Abiotic mechanism for the formation of atmospheric nitrous oxide from ammonium nitrate

Nitrous oxide (N2O) is an important greenhouse gas and a primary cause of stratospheric ozone destruction. Despite its importance, there remain missing sources in the N2O budget. Here we report the formation of atmospheric nitrous oxide from the decomposition of ammonium nitrate via an abiotic mechanism that is favorable in the presence of light, relative humidity and a surface. This source of N2O is not currently accounted for in the global N2O budget. Annual production of N2O from atmospheric aerosols and surface fertilizer application over the continental United States from this abiotic pathway is estimated from results of an annual chemical transport simulation with the Community Multiscale Air Quality model (CMAQ). This pathway is projected to produce 9.3(+0.7/-5.3) Gg N2O annually over North America. N2O production by this mechanism is expected globally from both megacities and agricultural areas and may become more important under future projected changes in anthropogenic emissions.     

宁德市大气臭氧污染现状及影响因素

以宁德市蕉城区农机局、市监测站国控监测点2016年1月到2017年7月臭氧8小时监测值为基础,研究臭氧浓度的日变化、月变化趋势及臭氧相关影响因素,结果表明:在高温、低湿、低风速、晴朗无云的情况下,易形成高浓度臭氧;低温、高湿、少日照不利于臭氧的生成.现实情况中可能存在跨区域输送或区域内生成等情况都会导致臭氧污染的生成不...     

Effects of atmospheric cold plasma and ozone on prebiotic orange juice

In this study, the effect of plasma and ozone treatments on the quality of orange juice was evaluated. The juice was directly and indirectly exposed to a plasma field at 70 kV for different treatment times: 15, 30, 45 and 60 s. For ozone processing, different loads (0.057, 0.128 and 0.230 mg/O₃ mL of juice) were evaluated. After the treatments, the oligosaccharides were quantified by HPLC. The juice pH, color, total phenolic content and total antioxidant activity were also determined. Both processes promoted a partial degradation of the oligosaccharides in the juice. However, the juice maintained an enough amount of oligosaccharides to be classified as a prebiotic food. The phenolic content and antioxidant capacity of the treated samples was also well preserved as the pH and color. Thus, atmospheric cold plasma and ozone are suitable non-thermal alternatives for prebiotic orange juice treatment.Industrial relevanceConsumers are looking for safe food products with high quality. Thus, the food industry is currently considering non-thermal processes as an alternative to reduce the nutrient loss in processed foods. Despite atmospheric cold plasma and ozone are technologies already evaluated as an efficient non-thermal alternative for pathogens inactivation in orange juice, no previous studies on their effects on the oligosaccharides in functional fruit juice was published. This study is of industrial relevance because it demonstrates that after plasma and ozone treatment the overall quality of prebiotic orange juice was preserved and the product maintained its functional appeal.     

Rate constants for the gas-phase reactions of a series of alkylnaphthalenes with the nitrate radical

Naphthalene and its methyl-, ethyl-, and dimethyl-derivatives are semivolatile polycyclic aromatic hydrocarbons expected to be in the gas phase in ambient atmospheres and are subject to nighttime degradation by gas-phase reactions with the nitrate (NO3) radical. Using a relative rate method, rate constants for the gas-phase reactions of NO3 radicals with a series of alkylnaphthalenes have been measured at 298 +/- 2 K and atmospheric pressure of air. The compounds studied were 1- and 2-methylnaphthalene (1- and 2-MN), 1- and 2-ethylnaphthalene (1- and 2-EN), and the 10 dimethylnaphthalene isomers (1,2-, 1,3-, 1,4-,1,5-, 1,6-, 1,7-, 1,8-, 2,3-, 2,6-, and 2,7-DMN). Sampling in Riverside, CA showed that these alkylnaphthalenes were readily detected in ambient air, with the exception of 1,8-DMN. The reactions of naphthalene and the alkylnaphthalenes with NO3 radicals proceed by initial addition of the radical to form an aromatic-NO3 adduct (with rate constant k(a)) which either decomposes back to reactants (with rate constant kb) or reacts with NO2 to form products (with rate constant k(c). Using naphthalene as the reference compound, the values of (k(a)k(c)/k(b)) obtained for the NO3 radical reactions (in units of 10(-28) cm(6) molecule(-2) S(-1), indicated errors are two least-squares standard deviations) were as follows: 1-MN, 7.15 +/- 0.37; 2-MN, 10.2 +/- 1.0; 1-EN, 9.82 +/- 0.69; 2-EN, 7.99 +/- 0.99; 1,2-DMN, 64.0 +/- 2.3; 1,3-DMN, 21.3 +/- 1.2; 1,4-DMN, 13.0 +/- 0.5; 1,5-DMN, 14.1 +/- 1.3; 1,6-DMN, 16.5 +/- 1.8; 1,7-DMN, 13.5 +/- 0.7; 1,8-DMN, 212 +/- 59; 2,3-DMN, 15.2 +/- 0.5; 2,6-DMN, 21.2 +/- 1.6; 2,7-DMN, 21.0 +/- 1.5.     

Analytical methods for nitrate and nitrite in feeds. 1. Spectrophotometric determination of nitrate with o-cresol]

The o-cresol procedure which is used for determining nitrate in feeds is tested for precision. The treatment of the samples and the course of analysis are rationalized. The method is recommended as a standard procedure for biological materials; it is suited as a reference technique in elaborating new analytical procedures.     

Analysis of atmospheric sesquiterpenes: sampling losses and mitigation of ozone interferences

Atmospheric standards containing parts-per-billion levels of 14 semivolatile hydrocarbon compounds, including eight sesquiterpenes (SQTs) (longipinene, alpha-copaene, isolongifolene, alpha-cedrene, trans-caryophyllene, aromadendrene, alpha-humulene, delta-cadinene), two oxidized sesquiterpenoids (cisnerolidol, trans-nerolidol), one biogenic ketone (geranylacetone) and three aromatic compounds (1,3,5-triisopropylbenzene, diphenylmethane, nonylbenzene), were collected onto four solid adsorbent materials at increasing ozone mixing ratios (0-100 ppbv 03) for analysis by thermodesorption-gas chromatography. Substantial sampling losses of up to >90% were found for the most reactive SQT, even at the lowest ozone level investigated of 20 ppbv. Loss rates from the ozone-SQT reaction were used to derive estimates of gas-phase ozone reaction rate constants for longipinene, alpha-copaene, isolongifolene, geranylacetone, aromadendrene, delta-cadinene, cis-nerolidol, and transnerolidol. Three different ozone mitigation techniques were investigated to prevent these sampling losses. These strategies included (a) placing glass fiber filters impregnated with sodium thiosulfate (Na2S2O3) into the sampling line, (b) titration of ozone in the sampling stream with nitric oxide (NO), and (c) catalytically removing ozone with a commercially available manganese dioxide (MnO2) catalyst. All three techniques reduced ozone-mixing ratios from 100 ppbv to <0.6 ppbv at sampling flow rates of 1 L min(-1). When the Na2S2O3 filters and the NO-titration techniques were applied, SQT loss rates decreased from 25-60% to 0-5% for most SQT compounds and from >90% to approximately 10-50% for the two most reactive compounds at ozone mixing ratios of up to 100 ppbv. The commercial manganese dioxide scrubber, however, caused complete analyte losses (>98%) even at 0 ppbv ozone. These results underline the need and present applicable techniques for removal of ozone in air samples for SQT analysis by solid adsorption techniques.     

Understanding nitrate reactions with zerovalent iron using tafel analysis and electrochemical impedance spectroscopy

This study investigated the reaction mechanisms of nitrate (NO3-) with zerovalent iron (ZVI) media under conditions relevantto groundwatertreatment using permeable reactive barriers (PRB). Reaction rates of NO3- with freely corroding and with cathodically or anodically polarized iron wires were measured in batch reactors. Tafel analysis and electrochemical impedance spectroscopy (EIS) were used to investigate the reactions occurring on the iron surfaces. Reduction of NO3- by corroding iron resulted in near stoichiometric production of NO2-, which did not measurably react in the absence of added Fe(II). Increasing NO3- concentrations resulted in increasing corrosion currents. However, EIS and Tafel analyses indicated that there was little direct reduction of NO3- at the ZVI surface, despite the presence of water reduction. This behavior can be attributed to formation of a microporous oxide on the iron surfaces that blocked reduction of NO3- and NO2- but did not block water reduction. This finding is consistent with previous observations that NO3- impedes reduction of organic compounds by ZVI. Nitrite concentrations greater than 4 mM resulted in anodic passivation of the iron, but passivation was not observed with NO3- concentrations as high as 96 mM. This indicates that the passivating oxide preventing NO3- reduction was permeable toward cation migration. Since reaction with Fe(0) can be excluded asthe mechanism for NO3- and NO2- reduction, reaction with Fe(II)-containing oxides coating the iron surface is the most likely reaction mechanism. This suggests that short-term batch tests requiring little turnover of reactive sites on the iron surface may overestimate long-term rates of NO3- removal because the effects of passivation are not apparent in batch tests conducted with high initial Fe(II) to NO3- ratios.     

Performance and simulation of ozone absorption and reactions in a stirred-tank reactor

This research investigates the mass transport of gaseous ozone accompanied by decomposition and ozonation reactions in the liquid phase. Absorption experiments were carried out under semibatch mode by continued injection of gaseous ozone into an agitated vessel containing an aqueous solution of 2,4- or 2,6-dichlorophenol at 25 degrees C. Under the influence of a fast reaction between the dissolved ozone and dichlorophenol, the mass transfer rate of ozone is enhanced greatly resulting in rapid destruction of the dichlorophenol. Simulations of the experimental results suggest that the complete mixing model can be applied to describe the fluid flow patterns in both the gas and liquid phases. The results of this study indicate that dichlorophenols can be removed effectively from aqueous solutions of pH near neutrality and that there is little additional advantage in carrying out the treatment process in alkaline solutions.     

Analysis of nitrate and nitrite in feed. 2. Potentiometric nitrate determination with ion sensitive electrodes]

Nitrate-sensitive PVC matrix membrane electrodes produced in the German Democratic Republic are suited for determining nitrates in feeds and plants if the different causative parameters are taken into account. A rational determining method is presented. Comparisons with the o-cresol method showed statistically confirmed agreement.     

Oxidation of atmospheric humic like substances by ozone: a kinetic and structural analysis approach

This work explores the heterogeneous reaction between HUmic-LIke Substances (so-called HULIS) and ozone. Genuine atmospheric HULIS were extracted from aerosol samples collected in Chamonix (France) in winter and used in coated flow tube experiments to evaluate heterogeneous uptake of O? on such mixtures. The uptake coefficient (γ) was investigated as a function of pH (from 2.5 to 10), O? concentration (from 8 to 33 × 1011 molecules cm?3), relative humidity (20 to 65%) and photon flux (from 0 to 1.66 × 101? photons cm?2 s?1). Reactive uptake was found to increase in the irradiated experiment with pH, humidity and photon flux. The extract was characterized before and after exposure to O? and/or UV light in the attempt to elucidate the effect of the photochemical aging. Carbon content measurements, UV-vis spectroscopy and functional groups analysis revealed a decrease of the UV absorbance as well as of the carbon mass content, while the functionalization rate (COOH and C═O) and therefore the polarity increased during the simulated photochemical exposure.     

血清铁蛋白化学发光免疫分析方法的建立及临床应用

利用链霉亲和素-生物素放大系统及双抗夹心法,建立检测血清铁蛋白的化学发光免疫分析方法。将生物素、辣根过氧化物酶分别标记铁蛋白的一对抗体,以链霉亲和素包被96孔发光板,铁蛋白标准品与国际标准品进行溯源,并对本法的各项性能指标进行评价。收集300份临床血清样本,使用本法与进口试剂盒同时检测,检测结果显示:相关系数r为0.97,本法的线性测量范围为10～800 ng/mL,灵敏度为0.2 ng/mL,批内、批间的变异系数(CV%)分别为3.4%～5.5%及5.0%～7.3%,与癌胚抗原、人白蛋白、人类心脏铁蛋白以及血红蛋白交叉反应率均小于1%。本法37℃、9 d热稳定性良好。表明所建立的方法各项指标均满足临床检测要求,抗体及样本用量少,操作简便,反应迅速,便于临床应用,可替代国外同类试剂盒。     

Standard Gibbs free energies of reactions of ozone with free radicals in aqueous solution: quantum-chemical calculations

Free radicals are common intermediates in the chemistry of ozone in aqueous solution. Their reactions with ozone have been probed by calculating the standard Gibbs free energies of such reactions using density functional theory (Jaguar 7.6 program). O(2) reacts fast and irreversibly only with simple carbon-centered radicals. In contrast, ozone also reacts irreversibly with conjugated carbon-centered radicals such as bisallylic (hydroxycylohexadienyl) radicals, with conjugated carbon/oxygen-centered radicals such as phenoxyl radicals, and even with nitrogen- oxygen-, sulfur-, and halogen-centered radicals. In these reactions, further ozone-reactive radicals are generated. Chain reactions may destroy ozone without giving rise to products other than O(2). This may be of importance when ozonation is used in pollution control, and reactions of free radicals with ozone have to be taken into account in modeling such processes.     

离子色谱法和紫外光度法测定大气降水中硝酸盐的比较研究

大气降水中硝酸盐的含量直接决定了空气污染程度,对硝酸盐含量进行测定对我国环保事业的开展有重要意义.我国常用离子色谱法和紫外光度法测定大气降水中硝酸盐的含量,本文尝试对离子色谱法和紫外光度法测定大气降水中硝酸盐的效果进行了对比研究.     

Ripening and spoilage of sugar salted herring with and without nitrate.

The technological effect of nitrate and the possible role of this compound in the formation of volatile nitrosamines during ripening and spoilage of sugar salted herring have been examined. In total, 600 barrels of fish with various amounts of nitrate added to the curing salt were prepared and stored under commercial conditions. During storage (18 months) the organoleptic, microbiological and chemical changes were studied. Additionally, a number of model experiments were carried out to evaluate the effect of nitrate on microbial growth and chemical changes. It was found that addition of nitrate significantly influences the colour of the fish while texture and flavour are not affected. Based on both the practical experiments and the model studies it is concluded that nitrate per se does not inhibit any microbial growth. Growth of strict anaerobes does not occur until the substrate is depleted of TMAO, and nitrate is effective in delaying the most common type of spoilage by delaying the TMAO reduction.
Small amounts of nitrosodimethylamine—up to 2.9 ppb has been detected—was formed in the sugar salted herring, but the addition of nitrate to the curing salt had no influence.