Reaction Of NO Research Articles

Mechanisms in the Catalytic Reduction of N2O by CO over the M13@Cu42 Clusters of Aromatic-like Inorganic and Metal Compounds.

Metal aromatic substances play a unique and important role in both experimental and theoretical aspects, and they have made tremendous progress in the past few decades. The new aromaticity system has posed a significant challenge and expansion to the concept of aromaticity. From this perspective, based on spin-polarized density functional theory (DFT) calculations, we systematically investigated the doping effects on the reduction reactions of N2O catalyzed by CO for M13@Cu42 (M = Cu, Co, Ni, Zn, Ru, Rh, Pd, Pt) core-shell clusters from aromatic-like inorganic and metal compounds. It was found that compared with the pure Cu55 cluster, the strong M-Cu bonds provide more structural stability for M13@Cu42 clusters. Electrons that transferred from the M13@Cu42 to N2O promoted the activation and dissociation of the N-O bond. Two possible reaction modes of co-adsorption (L-H) and stepwise adsorption (E-R) mechanisms over M13@Cu42 clusters were thoroughly discovered. The results showed that the exothermic phenomenon was accompanied with the decomposition process of N2O via L-H mechanisms for all of the considered M13@Cu42 clusters and via E-R mechanisms for most of the M13@Cu42 clusters. Furthermore, the rate-limiting step of the whole reactions for the M13@Cu42 clusters were examined as the CO oxidation process. Our numerical calculations suggested that the Ni13@Cu42 cluster and Co13@Cu42 clusters exhibited superior potential in the reduction reactions of N2O by CO; especially, Ni13@Cu42 clusters are highly active, with very low free energy barriers of 9.68 kcal/mol under the L-H mechanism. This work demonstrates that the transition metal core encapsulated M13@Cu42 clusters can present superior catalytic activities towards N2O reduction by CO.

A new insight into the vertical differences in NO2 heterogeneous reaction to produce HONO over inland and marginal seas

Abstract. Ship-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements were conducted along the marginal seas of China from 19 April to 16 May 2018 to measure the vertical profiles of aerosol, nitrogen dioxide (NO2), and nitrous acid (HONO). Along the cruise route, we found five hot spots with enhanced tropospheric NO2 vertical column densities (VCDs) in the Yangtze River Delta, Taiwan Strait, Guangzhou–Hong Kong–Macau Greater Bay Area, port of Zhanjiang, and port of Qingdao. Enhanced HONO concentrations could usually be observed under high-level aerosol and NO2 conditions, whereas the reverse was not always the case. To understand the impacts of relative humidity (RH), temperature, and aerosol on the heterogeneous reaction of NO2 to form HONO in different scenarios, the Chinese Academy of Meteorological Sciences (CAMS) and Southern University of Science and Technology (SUST) MAX-DOAS stations were selected as the inland and coastal cases, respectively. The RH turning points in CAMS and SUST cases were both ∼ 65 % (60 %–70 %), whereas two turning peaks (∼ 60 % and ∼ 85 %) of RH were found in the sea cases. As temperature increased, the HONO / NO2 ratio decreased with peak values appearing at ∼ 12.5∘C in CAMS, whereas the HONO / NO2 gradually increased and reached peak values at ∼ 31.5∘C in SUST. In the sea cases, when the temperature exceeded 18.0∘C, the HONO / NO2 ratio rose with increasing temperature and achieved its peak at ∼ 25.0∘C. This indicated that high temperature can contribute to the secondary formation of HONO in the sea atmosphere. In the inland cases, the correlation analysis between HONO and aerosol in the near-surface layer showed that the ground surface is more crucial to the formation of HONO via the heterogeneous reaction of NO2; however, in the coastal and sea cases, the aerosol surface contributed more. Furthermore, we discovered that the conversion rate of NO2 to HONO through heterogeneous reactions in the sea cases is larger than that in the inland cases in higher atmospheric layers (> 600 m). Three typical events were selected to demonstrate three potential contributing factors of HONO production under marine conditions (i.e., transport, NO2 heterogeneous reaction, and unknown HONO source). This study elucidates the sea–land and vertical differences in the forming mechanism of HONO via the NO2 heterogeneous reaction and provides deep insights into tropospheric HONO distribution, transforming process, and environmental effects.

Atmospheric chemistry of 2-nitrobenzaldehyde: Initiated by photo-excitation, OH-oxidation, and small TiO2 clusters adsorption catalysis

The fate of 2-nitrobenzaldehyde (2-NBA) is of interest in atmospheric chemistry as it is a semi-volatile organic compound with high photosensitivity. This study presents a quantum chemical study of the gas-phase reactions of 2-NBA photo-excitation and OH-oxidation in the absence and presence of small TiO2 clusters. To further understand the unknown photolysis mechanism, the photo-reaction pathways of ground singlet state and the lying excited triplet state of 2-NBA were investigated including the initial and subsequent reactions of proton transfer, direct CO, NO2, and HCO elimination routes in the presence of O2 and NO. Meanwhile, the OH-mediated degradation of 2-NBA proceeded via five H-extraction and six OH-addition channels by indirect mechanism, which follows a succession of reaction steps initiated by the formation of weakly stable intermediate complexes. The H-extraction from the –CHO group was the dominant pathway with a negative activation energy of -1.22 kcal/mol. The calculated rate coefficients at 200–600 K were close to the experimental data in literature within 308–352 K, and the kinetic negative temperature independence was found in both experimental literature and computational results. Interestingly, 2-NBA was favored to be captured onto small TiO2 clusters via six adsorption configurations formed via various combination of three types of bonds of Ti···O, Ti···C, and O···H between the molecularly adsorbed 2-NBA and TiO2 clusters. Comparison indicted that the chemisorptions of aldehyde oxygen have largest energies. The results suggested adsorption conformations have a respectable impact on the catalysis barrier. This study is significant for understanding the atmospheric chemistry of 2-nitrobenzaldehyde.

Numerical analysis and flamelet modeling of NO[formula omitted] formation in a thermodiffusively unstable hydrogen flame

In a thermodiffusively unstable premixed hydrogen flame, cellular flame structures exist due to the strong differential diffusion of hydrogen featuring wide ranges of curvature and strain rate. NOx formation pathways are directly affected by the complex cellular flame structures as different species have different sensitivities to differential diffusion effects and curvature. In this work, the NOx formation characteristics of a thermodiffusively unstable laminar premixed hydrogen flame are investigated. At first, the NOx formation characteristics in the tangential and normal directions of the flame front are analyzed, focusing on the effects of curvature. Then, reaction path analyses are conducted to identify the relevant pathways and elementary reactions that pre-dominantly contribute to the formation of NOx pollutants. To investigate the effects of curvature on NOx formation, the reaction fluxes and the elementary reaction rates are calculated by conditioning on the curvature value. Finally, the performance of a flamelet model in predicting the NOx species in the thermodiffusively unstable premixed hydrogen flame is evaluated through an a priori analysis. The results show that curvature directly affects NOx formation, particularly the dominant NNH and N2O reaction pathways while the contribution of the thermal-NO pathway is found to be overall negligible. The NOx species are mainly formed in positively-curved flame segments where the flamelet model gives good predictions, while discrepancies with respect to the model exist in the negatively-curved flame regions. The reason for this is clarified through a chemical timescale analysis and a conditional reaction path analysis.

Study of NO emission from CH4-air, oxygen-enriched, and oxy-CH4 combustion under HTC and MILD regimes: Impact of wall thermal condition in different oxidant temperature and dilution level

The present work investigates the effect of wall thermal conditions on the NO emission in the different inlet temperatures and oxidant dilution levels. The studies are performed for the CH4-air, oxygen-enriched, and oxy-CH4 combustion under the HTC and MILD regimes by numerical simulation of the non-premixed furnace and chemical calculations of the WSR reactor. It is found that higher heat loss from the wall and more replacement of CO2 with N2 facilitate the establishment of the MILD regime and significant reduction of NO production. The results show an optimum point for achieving the minimum heat loss and NO emission. Under the MILD regime, dominant mechanisms in the NO emission are prompt through reaction CH + N2⇌HCN + N and thermal routes for the CH4-air condition and N2O-intermediate by reactions N2O + O⇌2NO and N2O + H⇌N2+OH and thermal mechanisms for oxy-CH4 combustion. In both atmospheres, the thermal route plays the main role in the low heat loss from walls, while other routes are more active in the low maximum flame temperature. Reaction N + NO⇌N2+O by supplying O radical from reactions O + CO + M⇌CO2+M and H + O2+M⇌HO2+M is activated by increasing O2 level, while reactions N + NO⇌N2+O and N + OH⇌NO + H show the main contribution in the sensitivity analysis of NO.

Aging of pollution air parcels acts as the dominant source for nocturnal HONO

Atmospheric HONO acts as a major source for OH radicals in polluted areas, playing an important role in formation of secondary pollutants. However, the atmospheric HONO sources remain unclear. Here we propose that the heterogeneous reaction of NO2 on aerosols during aging processes acts as the dominant source for nocturnal HONO. Based on the nocturnal variations of HONO and related species in Tai'an city of China, we firstly developed new method to estimate the localized HONO dry deposition velocity (v(HONO)). The estimated v(HONO) of 0–0.077 m/s was in a good agreement with the reported ranges. Additionally, we set up a parametrization to reflect the HONO formation from the aged air parcels based on the variation of HONO/NO2 ratio. The detailed variation of nocturnal HONO could be well reproduced by a complete budget calculation coupled with above parameterizations, with the difference between the observed and calculated HONO levels being <5 %. The results also revealed the average contribution of HONO formation from aged air parcels to atmospheric HONO could achieve to be ~63 % in average.

Experimental and kinetic study of N2O thermal decomposition in pressurized oxy-combustion

Pressurized oxy-combustion is regarded as a promising carbon capture technology for mitigating global warming. In addition, N2O is a significant greenhouse gas in pressurized oxy-combustion at moderate temperatures, with a Global Warming Potential 310 times that of CO2. It is important to study the formation and control of N2O in pressurized oxy-combustion. In this paper, the effects of CO2 atmosphere, pressure, temperature, residence time, and O2 concentration on N2O decomposition were investigated in a pressurized plug flow reactor. The results show that CO2 atmosphere significantly promotes N2O decomposition compared to N2 atmosphere. Increasing temperature accelerates the decomposition of N2O, with 1023–1223 K being the main decomposition temperature range. The decomposition efficiency of N2O increases with increasing pressure, while its increase becomes slow at above 5 bar. N2O decomposition efficiency in CO2 atmosphere decreases slightly as O2 concentration increases. The experimental results were compared to the kinetic modeling results calculated using GRI3.0 and GLA2018 mechanism, respectively. The modeling results show that GRI3.0 mechanism accurately predicts the decomposition of N2O at 1 bar while overestimates the decomposition at elevated pressures, while GLA2018 mechanism significantly underestimates the decomposition at all tested pressures. Further Rate-of-production analysis shows that the main reaction of N2O decomposition is N2O(+M) = N2 + O + M, which becomes the dominant reaction especially at elevated pressures. An enhanced third-body efficiency of 3 for CO2 was incorporated into the reaction N2O(+M) = N2 + O(+M) in GLA2018, which could predict the decomposition of N2O at elevated pressure accurately. The above results indicate that the decomposition of N2O is significantly enhanced in pressurized oxy-combustion.

Nitrate chemistry in the northeast US – Part 1: Nitrogen isotope seasonality tracks nitrate formation chemistry

Abstract. Despite significant precursor emission reductions in the US over recent decades, atmospheric nitrate deposition remains an important terrestrial stressor. Here, we utilized statistical air mass back trajectory analysis and nitrogen stable isotope deltas (δ(15N)) to investigate atmospheric nitrate spatiotemporal trends in the northeastern US from samples collected at three US EPA Clean Air Status and Trends Network (CASTNET) sites from December 2016–2018. For the considered sites, similar seasonal patterns in nitric acid (HNO3) and particulate nitrate (pNO3) concentrations were observed with spatial differences attributed to nitrogen oxide (NOx) emission densities in source contributing regions that were typically ≤ 1000 km. Significant spatiotemporal δ(15N) variabilities in HNO3 and pNO3 were observed with higher values during winter relative to summer, like previous reports from CASTNET samples collected in the early 2000s for our study region. In the early 2000s, δ(15N) of atmospheric nitrate in the northeast US had been suggested to be driven by NOx emissions; however, we did not find significant spatiotemporal changes in the modeled NOx emissions by sector and fuel type or δ(15N, NOx) for the source regions of the CASTNET sites. Instead, the seasonal and spatial differences in the observed δ(15N) of atmospheric nitrate were driven by nitrate formation pathways (i.e., homogeneous reactions of NO2 oxidation via hydroxyl radical or heterogeneous reactions of dinitrogen pentoxide on wetted aerosol surfaces) and their associated δ(15N) fractionation. Under the field conditions of low NOx relative to O3 concentrations and when δ(15N, NOx) emission sources do not have significant variability, we demonstrate that δ(15N) of atmospheric nitrate can be a robust tracer for diagnosing nitrate formation.

Heterogeneous catalytic reaction of NO2 to HONO on hematite

The heterogenous catalytic reactions of NO2 on mineral dusts represent one of the important sources of HONO that promote the formation of O3 and other air pollutants, but the mechanism is poorly understood. First principles calculations, including a Hubbard-like +U correction and a dispersion correction, were employed to investigate the heterogeneous interaction of NO2 on the hematite (0001) surface. The competitive adsorption between the most common gas molecules in polluted air (NO2, CO, SO2, O3, H2O, O2, and N2) were also investigated. Under dry conditions, the (NO3δ−)(NOδ+) intermediate species can transform into surface NO3 and gaseous NO. Under wet conditions, the simulations predicted the production of HONO and HNO3 through the hydrolysis of NO2 via (NO3δ−)(NOδ+). Adsorption energies show that the surface Fe site provides strong interactions. Charge transfer occurs from the Fe atom to the adsorbate molecules. This study may facilitate the understanding of the transformations of the atmospheric gas pollutants on naturally occurring mineral dust aerosols. The heterogenous reaction may impact on global atmospheric chemistry.

Chemical drivers of ozone change in extreme temperatures in eastern China

Surface ozone pollution has become the biggest issue in China's air pollution since particulate matters have been improved in the atmosphere. Compared with normal winter/summer, extremely cold/hot weather sustained several days and nights by unfavorable meteorology is more impactful in this regard. However, ozone changes in extreme temperatures and their driving processes remain rarely understood. Here, we combine comprehensive observational data analysis and 0-D box models to quantify the contributions of different chemical processes and precursors to ozone change in these unique environments. Analyses of radical cycling indicate that temperature accelerates OH–HO2–RO2, optimizing ozone production efficiency in higher temperatures. The HO2 + NO → OH + NO2 reaction was the most influenced by temperature change, followed by OH + VOCs → HO2/RO2. Although most reactions in ozone formation increased with temperature, the increase in ozone production rates was greater than the rate of ozone loss, leading to a fast net ozone accumulation in heat waves. Our results also show that the ozone sensitivity regime is VOC-limited in extreme temperatures, highlighting the significance of volatile organic compound (VOC) control (particularly the control of alkenes and aromatics). In the context of global warming and climate change, this study helps us deeply understand ozone formation in extreme environments and design abatement policies for ozone pollution in such conditions.

Low-temperature NOx capture and reduction via NO oxidation by O3 on Cu-CHA

We studied the transient reduction of NOx with NH3 over Cu-exchanged CHA zeolite (Cu-CHA) assisted by the catalyst-free oxidation of NO by O3. The room-temperature catalyst-free oxidation of NO by O3 yielded NO2 at low O3/NO ratio and N2O5 as the main product at higher ratios. DFT calculations verified the reaction of NO2 +O3 to N2O5 proceeding with low activation energies. Transient operando IR measurements demonstrated that Cu-CHA exposure to NO+O3 at 100 °C resulted in the storage of NOx as NO3− on the Cu2+ site. The stored NOx reacted with NH3 to yield N2 and NH4NO3. Preadsorbed NH3 on Cu-CHA was oxidized by O3 to yield N2 and N2O. The reaction of preadsorbed NH3 with NO+O3 caused the selective formation of N2. The obtained results may aid in developing a new O3-assisted unsteady-state lean De-NOx process involving reactions of captured NOx with NH3 or reduction of NOx with stored NH3.

Effect of Intermediate Radicals on NOx and De‐NOx Characteristics of NH3/H2/Air Flames at High Pressure

AbstractThe effect of NH, NH2, and HNO on NOx and De‐NOx chemistry of a NH3/H2/air mixture at a pressure of 20 bar is investigated. Results suggest that the increase in pressure reduces NOx emissions and increases HO2 radical production through the reaction H + O2(+M) → HO2(+M). In contrast with OH and O radicals, the HO2 radical is less reactive, which prevents NO formation. The fuel‐bound NOx emissions mainly depend on the reactions NH + OH → NO + H, HNO(+M) → NO + H(+M), HNO + OH → NO + H2O, and HNO + O2 → NO + HO2, and thermal NOx depends on the reactions N + O2 → NO + N and N + OH → NO + H. At a pressure of 20 bar, the N2O is further converted to NO2 and N2 through the reaction N2O + NO → NO2 + N2. The abundance of HO2 radicals at high pressure also initiates the conversion of NO to NO2 via the reaction NO + HO2 → NO2 + H.

Intercomparison of NO3 under Humid Conditions with Open-Path and Extractive IBBCEAS in an Atmospheric Reaction Chamber

We report an open-path incoherent broadband cavity-enhanced absorption spectroscopy (OP-IBBCEAS) technique for in situ simultaneous optical monitoring of NO2, NO3, and H2O in a reaction chamber. The measurement precision values (1σ) are 2.9 ppbv and 2.9 pptv for NO2 and NO3 in 2 s, respectively, and the measurement uncertainties are 6% for NO2 and 14% for NO3. Intercomparison of measured concentrations of NO2 and NO3 by open-path and extractive IBBCEAS was carried out in the SAES-ARC reaction chamber during the reaction of NO2 with O3. The measurement accuracy of OP-IBBCEAS is verified by an NO2 intercomparison and the NO3 transmission efficiency of the extractive IBBCEAS is determined by comparison against the in situ NO3 measurement. The relationship between H2O absorption cross section and its mixing ratio at 295 K and 1 atm was analysed. Due to the spectral resolution of IBBCEAS system, the strong and narrow absorption lines of H2O are unresolved and exhibit non-Beer–Lambert Law behaviour. Therefore, a correction method is used to obtain the effective absorption cross section for fitting the H2O structure. An inappropriate H2O absorption cross section can cause an overestimation of NO3 concentration of about 28% in a humid atmosphere (H2O = 1.8%). This spectroscopic correction provides an approach to obtain accurate NO3 concentrations for open-path optical configurations, for example in chamber experiments or field campaigns. The measurement precision values are improved by a factor of 3 to 4 after applying Kalam filtering, achieving sub-ppbv (0.8 ppbv) and sub-pptv (0.9 pptv) performance in 2 s for NO2 and NO3, respectively.

On the role of HNNO in NO[formula omitted] formation

The formation of nitrogen oxides (NOx) during combustion is a topic of substantial fundamental and practical interest, given the complex nature of its formation kinetics and the fact that, as a highly regulated pollutant emission, it is a major constraint in engineering design. To date, there are four known mechanisms by which the strong N–N bond can be broken to facilitate NOx formation from N2 present in air. Here we posit and explore the possibility of a new NOx formation route mediated by an HNNO intermediate whose reactions with common combustion species break the N–N bond. Altogether, we present results from master equation (ME) calculations for HNNO formation from H + N2O (+M), ab initio electronic structure and RRKM/ME calculations for HNNO + O2, and simulations of NO profiles in freely propagating flames using a newly constructed HNNO kinetic sub-model. Our ME results for the H + N2O reaction indicate that HNNO is the favored product channel at lower temperatures and higher pressures – e.g. favored over all other products up to ∼1100 K and over NH + NO up to ∼1500 K above 10 atm. Our ab initio electronic structure calculations for trans-HNNO + O2 show a barrier for abstraction to HO2 + N2O of 18.2 kcal/mol and a barrier for addition of 27.0 kcal/mol to form an HN(OO)NO which can decompose to NO + HNO2 over a barrier of 32.3 kcal/mol (cis-HNNO + O2 shows similar reactivity). Altogether, our rate constant calculations and kinetic modeling, which also includes estimated rate constants for HNNO + radical reactions, suggest that HNNO + O2 mainly recycles HNNO back to N2O but is sufficiently slow that the primary fate of HNNO in many combustion situations likely involves reactions with radical species, which appear likely to occur quickly and with high NOx yields.

A theoretical study of the gas-phase reactions of propadiene with NO3: mechanism, kinetics and insights.

In this study, the conversion mechanisms and kinetics of propadiene (CH2[double bond, length as m-dash]C[double bond, length as m-dash]CH2) induced by NO3 were researched using density functional theory (DFT) and transition state theory (TST) measurements. The NO3-addition pathways to generate IM1 (CH2ONO2CCH2) and IM2 (CH2CONO2CH2) play a significant role. P3 (CH2CONOCHO + H) was the dominant addition/elimination product. Moreover, the results manifested that one H atom from the -CH2- group has to be abstracted by NO3 radicals, leading to the final product h-P1 (CH2CCH + HNO3). Due to the high barrier, the H-abstraction pathway is not important for the propadiene + NO3 reaction. In addition, the computed ktot value of propadiene reacting with NO3 at 298 K is 3.34 × 10-15 cm3 per molecule per s, which is in accordance with the experimental value. The computed lifetime of propadiene oxidized by NO3 radicals was assessed to be 130.16-6.08 days at 200-298 K and an altitude of 0-12 km. This study provides insights into the transformation of propadiene in a complex environment.

Comment on "Theoretical study of the NO3 radical reaction with CH2ClBr, CH2ICl, CH2BrI, CHCl2Br, and CHClBr2" by I. Alkorta, J. M. C. Plane, J. Elguero, J. Z. Dávalos, A. U. Acuña and A. Saiz-Lopez, Phys. Chem. Chem. Phys. 2022, 24, 14365.

This comment addresses a systematic error in the potential energy surfaces of the title reactions presented in the original article by Alkorta et al. The NO3 radical has D3h symmetry in the electronic ground state while the M08HX functional employed in the original article predicts an incorrect C2v geometry and energy. By combining thermodynamic data for the OH + HNO3 → H2O + NO3 reaction with spectroscopic data and results from M08HX calculations on HNO3, H2O and the OH radical, the ground state NO3 radical energy is estimated to be 37 kJ mol-1 lower than reported for the C2v geometry.

Pyrolysis and oxidation of benzene and cyclopentadiene by NOx: a ReaxFF molecular dynamics study.

Benzene (C6H6) and 1,3-cyclopentadiene (c-C5H6) are critical intermediate species in the combustion of fossil fuel and the formation of polycyclic aromatic hydrocarbons (PAHs). This study investigates the underlying mechanisms of pyrolysis and oxidation of C6H6 and c-C5H6 in the presence of O2, NO and NO2, respectively, under combustion conditions via ReaxFF molecular dynamics simulations. The size growth in the pyrolysis system is accompanied by an amorphous nature as well as an increase in the C/H ratio. In the oxidation sytems, NO2 is the most effective in the oxidation of both C6H6 and c-C5H6, followed by NO and O2. In the presence of NOx, O and N radicals generated in the high-temperature decomposition reactions of NO and NO2 are actively involved in the addition and H-abstraction reactions of C6H6 and c-C5H6. Remarkably, the decomposition of NO2 dramatically increases the number of O radicals in the system, which significantly accelerates the ring-opening of C6H6 and c-C5H6 by O-addition and forms linear-C6H6O and C5H6O species, respectively. Afterwards, the formation of -CH2- by H-transfer plays an essential role in the decomposition of linear-C6H6O and -C5H6O. Reaction pathways of O and N radicals with C6H6 and c-C5H6 are reported in detail. The O and N-addition of C6H6 facilitate the decomposition to resonance-stabilized cyclopentadienyl radicals after the restructuring of the C-C bond.

Reply to the 'Comment on "Theoretical study of the NO3 radical reaction with CH2ClBr, CH2ICl, CH2BrI, CHCl2Br, and CHClBr2"' by C. J. Nielsen and Y. Tang, Phys. Chem. Chem. Phys., 2022, 24, DOI: 10.1039/D2CP03013F.

In this Reply, we answer the main argument raised in the Comment about the energy of the NO3 radical and its influence in the reaction profiles of the reaction of the NO3 radical with CH2ClBr, CH2ICl, CH2BrI, CHCl2Br, and CHClBr2 by C. J. Nielsen and Y. Tang. The optimized geometry of the NO3 radical has been obtained using 49 DFT functionals: 26 functionals predict a minimum with D3h symmetry and 23 with C2v symmetry. The former functionals have been used to calculate the thermodynamic values of three reactions (X + HNO3 → XH + NO3, X= OH, CH3 and CCl3) and compared with experimental data. Those functionals with smaller errors have been used to recalculate the barriers of the reaction of NO3 with CH2ClBr, CH2ICl, CH2BrI, CHCl2Br, and CHClBr2. The results show differences of 10.5 kJ mol-1 when compared to those obtained with the M08HX functional.

NO3 reactivity measurements in an indoor environment: a pilot study

First indoor NO3 reactivity measurement confirms that NO3 is a significant indoor oxidizing agent.

Colorimetric and fluorogenic detection of nitrite anion in water and food based on Griess reaction of fluorene derivatives

New Griess reagents for nitrite determination were developed using two fluorene derivatives; 2-amino-7-bromofluorene (ABF) and 2-amino-7-bromo-9,9-dimethylfluorene (ABDF). The system of ABF is colorimetric sensor while the ABDF system is a dual-mode colorimetric and fluorogenic sensor. The diazotization reaction of ABF, NO2-, and β-naphthol in acid solution provided azo-dye product and led to an obvious color change from colorless to pink. The same reaction with ABDF displayed the color change to pink and a fluorescence quenching of ABDF emission. Under the optimal condition, colorimetric response, fluorogenic response, anion competition and detection limitation toward NO2- were determined using naked eye observation, UV-Vis and fluorescence technique. The lowest LOD (0.0007 mg L-1) was obtained from fluorescent method of ABDF. In addition, nitrite anion in different ham types were successfully analyzed using ABDF and fluorescent method which presented satisfactory performance parameters such as working range (0.0024 – 0.020 mg L-1), %recovery (83.36–107.68) and %RSD (0.26–3.77). According to paired t-test at a 95% confidence level, there was no significant differences between the results from the ABDF and those from the reference method. The practical application of ABF/ABDF sensors based on hydrogel indicator can be used for on-site monitoring of NO2- with a high sensitivity and selectivity by showing the same results of naked-eye color change and fluorescence turning off.