogen, thus enabling the oxidation products of nitrogen to exist in high-valence states in the absorption solution. For experimental verification, we achieved the 100% selective synthesis of nitrate under plasma exposure, with air as the supply gas and a sodium sulfate solution as the absorption solution.展开更多
The effects of NOx(in a ratio of NO∶NO2=9∶1) and SO2in cathode streamonthe performance of a single proton ex-change membrane fuel cell(PEMFC) were investigated.NOxwith concentrations of 1×10-3%(in volume,the sa...The effects of NOx(in a ratio of NO∶NO2=9∶1) and SO2in cathode streamonthe performance of a single proton ex-change membrane fuel cell(PEMFC) were investigated.NOxwith concentrations of 1×10-3%(in volume,the same as fol-lows),1.4×10-2%and 1×10-3%could cause significant detri mental effects on the cell performance.However,nearly com-plete recovery of the cell performance could be observed after NOxwas shut off and purged with clean air.The electrochemicalmeasurements suggested that thei mpacts of NOxresulted mainlyfromthe superposition of the oxygen reduction reaction(ORR),NOand HNO2oxidation reactions,and the increased cathodic i mpedance.Trace SO2with concentrations of 5×10-6%,5×10-3%,2×10-4%and 3.2×10-4%influenced the cell muchseverer,which could be attributed toits strong adsorption onthesurface of Pt atoms.The cell performance could not be completely recovered after purged with clean air and cyclic voltammetry(CV) tests,due to the changes of electrochemical i mpedance spectroscopy(EIS) and electrochemical active surface(EAS) causedby surface state change after SO2exposure.展开更多
Emissions of exhaust gases and particulate matter from a dual fuel marine engine using methanol as fuel with marine gasoil as pilot fuel have been examined for a ferry during operation.The emission factor for nitrogen...Emissions of exhaust gases and particulate matter from a dual fuel marine engine using methanol as fuel with marine gasoil as pilot fuel have been examined for a ferry during operation.The emission factor for nitrogen oxides is lower than what is typically found for marine gasoil but does not reach the tier III limit.The emissions of particulate matter are significantly lower than for fuel oils and similar to what is found for LNG engines.The main part of the particles can be found in the ultrafine range with the peak being at around 18 nm.About 93%of the particles are evaporated and absorbed when using a thermodenuder,and thus a large majority of the particles are volatile.Methanol is a potential future marine fuel that will reduce emissions of air pollutants and can be made as a biofuel to meet emission targets for greenhouse gases.展开更多
In this study,a model is developed to simulate the dynamics of an internal combustion engine,and it is calibrated and validated against reliable experimental data,making it a tool that can effectively be adopted to co...In this study,a model is developed to simulate the dynamics of an internal combustion engine,and it is calibrated and validated against reliable experimental data,making it a tool that can effectively be adopted to conduct emission predictions.In this work,the Ricardo WAVE software is applied to the simulation of a particular marine diesel engine,a four-stroke engine used in the maritime field.Results from the bench tests are used for the calibration of the model.Finally,the calibration of the model and its validation with full-scale data measured at sea are presented.The prediction includes not only the classic engine operating parameters for a comparison with surveys but also an estimate of nitrogen oxide emissions,which are compared with similar results obtained with emission factors.The calibration of the model made it possible to obtain an overlap between the simulation results and real data with an average error of approximately 7%on power,torque,and consumption.The model provides encouraging results,suggesting further applications,such as in the study on transient conditions,coupling of the engine model with the ship model for a complete simulation of the operating conditions,and optimization studies on consumption and emissions.The availability of the emission data during the sea trial and validated simulation results are the strengths and novelties of this work.展开更多
This work examines the effect of butanol as an oxygenated additive to lower carbon monoxide,smoke,nitrogen oxide and hydrocarbon emissions and to improve the performance aspects of Calophyllum inophyllum(Punnai)biodie...This work examines the effect of butanol as an oxygenated additive to lower carbon monoxide,smoke,nitrogen oxide and hydrocarbon emissions and to improve the performance aspects of Calophyllum inophyllum(Punnai)biodiesel.Singlecylinder,oil-cooled compression ignition engines are employed in this work.Neat Punnai biodiesel(P100)is blended with butanol at 10%and 20%by volume and labelled as B10 P90 and B20 P80,respectively.Methanol and alkaline catalyst(KOH)were used for the transesterification process for biodiesel production.The transesterification technique yielded 88%biodiesel from raw Punnai oil.Engine tests resulted in lower CO,smoke,NO_x and HC emissions when fuelled with both butanol blends when compared to P100.In addition,BSFC(brake-specific fuel consumption)reduced and BTE(brake thermal effciency)increased with the inclusion of butanol blends(B10 and B20)to neat Punnai biodiesel.展开更多
BACKGROUND Type 1 diabetes originates from gene-environment interactions,with increasing incidence over time.AIM To identify correlates of childhood type 1 diabetes in European countries using an ecological approach.S...BACKGROUND Type 1 diabetes originates from gene-environment interactions,with increasing incidence over time.AIM To identify correlates of childhood type 1 diabetes in European countries using an ecological approach.Several environmental variables potentially influencing the onset of type 1 diabetes have been previously evaluated.However,the relationships between epidemiologic data and exposure to toxic airborne molecules are scarcely studied.METHODS We employed an ecological model to explore,in a wide time period(1990-2018),associations between type 1 diabetes incidence in 19 European countries(systematic literature review)and the nationwide production of five widely diffused air pollutants:particulate matter<10μm(PM10),nitrogen oxides(NO),non-methane volatile organic compounds(VOCs),sulphur oxide(SO2),and ammonia.RESULTS Data confirm a raising incidence of type 1 diabetes in 18 out of 19 explored countries.The average difference(last vs first report,all countries)was+6.9×100000/year,with values ranging from-1.4(Germany)to+16.6(Sweden)per 100000/year.Although the overall production of pollutants decreased progressively from 1990 to 2018,type 1 diabetes incidence was positively associated with the nationwide emissions of PM10,VOCs,and NO but not with those of SO2 and ammonia.Type 1 diabetes incidence was significantly higher in countries with high emissions than in those with low emissions of PM10(27.5±2.4 vs 14.6±2.4×100000 residents,respectively),VOCs(24.5±4.4 vs 13.2±1.7×100000 residents,respectively),and NO(26.6±3 vs 13.4±2.4×100000 residents,respectively),but not of SO2 or ammonia.CONCLUSION Evidence justify further studies to explore better links between long-term air quality and type 1 diabetes onset at the individual level,which should include exposures during pregnancy.In this respect,type 1 diabetes could be,at least in part,a preventable condition.Thus,primary prevention policies acting through a marked abatement of pollutant emissions might attenuate future type 1 diabetes incidence throughout Europe.展开更多
In this paper,removal of nitrogen oxide(NO) is investigated in capacitive atmospheric pressure discharges driven by both radio-frequency(RF) and trapezoidal pulsed power with a onedimensional self-consistent fluid mod...In this paper,removal of nitrogen oxide(NO) is investigated in capacitive atmospheric pressure discharges driven by both radio-frequency(RF) and trapezoidal pulsed power with a onedimensional self-consistent fluid model.The results show that the number density of NO could be reduced significantly once a short pulse of low duty ratio is additionally applied to the RF power.It is found that the process of NO removal by the pulse-modulated RF discharge could be divided into three stages:the quick reaction stage,the NO removal stage,and the sustaining stage.Furthermore,the temporal evolution of particle densities is analyzed,and the key reactions in each stage are discovered.Finally,the influence on the removal efficiency of the voltage amplitude of the pulse and the RF voltage amplitude is investigated.展开更多
In the present study reduction of nitrogen oxides using reburning technology, during combustion of sewage sludge (fuel I) and the mixture of sewage sludge, wasted bleaching earth and CaO (fuel II), was carried out. Th...In the present study reduction of nitrogen oxides using reburning technology, during combustion of sewage sludge (fuel I) and the mixture of sewage sludge, wasted bleaching earth and CaO (fuel II), was carried out. The experimental works were conducted in a laboratory-scale fluidized bed reactor (power up to 10 kW) with application of two types of beds: chemically inert bed (sand) and chemically active bed (CaO). The second combustion (reburning) zone in the reactor was formed by dosing into an area above the bed, additional gaseous fuel (propane). Obtained reduction in emissions of nitrogen oxides in both types of beds was at a level 70% - 79%. Additionally bed of CaO has the desulfurizing effect and also reduces the CO concentration in the exhaust fumes. A significant drawback of active bed is the adverse effect on increase of the primary NO which enters the second combustion zone. The result of this fact is higher NOx emission during combustion of the same fuel in bed of CaO in comparison to the combustion of this fuel in the sand bed, when the same maximum degree of reduction of NOx will be obtained for both types of beds.展开更多
In this paper we access the effects of two atmospheric variables (temperatureand relative humidity) on two important pollutants in the atmosphere(Nitrogen oxides (NOx) and carbon monoxide (CO)) by using one year(2016)...In this paper we access the effects of two atmospheric variables (temperatureand relative humidity) on two important pollutants in the atmosphere(Nitrogen oxides (NOx) and carbon monoxide (CO)) by using one year(2016) data of Addis Ababa. Temperature has impact on atmosphericmixing and cause for the reduction of NOx as temperature increases.There are positive correlation between temperature and CO concentrationfrom January to April with (R^2 = 0.69), negative correlation from Mayto August with (R2 = 0.92) and no correlation for the remaining months.NOx and CO have moderate positive and negative correlation with relativehumidity during the months January-April (R^2 = 0.294 for NOx and R^2 =0291 for CO) and in the months May-August are R2 = 0.97 and R2 = 0.15for NOx and CO respectively. But there are no clear correlation betweenthe NOx and CO with relative humidity from September-December.NOx concentrations during wet season was almost about twice that of thedry season, but no such difference was observed in the case of CO. Theseasonal average air temperature in wet season is relatively lower than dryseason. NOx exhibited positive and CO negative seasonal correlations withrelative humidity.展开更多
Thermally assisted photodriven nitrogen oxidation to nitric oxide(NO)using air as a reactant is a promising way to supersede the traditional NO synthesis industry accompanied by huge energy expenditure and greenhouse ...Thermally assisted photodriven nitrogen oxidation to nitric oxide(NO)using air as a reactant is a promising way to supersede the traditional NO synthesis industry accompanied by huge energy expenditure and greenhouse gas emission.Meanwhile,breaking the N≡N triple bond(941 kJ·mol^(−1))in nitrogen is still challenging,and the development of more efficient catalysts is necessary.Herein,Ru single atoms decorated TiO_(2) nanosheets(Ru SAs/TiO_(2))were constructed and achieved superior performance for NO photosynthesis with a product rate of 192μmol g^(−1) h^(−1) and a quantum efficiency of 0.77% at 365 nm.Both ^(15)N isotope labeling experiments and in situ near ambient pressure X-ray photoelectron spectroscopy(in situ NAP-XPS)proved the origin of NO from N_(2) photooxidation.A series of in situ characterizations and theoretical calculations unveiled the reaction pathway of nitrogen photooxidation.Breaking the O-O bond to form(N-O)2-Ru intermediates was demonstrated as the rate-determining step.Importantly,a single-atomic structure was proven to inhibit the aggregation and inactivation of Ru,leading to outstanding durability.展开更多
Studies were carried out to investigate the outdoor air pollution levels in vehicular traffic junctions in the major cities of Nsukka, Enugu and semi-urban area of Awgu all in Enugu State, Nigeria using standard analy...Studies were carried out to investigate the outdoor air pollution levels in vehicular traffic junctions in the major cities of Nsukka, Enugu and semi-urban area of Awgu all in Enugu State, Nigeria using standard analytical procedures. PM</span><sub><span style="font-family:Verdana;">2.5</span></sub><span style="font-family:Verdana;"> was collected using Envirotech air sampler, APM 550 and analyzed gravimetrically. Other determined air pollutant gases such as SO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">, NO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">, O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> and CO were analyzed using colorimetric techniques. The mean hourly traffic density in the vehicular traffic junctions in Nsukka metropolis, Enugu metropolis and Awgu w</span></span><span style="font-family:Verdana;">ere</span><span style="font-family:""><span style="font-family:Verdana;"> 2015, 2873 and 587 respectively. The mean range of values of PM</span><sub><span style="font-family:Verdana;">2.5</span></sub><span style="font-family:Verdana;">, NO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">, SO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">, O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> and CO in vehicular traffic junctions within the investigated environments w</span></span><span style="font-family:Verdana;">ere</span><span style="font-family:""><span style="font-family:Verdana;"> 1.67 - 12.16 μg/m</span><sup><span style="font-family:Verdana;">3</span></sup><span style="font-family:Verdana;">, 3.72 - 23.83 μg/m</span><sup><span style="font-family:Verdana;">3</span></sup><span style="font-family:Verdana;">, 2.96 - 30.09 μg/m</span><sup><span style="font-family:Verdana;">3</span></sup><span style="font-family:Verdana;">, 5.45 - 66.54 μg/m</span><sup><span style="font-family:Verdana;">3</span></sup><span style="font-family:Verdana;"> and 1.18 - 15.17 ppm respectively. The mean levels of the determined air pollutants in the air around vehicular traffic junctions in Nsukka metropolis, Enugu metropolis and Awgu semi-urban area differed significantly. The mean levels of PM</span><sub><span style="font-family:Verdana;">2.5</span></sub><span style="font-family:Verdana;">, and CO in the air around vehicular traffic junctions in Enugu metropolis and CO in the air around traffic junctions in Nsukka metropolis were above the recommended permissible limits. Traffic density was therefore seen as the single most important factor contributing to the varying air pollution levels observed in the investigated environments.展开更多
基金Education Innovation Project of Shanghai,China(No.12ZZ069)Natural Science Foundation of Shanghai,China(No.11ZR1400400)+1 种基金Doctoral Fund of Ministry of Education of China(No.20130075110006)Modification Fiber Materials Project of the National Key Laboratory of China(No.LK1203)
文摘The catalytic oxidation of nitrogen oxide( NO) from waste gas was investigated using advanced oxidation process based on sulfate radicals. The manganese oxide immobilized on graphene oxide( GO) can activate peroxymonosulfate( PMS) for the oxidation of NO in waste gas. The Mn3O4 / GO catalyst system was characterized via X-ray diffraction( XRD), Fourier transform infrared spectrocopy( FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy( XPS), energy dispersive X-ray spectroscopy( EDS),and scanning electron microscope( SEM).The results showed that Mn3O4 was distributed on GO. The Mn3O4 /GO catalyst system exhibited efficient activity for NO oxidation when the Mn3O4 /GO catalyst had an optimum Mn3O4 loading. In addition,the best catalytic oxidation could be achieved within 60 min with 0. 25 mmol /L Mn3 O4 /GO catalyst, and2 mmol /L PMS dosage at 25 ℃. The catalysts also exhibited stable performance after several rounds of regeneration. Therefore,the results may have significant technical implication for utilizing Mn3O4 /PMS to oxidize NO for offgas treatment.
基金supported by the Beijing Post-Doctoral Work Foundation under Grant (No. 2011ZZ-86)the Beijing Science and Technology Nova Project (No.2010B029)the National Natural Science Foundation of China (No. 40905060)
文摘Based on observational data of ozone(O3) and nitrogen oxide(NOx) mixing ratios on the ground and at high altitude in urban areas of Beijing during a period of six days in November 2011,the temporal and spatial characteristics of mixing ratios were analyzed.The major findings include:urban O3 mixing ratios are low and NOx mixing ratios are always high near the road in November.Vertical variations of the gases are significantly different in and above the planetary boundary layer.The mixing ratio of O3 is negatively correlated with that of NOx and they are positively correlated with air temperature,which is the main factor directly causing vertical variation of O3 and NOx mixing ratios at 600-2100m altitude.The NOx mixing ratios elevated during the heating period,while the O3 mixing ratios decreased:these phenomena are more significant at high altitudes compared to lower altitudes.During November,air masses in the urban areas of Beijing are brought by northwesterly winds,which transport O3 and NOx at low mixing ratios.Due to Beijing's natural geographical location,northwest air currents are beneficial to the dilution and dispersion of pollutants,which can result in lower O3 and NOx background values in the Beijing urban area.
文摘The resonance-enhanced multiphoton ionization (REMPI) spectrum of NO has been obtained. The spectral lines can be attributed to NO D2∑←X2П transitions. NO molecules are ionized via the resonant intermediate D2∑ states and by (3+2) REMPI process.
基金supported by National Natural Science Foundation of China(21878210)Shanxi “1331”Civil Clean Fuel Engineering Research Center,Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(2019L0313)+1 种基金Patent Promotion and implementation in Shanxi Province(20200719)sponsored by Taiyuan Green Coke Energy Co.,Ltd.(China)。
文摘The emission of NOx during coal combustion contributes to the formation of acid rain and photochemical smog,which would seriously affect the quality of atmospheric environment.Therefore,the decrease of NOx is of great importance for improving the efficient utilization of coal.The present review comprehensively summarized the influence factors and mechanisms of migration and transformation of nitrogen during the coal pyrolysis and combustion based on experimental study and quantum chemical calculation.Firstly,in the process of pyrolysis:the occurrence state and transformation of nitrogen were concluded.The influence of temperature,atmosphere,heating rate and catalyst on formation of NOx precursor and nitrogen migration path at the molecular level were summarized;Secondly,during the process of combustion:the influence of temperature,ambient oxygen concentration,physical structure of coal char,catalyst on heterogeneous oxidation of char(N)were summarized;The effects of char surface properties,catalyst and ambient atmosphere on heterogeneous reduction of NOx were also concluded.Based on the quantum chemical calculation,the reaction path of heterogeneous oxidation of char-N and heterogeneous reduction of NOx were described in detail.Current studies focus more on the generation of HCN and NH3,but in order to reduce the pollution of NOx from the source,it is necessary to further improve the process conditions and the optimal formula of producing more N2 during pyrolysis,as well as clarify the path of the generation of N2.Experiments study and quantum chemistry calculation should be combined to complete the research of directional nitrogen reduction during pyrolysis and denitration during combustion.
文摘The gas-phase conversion of U3O8, MoO3, SrO, and their mechanical mixtures, and also of ZrO2 into water-soluble compounds in the atmosphere of (NOx + vapor H2O) or HNO3 (vapor) was studied. In the course of gas-phase conversion, U3O8 and SrO transform into water-soluble compounds (nitrates, hydroxonitrates), whereas MoO3 and ZrO2 undergo no changes. The principal possibility of separating U from Mo and Zr by gas-phase conversion of the oxides in the atmosphere of (NOx + vapor H2O) or HNO3 (vapor) was demonstrated.
基金supported by the National Natural Science Foundation of China (Grant Nos. 91537209 and 91644224)
文摘Lightning-generated nitrogen oxides(LNO_(x))have a major influence on the atmosphere and global climate change.Therefore,it is of great importance to obtain a more accurate estimation of LNO_(x).The aim of this study is to provide a reference for the accurate estimation of the total LNO_(x) in the mainland of China based on cloud-to-ground lightning(CG)location data from 2014 to 2018.The energy of each CG flash was based on the number of return strokes per CG flash,the peak current of each return stroke,and the assumed CG breakdown voltage.The energy of intracloud lightning(IC)was based on the estimated frequencies of IC and the assumed energy of each IC flash.Combining the energy of lightning and the number of nitric oxide(NO)molecules produced by unit energy(ρno),the total LNO_(x) production in the mainland of China was determined.The LNO_(x) in the mainland of China estimated in this study is in the range(0.157-0.321)×10^(9) kg per year[Tg(N)yr-1],which is on the high end of other scholars’works.Negative cloud-to-ground lightning(NCG)flashes produce the most moles of NO_(x),while positive cloud-to-ground lightning(PCG)flashes produce the least total moles of NO_(x).The breakdown voltage of PCG is greater than that of IC or NCG,while the latter has a greater output of LNO_(x).
基金financial supports from the “Transformational Technologies for Clean Energy and Demonstration”, Strategic Priority Research Program of Chinese Academy of Sciences (XDA21040400)。
文摘Burning coal briquettes or biomass pellets in household decoupling stoves is of significance to the reduction of residential pollutant emissions such as NO and CO. In order to make full use of the superiority of decoupling combustion technology, the household stoves should be specially designed and optimized to adapt to fuel types and combustion characteristics. Using numerical simulation and experimental validation, this study quantitatively clarified that the reducibility of devolatilization char plays an important role in the suppression of NO emission in the decoupling combustion of coal, while the reducibility of pyrolysis gases has a dominant effect on the reduction of NO in the decoupling combustion of biomass. An optimal parameter combination of throat height and grate angle was obtained for the simultaneous suppression of NO and CO emissions in the household decoupling stove burning coal briquettes. Two types of decoupling stoves were developed to enable the clean combustion of biomass pellets. The A-type biomass stove with a multi-pass smoke tunnel shows a better comprehensive NO and CO reduction effectiveness than the B-type biomass stove consisting of a two-stage grate structure and an S-shaped pyrolysis chamber. The optimal structural parameters provided references for the design and manufacture of commercial decoupling coal and biomass stoves.
基金supported by the National Natural Science Foundation of China(No.51472220 and No.51872265)Collaborative Innovation Major Special Project of Zhengzhou(No.20XTZX12025)。
文摘To meet the emission standard of nitrogen oxides(NOx)in the flue gas of batch furnaces through dry adsorption,a calcium-silica inorganic adsorbent was prepared with limestone and quartz as raw materials.Sample Cu-BTC 1#was obtained by solvothermal synthesis,drying and purification in vacuum at 120℃using trimesic acid(H3BTC)and copper nitrate trihydrate(Cu(NO_(3))2·3H_(2)O)as raw materials;likewise,sample Cu-BTC 3#was obtained at 200℃.Sample Cu-BTC 2#was obtained by hydrothermal synthesis,drying and purification in air(metal-organic frameworks,1,3,5-benzene tricarboxylic acid copper).The two types of materials were tested in terms of the NO_(2) adsorption,and then the specific surface area,pore volume,NO_(2) adsorption performance,phase composition,microstructure and thermal stability of the adsorbent materials were exploredvia N_(2) physical adsorption-desorption,SEM,XRD and TG characterization.The results show that:(1)the Cu-BTC samples have higher adsorption capacity than the calcium-silica adsorbent,in which sample Cu-BTC 3#has the largest specific surface area and pore volume,thus adsorption capacity for NO_(2);(2)the calcium-silica adsorbent has better thermal stability and lower total mass loss during the entire process than the Cu-BTC samples;sample Cu-BTC 2#has the best thermal stability among the three Cu-BTC samples,and the metal Cu active sites of the Cu-BTC samples can be exposed at least above 150℃.
文摘Ammonia (NH<sub>3</sub>) dissociation and oxidation in a cylindrical quartz reactor has been experimentally studied for various inlet NH<sub>3</sub> concentrations (5%, 10%, and 15%) and reactor temperatures between 700 K and 1000 K. The thermal effects during both NH<sub>3</sub> dissociation (endothermic) and oxidation (exothermic) were observed using a bundle of thermocouples positioned along the central axis of the quartz reactor, while the corresponding NH<sub>3</sub> conversions and nitrogen oxides emissions were determined by analysing the gas composition of the reactor exit stream. A stronger endothermic effect, as indicated by a greater temperature drop during NH<sub>3</sub> dissociation, was observed as the NH<sub>3</sub> feed concentration and reactor temperature increased. During NH<sub>3</sub> oxidation, a predominantly greater exothermic effect with increasing NH<sub>3</sub> feed concentration and reactor temperature was also evident;however, it was apparent that NH<sub>3</sub> dissociation occurred near the reactor inlet, preceding the downstream NH<sub>3</sub> and H<sub>2</sub> oxidation. For both NH<sub>3</sub> dissociation and oxidation, NH<sub>3</sub> conversion increased with increasing temperature and decreasing initial NH<sub>3</sub> concentration. Significant levels of NO<sub>X</sub> emissions were observed during NH<sub>3</sub> oxidation, which increased with increasing temperature. From the experimental results, it is speculated that the stainless-steel in the thermocouple bundle may have catalysed NH<sub>3</sub> dissociation and thus changed the reaction chemistry during NH<sub>3</sub> oxidation.
基金supported by the National Key R&D Program of China (2021YFB4000402)the National Natural Science Foundation of China (22022503)。
文摘The direct oxidation of nitrogen is a potential pathway to achieving the zero-carbon-emission synthesis of nitric acid or nitrate, because it does not involve ammonia synthesis and additional ammonia oxidation processes. However, the slow kinetics of nitrogen oxidation and the difficult selective control of oxidation products hinder the development of this process. In this study, a plasma-driven gas-liquid relay reaction system was developed to overcome these limitations. A typical feature of this reaction system is that it can efficiently generate NO_x under plasma exposure;moreover, the specific anions in the absorption solution can be oxidized to strong oxidants capable of relay oxidation of low-valence nitrogen oxides. This feature allows for the deep oxidation of nitrogen, thus enabling the oxidation products of nitrogen to exist in high-valence states in the absorption solution. For experimental verification, we achieved the 100% selective synthesis of nitrate under plasma exposure, with air as the supply gas and a sodium sulfate solution as the absorption solution.
文摘The effects of NOx(in a ratio of NO∶NO2=9∶1) and SO2in cathode streamonthe performance of a single proton ex-change membrane fuel cell(PEMFC) were investigated.NOxwith concentrations of 1×10-3%(in volume,the same as fol-lows),1.4×10-2%and 1×10-3%could cause significant detri mental effects on the cell performance.However,nearly com-plete recovery of the cell performance could be observed after NOxwas shut off and purged with clean air.The electrochemicalmeasurements suggested that thei mpacts of NOxresulted mainlyfromthe superposition of the oxygen reduction reaction(ORR),NOand HNO2oxidation reactions,and the increased cathodic i mpedance.Trace SO2with concentrations of 5×10-6%,5×10-3%,2×10-4%and 3.2×10-4%influenced the cell muchseverer,which could be attributed toits strong adsorption onthesurface of Pt atoms.The cell performance could not be completely recovered after purged with clean air and cyclic voltammetry(CV) tests,due to the changes of electrochemical i mpedance spectroscopy(EIS) and electrochemical active surface(EAS) causedby surface state change after SO2exposure.
文摘Emissions of exhaust gases and particulate matter from a dual fuel marine engine using methanol as fuel with marine gasoil as pilot fuel have been examined for a ferry during operation.The emission factor for nitrogen oxides is lower than what is typically found for marine gasoil but does not reach the tier III limit.The emissions of particulate matter are significantly lower than for fuel oils and similar to what is found for LNG engines.The main part of the particles can be found in the ultrafine range with the peak being at around 18 nm.About 93%of the particles are evaporated and absorbed when using a thermodenuder,and thus a large majority of the particles are volatile.Methanol is a potential future marine fuel that will reduce emissions of air pollutants and can be made as a biofuel to meet emission targets for greenhouse gases.
基金Open access funding provided by Universita degli Studi di Napoli Federico II within the CRUI-CARE Agreement.
文摘In this study,a model is developed to simulate the dynamics of an internal combustion engine,and it is calibrated and validated against reliable experimental data,making it a tool that can effectively be adopted to conduct emission predictions.In this work,the Ricardo WAVE software is applied to the simulation of a particular marine diesel engine,a four-stroke engine used in the maritime field.Results from the bench tests are used for the calibration of the model.Finally,the calibration of the model and its validation with full-scale data measured at sea are presented.The prediction includes not only the classic engine operating parameters for a comparison with surveys but also an estimate of nitrogen oxide emissions,which are compared with similar results obtained with emission factors.The calibration of the model made it possible to obtain an overlap between the simulation results and real data with an average error of approximately 7%on power,torque,and consumption.The model provides encouraging results,suggesting further applications,such as in the study on transient conditions,coupling of the engine model with the ship model for a complete simulation of the operating conditions,and optimization studies on consumption and emissions.The availability of the emission data during the sea trial and validated simulation results are the strengths and novelties of this work.
文摘This work examines the effect of butanol as an oxygenated additive to lower carbon monoxide,smoke,nitrogen oxide and hydrocarbon emissions and to improve the performance aspects of Calophyllum inophyllum(Punnai)biodiesel.Singlecylinder,oil-cooled compression ignition engines are employed in this work.Neat Punnai biodiesel(P100)is blended with butanol at 10%and 20%by volume and labelled as B10 P90 and B20 P80,respectively.Methanol and alkaline catalyst(KOH)were used for the transesterification process for biodiesel production.The transesterification technique yielded 88%biodiesel from raw Punnai oil.Engine tests resulted in lower CO,smoke,NO_x and HC emissions when fuelled with both butanol blends when compared to P100.In addition,BSFC(brake-specific fuel consumption)reduced and BTE(brake thermal effciency)increased with the inclusion of butanol blends(B10 and B20)to neat Punnai biodiesel.
文摘BACKGROUND Type 1 diabetes originates from gene-environment interactions,with increasing incidence over time.AIM To identify correlates of childhood type 1 diabetes in European countries using an ecological approach.Several environmental variables potentially influencing the onset of type 1 diabetes have been previously evaluated.However,the relationships between epidemiologic data and exposure to toxic airborne molecules are scarcely studied.METHODS We employed an ecological model to explore,in a wide time period(1990-2018),associations between type 1 diabetes incidence in 19 European countries(systematic literature review)and the nationwide production of five widely diffused air pollutants:particulate matter<10μm(PM10),nitrogen oxides(NO),non-methane volatile organic compounds(VOCs),sulphur oxide(SO2),and ammonia.RESULTS Data confirm a raising incidence of type 1 diabetes in 18 out of 19 explored countries.The average difference(last vs first report,all countries)was+6.9×100000/year,with values ranging from-1.4(Germany)to+16.6(Sweden)per 100000/year.Although the overall production of pollutants decreased progressively from 1990 to 2018,type 1 diabetes incidence was positively associated with the nationwide emissions of PM10,VOCs,and NO but not with those of SO2 and ammonia.Type 1 diabetes incidence was significantly higher in countries with high emissions than in those with low emissions of PM10(27.5±2.4 vs 14.6±2.4×100000 residents,respectively),VOCs(24.5±4.4 vs 13.2±1.7×100000 residents,respectively),and NO(26.6±3 vs 13.4±2.4×100000 residents,respectively),but not of SO2 or ammonia.CONCLUSION Evidence justify further studies to explore better links between long-term air quality and type 1 diabetes onset at the individual level,which should include exposures during pregnancy.In this respect,type 1 diabetes could be,at least in part,a preventable condition.Thus,primary prevention policies acting through a marked abatement of pollutant emissions might attenuate future type 1 diabetes incidence throughout Europe.
基金supported by National Natural Science Foundation of China under Grant Nos.11405022,11475039, 11675095'Dalian High Level Talent Innovation Support Project' under Grant Nos.2015R050 and 2016RQ020
文摘In this paper,removal of nitrogen oxide(NO) is investigated in capacitive atmospheric pressure discharges driven by both radio-frequency(RF) and trapezoidal pulsed power with a onedimensional self-consistent fluid model.The results show that the number density of NO could be reduced significantly once a short pulse of low duty ratio is additionally applied to the RF power.It is found that the process of NO removal by the pulse-modulated RF discharge could be divided into three stages:the quick reaction stage,the NO removal stage,and the sustaining stage.Furthermore,the temporal evolution of particle densities is analyzed,and the key reactions in each stage are discovered.Finally,the influence on the removal efficiency of the voltage amplitude of the pulse and the RF voltage amplitude is investigated.
文摘In the present study reduction of nitrogen oxides using reburning technology, during combustion of sewage sludge (fuel I) and the mixture of sewage sludge, wasted bleaching earth and CaO (fuel II), was carried out. The experimental works were conducted in a laboratory-scale fluidized bed reactor (power up to 10 kW) with application of two types of beds: chemically inert bed (sand) and chemically active bed (CaO). The second combustion (reburning) zone in the reactor was formed by dosing into an area above the bed, additional gaseous fuel (propane). Obtained reduction in emissions of nitrogen oxides in both types of beds was at a level 70% - 79%. Additionally bed of CaO has the desulfurizing effect and also reduces the CO concentration in the exhaust fumes. A significant drawback of active bed is the adverse effect on increase of the primary NO which enters the second combustion zone. The result of this fact is higher NOx emission during combustion of the same fuel in bed of CaO in comparison to the combustion of this fuel in the sand bed, when the same maximum degree of reduction of NOx will be obtained for both types of beds.
文摘In this paper we access the effects of two atmospheric variables (temperatureand relative humidity) on two important pollutants in the atmosphere(Nitrogen oxides (NOx) and carbon monoxide (CO)) by using one year(2016) data of Addis Ababa. Temperature has impact on atmosphericmixing and cause for the reduction of NOx as temperature increases.There are positive correlation between temperature and CO concentrationfrom January to April with (R^2 = 0.69), negative correlation from Mayto August with (R2 = 0.92) and no correlation for the remaining months.NOx and CO have moderate positive and negative correlation with relativehumidity during the months January-April (R^2 = 0.294 for NOx and R^2 =0291 for CO) and in the months May-August are R2 = 0.97 and R2 = 0.15for NOx and CO respectively. But there are no clear correlation betweenthe NOx and CO with relative humidity from September-December.NOx concentrations during wet season was almost about twice that of thedry season, but no such difference was observed in the case of CO. Theseasonal average air temperature in wet season is relatively lower than dryseason. NOx exhibited positive and CO negative seasonal correlations withrelative humidity.
基金financially supported by the National Natural Science Foundation of China(nos.22071173 and 21871206)the Natural Science Foundation of Tianjin City(no.17JCQNJC03200).
文摘Thermally assisted photodriven nitrogen oxidation to nitric oxide(NO)using air as a reactant is a promising way to supersede the traditional NO synthesis industry accompanied by huge energy expenditure and greenhouse gas emission.Meanwhile,breaking the N≡N triple bond(941 kJ·mol^(−1))in nitrogen is still challenging,and the development of more efficient catalysts is necessary.Herein,Ru single atoms decorated TiO_(2) nanosheets(Ru SAs/TiO_(2))were constructed and achieved superior performance for NO photosynthesis with a product rate of 192μmol g^(−1) h^(−1) and a quantum efficiency of 0.77% at 365 nm.Both ^(15)N isotope labeling experiments and in situ near ambient pressure X-ray photoelectron spectroscopy(in situ NAP-XPS)proved the origin of NO from N_(2) photooxidation.A series of in situ characterizations and theoretical calculations unveiled the reaction pathway of nitrogen photooxidation.Breaking the O-O bond to form(N-O)2-Ru intermediates was demonstrated as the rate-determining step.Importantly,a single-atomic structure was proven to inhibit the aggregation and inactivation of Ru,leading to outstanding durability.
文摘Studies were carried out to investigate the outdoor air pollution levels in vehicular traffic junctions in the major cities of Nsukka, Enugu and semi-urban area of Awgu all in Enugu State, Nigeria using standard analytical procedures. PM</span><sub><span style="font-family:Verdana;">2.5</span></sub><span style="font-family:Verdana;"> was collected using Envirotech air sampler, APM 550 and analyzed gravimetrically. Other determined air pollutant gases such as SO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">, NO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">, O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> and CO were analyzed using colorimetric techniques. The mean hourly traffic density in the vehicular traffic junctions in Nsukka metropolis, Enugu metropolis and Awgu w</span></span><span style="font-family:Verdana;">ere</span><span style="font-family:""><span style="font-family:Verdana;"> 2015, 2873 and 587 respectively. The mean range of values of PM</span><sub><span style="font-family:Verdana;">2.5</span></sub><span style="font-family:Verdana;">, NO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">, SO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">, O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> and CO in vehicular traffic junctions within the investigated environments w</span></span><span style="font-family:Verdana;">ere</span><span style="font-family:""><span style="font-family:Verdana;"> 1.67 - 12.16 μg/m</span><sup><span style="font-family:Verdana;">3</span></sup><span style="font-family:Verdana;">, 3.72 - 23.83 μg/m</span><sup><span style="font-family:Verdana;">3</span></sup><span style="font-family:Verdana;">, 2.96 - 30.09 μg/m</span><sup><span style="font-family:Verdana;">3</span></sup><span style="font-family:Verdana;">, 5.45 - 66.54 μg/m</span><sup><span style="font-family:Verdana;">3</span></sup><span style="font-family:Verdana;"> and 1.18 - 15.17 ppm respectively. The mean levels of the determined air pollutants in the air around vehicular traffic junctions in Nsukka metropolis, Enugu metropolis and Awgu semi-urban area differed significantly. The mean levels of PM</span><sub><span style="font-family:Verdana;">2.5</span></sub><span style="font-family:Verdana;">, and CO in the air around vehicular traffic junctions in Enugu metropolis and CO in the air around traffic junctions in Nsukka metropolis were above the recommended permissible limits. Traffic density was therefore seen as the single most important factor contributing to the varying air pollution levels observed in the investigated environments.
