NOx Sources Research Articles

Source apportionment and health effect of NOx over the Pearl River Delta region in southern China

As one of the most notorious atmospheric pollutants, NOx not only promotes the formation of ozone but also has adverse health effects on humans. It is therefore of great importance to study the sources of NOx and its effects on human health. The Comprehensive Air Quality Model (CAMx) modeling system and ozone source apportionment technology (OSAT) were used to study the contribution of NOx from different emission sources over southern China. The results indicate that heavy duty diesel vehicles (HDDVs) and industrial point sources are the two major local NOx sources, accounting for 30.8% and 18.5% of local NOx sources, respectively. In Hong Kong, marine emissions contributed around 43.4% of local NOx in 2011. Regional transport is another important source of this pollutant, especially in February and November, and it can contribute over 30% of ambient NOx on average. Power plant point emission is an significant regional source in Zhuhai, Zhongshan and Foshan. The total emission sources are estimated to cause 2119 (0–4405) respiratory deaths and 991 (0–2281) lung cancer deaths due to long-term exposure to NOx in the Pearl River Delta region. Our results suggest that local governments should combine their efforts and vigorously promote further reduction of NOx emissions, especially for those sources that make a substantial contribution to NOx emissions and affect human health: HDDV, LDGV, industrial point sources and marine sources.

On the Possibilities of Using Alternative Fuels in ICE Powered Lawn Mowers and Tractors to Meet Phase III Emissions Standards

There is a need to use alternative fuels in Internal Combustion Engines (ICE) powered lawn care equipment used around residential, office and reserved areas. This will enable this equipment to meet Phase III emissions standards set by the Environmental Protection Agency. One method of reducing emissions from trimmers, lawn mowers, tractors and blowers is to use alcohol fuels in the next generation of ICE powered devices and also, to make it adaptable to operate on flex-fuels. These devices are not only a great source of noise pollution, they are also a major source of hydrocarbon, NOx and CO emissions in the residential neighbourhood from spring to the fall seasons, hence, the need to mandate the use of alcohol and flex fuels to lowers emissions. These changes will require a slight modification of the engine, by way of increasing the compression ratio on one hand, and modifying the fuel system: tank, fuel lines, and fuel dispensing system (carburetor) to meet flex-fuel requirements. This proposed engine modification will meet Phase 3 emissions standards as alcohol fuels possess superior combustion characteristics and lower emissions.

Biofuels, vehicle emissions, and urban air quality.

Increased biofuel content in automotive fuels impacts vehicle tailpipe emissions via two mechanisms: fuel chemistry and engine calibration. Fuel chemistry effects are generally well recognized, while engine calibration effects are not. It is important that investigations of the impact of biofuels on vehicle emissions consider the impact of engine calibration effects and are conducted using vehicles designed to operate using such fuels. We report the results of emission measurements from a Ford F-350 fueled with either fossil diesel or a biodiesel surrogate (butyl nonanoate) and demonstrate the critical influence of engine calibration on NOx emissions. Using the production calibration the emissions of NOx were higher with the biodiesel fuel. Using an adjusted calibration (maintaining equivalent exhaust oxygen concentration to that of the fossil diesel at the same conditions by adjusting injected fuel quantities) the emissions of NOx were unchanged, or lower, with biodiesel fuel. For ethanol, a review of the literature data addressing the impact of ethanol blend levels (E0-E85) on emissions from gasoline light-duty vehicles in the U.S. is presented. The available data suggest that emissions of NOx, non-methane hydrocarbons, particulate matter (PM), and mobile source air toxics (compounds known, or suspected, to cause serious health impacts) from modern gasoline and diesel vehicles are not adversely affected by increased biofuel content over the range for which the vehicles are designed to operate. Future increases in biofuel content when accomplished in concert with changes in engine design and calibration for new vehicles should not result in problematic increases in emissions impacting urban air quality and may in fact facilitate future required emissions reductions. A systems perspective (fuel and vehicle) is needed to fully understand, and optimize, the benefits of biofuels when blended into gasoline and diesel.

Nitrogen Isotope Exchange Between NO and NO2 and Its Implication for 15N Variations in Tropospheric NOx

Nitrogen oxides (NOx = NO + NO2) are trace gases that have numerous sources that include vehicles, power plants, lightning, soil emissions, agriculture, and biomass burning. It is important to estimate the budgets of these emission sources because NOx play an important role in air quality, climate, and human health. Analysis of the nitrogen stable isotope ratio (15N/14N) has been suggested as a useful method for partitioning NOx sources, as emission sources often have characteristic 15N/14N ratios (“fi ngerprints”). However, the effects of chemical and physical processes on 15N/14N ratios of NOx have not been researched in depth, which limits this isotopic technique. It has been suggested that the nitrogen isotope exchange between NO and NO2 has an infl uence on the partitioning of 15N between these two molecules. However, previous experimental and theoretical studies disagree about the value of this isotope exchange process. We have experimentally measured this isotope exchange process in which NO and NO2 were equilibrated in a vacuum system and NO2 was selectively removed from the system and measured for its 15N/14N ratio. Our experimental values agree exceptionally well with the theoretically predicted value, using corrections for anharmonicity. Using this data, we were able to model a diurnal cycle and seasonal changes in the distribution of 15N/14N ratios between NO and NO2 resulting from nitrogen isotopic exchange. Future research will measure 15N/14N ratios of NOx in ambient air to see if our predicted diurnal and seasonal change is correct.

Modeling the Current and Future Roles of Particulate Organic Nitrates in the Southeastern United States.

Organic nitrates are an important aerosol constituent in locations where biogenic hydrocarbon emissions mix with anthropogenic NOx sources. While regional and global chemical transport models may include a representation of organic aerosol from monoterpene reactions with nitrate radicals (the primary source of particle-phase organic nitrates in the Southeast United States), secondary organic aerosol (SOA) models can underestimate yields. Furthermore, SOA parametrizations do not explicitly take into account organic nitrate compounds produced in the gas phase. In this work, we developed a coupled gas and aerosol system to describe the formation and subsequent aerosol-phase partitioning of organic nitrates from isoprene and monoterpenes with a focus on the Southeast United States. The concentrations of organic aerosol and gas-phase organic nitrates were improved when particulate organic nitrates were assumed to undergo rapid (τ = 3 h) pseudohydrolysis resulting in nitric acid and nonvolatile secondary organic aerosol. In addition, up to 60% of less oxidized-oxygenated organic aerosol (LO-OOA) could be accounted for via organic nitrate mediated chemistry during the Southern Oxidants and Aerosol Study (SOAS). A 25% reduction in nitrogen oxide (NO + NO2) emissions was predicted to cause a 9% reduction in organic aerosol for June 2013 SOAS conditions at Centreville, Alabama.

Global modeling of the C1–C3 alkyl nitrates using STOCHEM-CRI

The atmospheric global budget and distribution of C1–C3 alkyl nitrates have been investigated using a global three-dimensional chemistry transport model, STOCHEM-CRI. Alkyl nitrates (RONO2) are significant NOx reservoir species and the more detailed VOC oxidation mechanism (CRI v2-R5) leads to greater photochemical production. RONO2 are significant sources of NOx in regions remote from NOx sources. The study shows that the global burden and the atmospheric life-time of C1–C3 alkyl nitrates are 113 Gg and 9–10 days, respectively, which are in excellent agreement with estimates established by previous studies. The abundance of alkyl nitrates have been found to be higher in the continental atmosphere, with CH3ONO2 mixing ratios up to 20 ppt over the Amazon rainforest. Up to 15, 10, 2, and 5 ppt of modelled CH3ONO2, C2H5ONO2, n-C3H7ONO2 and i-C3H7ONO2 have been found in the northern hemisphere over regions with large anthropogenic emissions of NOx and VOCs. The combination of atmospheric production and long-range transport led to high alkyl nitrate levels at high latitudes. The model performance for C1–C3 alkyl nitrates was established using observations from nine flights and nine field campaigns. The comparison shows a tendency towards model under-prediction of the observations, particularly in the southern hemispheric marine boundary layer, possibly due to the absence of oceanic production mechanisms and air-sea exchange processes in the model. The discrepancies between model and observed seasonal cycles, especially of CH3ONO2, in both hemispheres are discussed.

Spatial distribution of pollutant emissions from crop residue burning in the Punjab and Sindh provinces of Pakistan: uncertainties and challenges.

Emissions of gaseous and particulate pollutants from burning of wheat straw, rice straw, cotton straw, and bagasse were studied for the two agricultural-activity-dominated provinces of Pakistan: the Punjab and Sindh. Emission estimates, inventory, and allocation maps indicated distinct patterns of pollutant emissions in the two provinces. Comparative pollutant emission analysis revealed that the Punjab province produced higher pollutants from agricultural biomass burning than Sindh province. Total emissions from these two provinces were estimated to be 16,084.04 Gg (16.08 Tg) for the year 2006/2007. Wheat straw was found to be the dominant source of CO, CO2, SO2, NOx, and EC emissions in the both provinces. However, for the emissions of CH4, NH3, EC, and OC, the Punjab and Sindh provinces differed markedly for the crop residue share in these pollutant emissions. Rice straw was found to be the largest contributor of CH4 (51%) and NH3 (65%) in Sindh province. When total emissions from biomass burning were considered at provincial level, wheat straw and bagasse were the major crop residues which accounted for 72 and 14% of pollutant emissions, respectively, in the Punjab province, whereas, in Sindh province, the order of crop residue contribution in total emission was as follows: wheat (59%) > bagasse (19%) > rice (14%) > cotton (7%). Emission inventory data of total pollutants per unit area under cultivation (Mg ha(-1)) revealed that Sindh province produced higher emissions per hectare for wheat straw, rice straw, and bagasse than the Punjab province.

OMI tropospheric NO<sub>2</sub> air mass factors over South America: effects of biomass burning aerosols

Abstract. Biomass burning is an important and uncertain source of aerosols and NOx (NO + NO2) to the atmosphere. Satellite observations of tropospheric NO2 are essential for characterizing this emissions source, but inaccuracies in the retrieval of NO2 tropospheric columns due to the radiative effects of aerosols, especially light-absorbing carbonaceous aerosols, are not well understood. It has been shown that the O2–O2 effective cloud fraction and pressure retrieval is sensitive to aerosol optical and physical properties, including aerosol optical depth (AOD). Aerosols implicitly influence the tropospheric air mass factor (AMF) calculations used in the NO2 retrieval through the effective cloud parameters used in the independent pixel approximation. In this work, we explicitly account for the effects of biomass burning aerosols in the Ozone Monitoring Instrument (OMI) tropospheric NO2 AMF calculation for cloud-free scenes. We do so by including collocated aerosol extinction vertical profile observations from the CALIOP instrument, and aerosol optical depth (AOD) and single scattering albedo (SSA) retrieved by the OMI near-UV aerosol algorithm (OMAERUV) in the DISAMAR radiative transfer model. Tropospheric AMFs calculated with DISAMAR were benchmarked against AMFs reported in the Dutch OMI NO2 (DOMINO) retrieval; the mean and standard deviation of the difference was 0.6 ± 8 %. Averaged over three successive South American biomass burning seasons (2006–2008), the spatial correlation in the 500 nm AOD retrieved by OMI and the 532 nm AOD retrieved by CALIOP was 0.6, and 68 % of the daily OMAERUV AOD observations were within 30 % of the CALIOP observations. Overall, tropospheric AMFs calculated with observed aerosol parameters were on average 10 % higher than AMFs calculated with effective cloud parameters. For effective cloud radiance fractions less than 30 %, or effective cloud pressures greater than 800 hPa, the difference between tropospheric AMFs based on implicit and explicit aerosol parameters is on average 6 and 3 %, respectively, which was the case for the majority of the pixels considered in our study; 70 % had cloud radiance fraction below 30 %, and 50 % had effective cloud pressure greater than 800 hPa. Pixels with effective cloud radiance fraction greater than 30 % or effective cloud pressure less than 800 hPa corresponded with stronger shielding in the implicit aerosol correction approach because the assumption of an opaque effective cloud underestimates the altitude-resolved AMF; tropospheric AMFs were on average 30–50 % larger when aerosol parameters were included, and for individual pixels tropospheric AMFs can differ by more than a factor of 2. The observation-based approach to correcting tropospheric AMF calculations for aerosol effects presented in this paper depicts a promising strategy for a globally consistent aerosol correction scheme for clear-sky pixels.

Nitrogen Isotope Composition of Thermally Produced NOx from Various Fossil-Fuel Combustion Sources.

The nitrogen stable isotope composition of NOx (δ(15)N-NOx) may be a useful indicator for NOx source partitioning, which would help constrain NOx source contributions in nitrogen deposition studies. However, there is large uncertainty in the δ(15)N-NOx values for anthropogenic sources other than on-road vehicles and coal-fired energy generating units. To this end, this study presents a broad analysis of δ(15)N-NOx from several fossil-fuel combustion sources that includes: airplanes, gasoline-powered vehicles not equipped with a three-way catalytic converter, lawn equipment, utility vehicles, urban buses, semitrucks, residential gas furnaces, and natural-gas-fired power plants. A relatively large range of δ(15)N-NOx values was measured from -28.1‰ to 8.5‰ for individual exhaust/flue samples that generally tended to be negative due to the kinetic isotope effect associated with thermal NOx production. A negative correlation between NOx concentrations and δ(15)N-NOx for fossil-fuel combustion sources equipped with selective catalytic reducers was observed, suggesting that the catalytic reduction of NOx increases δ(15)N-NOx values relative to the NOx produced through fossil-fuel combustion processes. Combining the δ(15)N-NOx measured in this study with previous published values, a δ(15)N-NOx regional and seasonal isoscape was constructed for the contiguous U.S., which demonstrates seasonal and regional importance of various NOx sources.

NOX EMISSION MODELLING FROM INDUSTRIAL STEAM BOILERS

Previous researches often emphasize on the sources and effects of air pollutants in the environment and human population. A part of those studies were done in order to explore the spread or distribution pattern of those pollutants, especially regarding the emission from industrial steam boilers. It is very important to evaluate the transfer trend of air pollutants at both local and global scales. In this study, Industrial Source Complex Short Term Version 3 (ISCST3) model has been used to predict the distribution of NOx emitted from industrial steam boilers in the District of Hulu Langat, Selangor. The result of analyses indicates that the emission rates for steam boilers were ranging from 0.0083 kg NOx/hour to as high as 0.2771 kg NOx/hour while the total emission load was 1.9969 kg NOx­/hour. The evaluation on dispersion contour shows that the concentration of NOx was higher in 1-hour reading than 24-hour value. The highest concentration of NOx was predicted to be within 104.65 km2 from the sources of NOx (steam boilers).

Projected Changes in NOx Emissions from Lightning as a Result of 2000–2050 Climate Change

Lightning is one of the most important natural sources of atmospheric NOx. The authors investigate the 2000-2050 changes in NOx emissions from lightning using the global three-dimensional Goddard E...

Characteristics of Gaseous Pollutants at a Regional Background Station in Southern China

Measurements of gaseous pollutants(O3, NOx, SO2, and CO) were conducted at Dinghushan background station in southern China from January to December 2013.The levels and variations of O3, NOx, SO2, and CO were analyzed and their possible causes discussed. The annual average concentrations of O3, NOx, SO2, and CO were 24.6 ± 23.9, 12.8 ± 10.2, 4.0 ± 4.8, and 348 ± 185 ppbv, respectively. The observed levels of the gaseous pollutants are comparable to those at other background sites in China. The most obvious diurnal variation of O3 was observed in autumn, with minima in the early morning and maxima in the afternoon. The diurnal variations of SO2 showed high values during the day. The diurnal cycles of NOx showed higher values in the morning and lower values during the night. Higher CO concentrations were observed in spring followed by winter, autumn, and summer. Biomass burning, in combination with the transport of regional pollution, is an important source of CO, SO2, and NOx in spring and winter. Backward trajectories were calculated and analyzed together with corresponding pollutant concentrations. The results indicate that air masses passing over polluted areas are responsible for the high concentrations of gaseous pollutants at the Dinghushan background station.

Theoretical calculation of nitrogen isotope equilibrium exchange fractionation factors for various NOy molecules

The nitrogen stable isotope ratio (15N/14N) of nitrogen oxides (NOx=NO+NO2) and its oxidation products (NOy=NOx+PAN (peroxyacetyl nitrate=C2H3NO5)+HNO3+NO3+HONO+N2O5+⋯+particulate nitrates) has been suggested as a tool for partitioning NOx sources; however, the impact of nitrogen (N) equilibrium isotopic fractionation on 15N/14N ratios during the conversion of NOx to NOy must also be considered, but few fractionation factors for these processes have been determined. To address this limitation, computational quantum chemistry calculations of harmonic frequencies, reduced partition function ratios (15β), and N equilibrium isotope exchange fractionation factors (αA/B) were performed for various gaseous and aqueous NOy molecules in the rigid rotor and harmonic oscillator approximations using the B3LYP and EDF2 density functional methods for the mono-substitution of 15N. The calculated harmonic frequencies, 15β, and αA/B are in good agreement with available experimental measurements, suggesting the potential to use computational methods to calculate αA/B values for N isotope exchange processes that are difficult to measure experimentally. Additionally, the effects of solvation (water) on 15β and αA/B were evaluated using the IEF-PCM model, and resulted in lower 15β and αA/B values likely due to the stabilization of the NOy molecules from dispersion interactions with water. Overall, our calculated 15β and αA/B values are accurate in the rigid rotor and harmonic oscillator approximations and will allow for the estimation of αA/B involving various NOy molecules. These calculated αA/B values may help to explain the trends observed in the N stable isotope ratio of NOy molecules in the atmosphere.

Impacts of potential CO2-reduction policies on air quality in the United States.

Impacts of emissions changes from four potential U.S. CO2 emission reduction policies on 2050 air quality are analyzed using the community multiscale air quality model (CMAQ). Future meteorology was downscaled from the Goddard Institute for Space Studies (GISS) ModelE General Circulation Model (GCM) to the regional scale using the Weather Research Forecasting (WRF) model. We use emissions growth factors from the EPAUS9r MARKAL model to project emissions inventories for two climate tax scenarios, a combined transportation and energy scenario, a biomass energy scenario and a reference case. Implementation of a relatively aggressive carbon tax leads to improved PM2.5 air quality compared to the reference case as incentives increase for facilities to install flue-gas desulfurization (FGD) and carbon capture and sequestration (CCS) technologies. However, less capital is available to install NOX reduction technologies, resulting in an O3 increase. A policy aimed at reducing CO2 from the transportation sector and electricity production sectors leads to reduced emissions of mobile source NOX, thus reducing O3. Over most of the U.S., this scenario leads to reduced PM2.5 concentrations. However, increased primary PM2.5 emissions associated with fuel switching in the residential and industrial sectors leads to increased organic matter (OM) and PM2.5 in some cities.

Examining single-source secondary impacts estimated from brute-force, decoupled direct method, and advanced plume treatment approaches

In regulatory assessments, there is a need for reliable estimates of the impacts of precursor emissions from individual sources on secondary PM2.5 (particulate matter with aerodynamic diameter less than 2.5 microns) and ozone. Three potential methods for estimating these impacts using Eulerian grid photochemical models are the brute-force (B–F) method, the decoupled direct method (DDM), and advanced plume treatment (APT). Here, we systematically inter-compare and assess the B–F, DDM, and APT approaches using hypothetical sources in a consistent modeling platform for a wide range of source conditions (i.e., emissions amount and composition, location within two California air basins, and stack parameters). The impacts of NOx and VOC sources on ozone and SO2 sources on PM2.5 sulfate calculated by these methods are in general agreement. The agreement is evident in the similar magnitudes, spatial patterns, and strong correlations among the impacts. This result, along with previous model evaluations based on similar Eulerian grid modeling, builds confidence in the reliability of the impact estimates. Disagreement among methods is evident in calculations of PM2.5 nitrate impacts associated with NH3 and NOx sources. Numerical instabilities in DDM sensitivity calculations compromise the nitrate impact estimates from that approach. The B–F and APT methods, which use brute-force differencing to identify impacts, are affected by numerical artifacts to a lesser degree than (H)DDM, with the artifacts being more prominent for APT than B–F. Overall, our results indicate that the (H)DDM, B–F, and APT approaches are viable for use in estimating single-source impacts for ozone and secondary PM2.5 sulfate, while the B–F method appears to be the most reliable for estimating nitrate impacts. There is a need for additional field study measurements to better constrain model estimates of single-source secondary impacts.

Use of isotopic compositions of nitrate in TSP to identify sources and chemistry in South China Sea

NO3− concentration, nitrogen and oxygen isotopic compositions (δ15N and δ18O) of NO3− were measured in total suspended particulates (TSP) at Yongxing Island in the South China Sea (SCS) between Feb. 2013 and Jan. 2014, as well as on two cruises in the northern South China Sea (NSCS). Measurements aimed to identify NO3− sources, and possible chemical formation processes of NO3−. The δ15N and δ18O of NO3− in TSP at Yongxing Island ranged from −2.5 to +4.9‰, and +48.1 to +99.0‰, with annual weighted averages of +1.5‰ and +83.2‰, respectively. Both δ15N and δ18O had higher values in cool months, indicating that NOx sources and oxidants were different between seasons. In cool months, NOx was mainly from anthropogenic sources, particularly from coal combustion in South China, resulting in high nitrogen deposition that was oxidized by O3 to NO3−. In warm months, natural emissions were an important source of NOx. TSP samples in the NSCS had higher NO3− concentrations, higher δ15N and lower δ18O values than samples from Yongxing Island over the same period. This suggests that atmospheric processes caused a decrease in NO3− concentrations and δ15N but increase in δ18O from coast to remote marine. Assuming to oxygen atoms were derived from O3 during transport in cool months, the mean ratio of NO3− formed by NOx to total NO3− was calculated to be 47.9%. This suggests the mean loss ratio of NOx was 89% while the loss ratio of NO3− was 87% during transport between Chinese coastal areas and Yongxing Island in Nov., 2013.

Do N-isotopes in atmospheric nitrate deposition reflect air pollution levels?

Dry and wet deposition of atmospheric reactive nitrogen compounds mostly originate from anthropogenic NH3 and NOX sources. Regarding land-borne pollutants, coastal environments usually have a lower pollution level than terrestrial/urban areas, which have a greater anthropogenic imprint. To investigate this spatial characteristic, we measured NO3− and NH4+ deposition and N isotopes of NO3− (δ15N–NO3−) in 94 and 88 wet and dry deposition samples, respectively, at a coastal (List on Sylt) and a terrestrial/urban site (Geesthacht) in Germany from May 2012 to May 2013. A higher total N deposition rate was observed in Geesthacht (10.4 vs. 8.9 kg N ha−1 yr−1) due to higher NH4+ deposition, which can be explained by more agricultural influence. Surprisingly, overall NO3− fluxes were higher at the coastal site than at the terrestrial/urban site. We assume that sea-salt aerosols and the increased influence of NOX emissions from ships in most recent times compensate the higher terrestrial/urban pollution level and thus lead to higher NO3− fluxes in dry and comparable fluxes in wet deposition at the coastal site, despite a much lower impact of land-based sources. In line with this, overall mean N isotopes values of NO3− show higher values in List than in Geesthacht in dry (+3.1 vs. +1.9‰) as well as in wet deposition (−0.1 vs. −1.0‰). This surprising result can mainly be attributed to an emerging source of NOX, ship emissions, which have a distinctly higher impact at the coastal site. The usage of heavy oil and possibly new technologies in marine engines, which emit more enriched 15N in comparison to older engines, caused the spatial isotopic differences.

Energy demand and vehicle emissions stimate in Aburra Valley from 2000 to 2010 using LEAP model

This article shows a retrospective analysis of energy demand and atmospheric pollution by urban transport in Aburra Valley, where Medellin is the main city. The study was carried out using LEAP model between 2000 and 2010, in order to generate information for defining strategies to help reduce air pollution in Aburra Valley. The results show that despite the rapid increase of vehicles, the energy demand and CO2 emissions grew slowly, while criteria pollutant emissions decreased during the last decade. Also, the study shows that during the modeled period trucks were an important source of CO, NOX, SOX and PM2.5. Motorcycles (2-cycles) were also important contributors to VOC vehicular emissions.

Nitrogen stable isotope composition (δ15N) of vehicle-emitted NOx.

The nitrogen stable isotope ratio of NOx (δ(15)N-NOx) has been proposed as a regional indicator for NOx source partitioning; however, knowledge of δ(15)N values from various NOx emission sources is limited. This study presents a detailed analysis of δ(15)N-NOx emitted from vehicle exhaust, the largest source of anthropogenic NOx. To accomplish this, NOx was collected from 26 different vehicles, including gasoline and diesel-powered engines, using a modification of a NOx collection method used by the United States Environmental Protection Agency, and δ(15)N-NOx was analyzed. The vehicles sampled in this study emitted δ(15)N-NOx values ranging from -19.1 to 9.8‰ that negatively correlated with the emitted NOx concentrations (8.5 to 286 ppm) and vehicle run time because of kinetic isotope fractionation effects associated with the catalytic reduction of NOx. A model for determining the mass-weighted δ(15)N-NOx from vehicle exhaust was constructed on the basis of average commute times, and the model estimates an average value of -2.5 ± 1.5‰, with slight regional variations. As technology improvements in catalytic converters reduce cold-start emissions in the future, it is likely to increase current δ(15)N-NOx values emitted from vehicles.

Influence of Coke Combustion on NOx Emission during Iron Ore Sintering

This paper explores NOx emission during iron ore sintering on a pilot-scale pot. A novel technique of using a three-layered bed structure was adopted to study the role of coke level, properties and combustion behavior on NOx emission. In addition, the lime content of the mix was also altered to understand the effect of the melt formation process. Thirteen sinter pot tests were employed to analyze the influence of coke combustion on NOx emission. As the flame front descended down the pot, NOx emission decreased because of increasing bed temperatures. For this reason, it is to be expected that increasing coke rate will result in higher sinter bed temperature and lower conversion of coke-N to NOx. However, overall NOx emission is little changed because more coke means higher N availability. Increasing basicity (CaO/SiO2) from 1.9 to 2.4 in raw mix results in the decrease of NOx emission, about 5%. Increasing coke size may result in the decrease or increase of NOx emission. Placing coke particles on the outside of granules can lower NOx emission in the middle and bottom layers, by 4–15%. NOx emission in the iron ore sinter process is determined by the conversion of coke-N to NOx and nitrogen source in sinter mix. The atmosphere around coke particles is very important for NOx reduction, and NOx emission will increase by around 15% when oxygen increases by 1 vol.%. During iron ore sintering, temperature has great influence on NOx emission, with levels decreasing by 15–25% for a 100 K temperature increase.