Relative-rate study of the gas-phase reaction of hydroxy radicals with difunctional organic nitrates at 298 K and atmospheric pressure

Rate coefficients for the reactions of difunctional nitrates with atmospherically important OH radicals are not currently available in the literature. This study represents the first determination of rate coefficients for a number of C(3) and C(4) carbonyl nitrates and dinitrates with OH radicals in a 38 l glass reaction chamber at 1000 mbar total pressure of synthetic air by 298±2 K using a relative kinetic technique.The following rate coefficients (in units of 10^-12 cm³ molecule^-1 s^-1) were obtained: 1,2-propandiol dinitrate, <0.31; 1,2-butandiol dinitrate, 1.70±0.32; 2,3-butandiol dinitrate, 1.07±0.26; -nitrooxyacetone, <0.43; 1-nitrooxy-2-butanone, 0.91±0.16; 3-nitrooxy-2-butanone, 1.27±0.14; 1,4-dinitrooxy-2-butene, 15.10±1.45; 3,4-dinitrooxy-1-butene, 10.10±0.50.The possible importance of reaction of OH as an atmospheric sink for the compounds compared to other loss processes is considered.     

Natural Protection Against Groundwater Pollution by Nitrates in the Central Valley of Chile/Protection Naturelle Contre la Pollution des Eaux Souterraines par les Nitrates Dans la Vallée Centrale du Chili

Abstract

The Central Valley of Chile is a zone of intensive agricultural activity. Historically, in this zone, large amounts of fertilizers have been applied and low technological level irrigation methods have been used. Contrary to what might be expected, the existing aquifers in the Central Valley do not contain significant nitrate that could be associated with agricultural activity. This situation leads one to infer the existence of favourable conditions for the occurrence of natural attenuating processes such as denitrification. Favourable conditions may be related to the particular soil and climatic conditions, and/or the structure and dynamics of the existing aquifers.     

Determination of nitrate in seawater: Nitrate to nitrite reduction with copper-cadmium alloy

Determination of nitrate in seawater first requires its reduction to nitrite. Construction of a reductor column for use during continuous flow analysis at sea is described. Novel use is made of an alloy of cadmium and copper ($\text{50}\text{50}\text{w}\text{w}$) crushed to between 500 and 350 μm. Its performance is similar to that of the cadmium wire type of reductor but offers advantages of easier preparation and control of reductor volume.     

Structure-Reactivity Based Estimation of the Rate Constants for Hydroxyl Radical Reactions with Hydrocarbons

The reaction with the OH radical constitutes the singlemost important removal process for most organiccompounds found in the atmosphere. Efforts to measurethe OH radical rate constants of all troposphericconstituents remain incomplete due to the largevariety of primary emitted compounds and theirtropospheric degradation products.Based on the measured rate constants of 250molecules with the OH radical, a structure-activityrelationship (SAR) for OH reactions has beendeveloped. The molecules used in the dataset includemost classes of tropospheric compounds (includingalkanes, alkenes, and oxygenated hydrocarbons), withthe exception of aromatic and halogen-containingcompounds. Using a new parameterization of themolecular structure, the overall agreement betweenmeasured values and those estimated using the SARdeveloped in this study is usually very good, with10% of the molecules showing deviations larger than50%. In particular, the estimated rate constants ofethers and ketones are in better agreement withexperimental data than with previous SARs (Kwok andAtkinson, Atmos. Environ. 29, 1685–1695,1995). Rate constants of organic nitrates werenot well described by the SAR used in thisstudy. The basic assumption that the additive rateconstant for a chemical group is only influenced byneighbouring functional groups did not allow a goodparameterization for the rate constants of organicnitrates. The use of a second parameter to alter thereactivity of C-H bonds in -position to thefunctional group resulted in markedly better agreementbetween calculated and measured rate constants, butwas not extended due to the limited set of data. This indicates that strong electron withdrawing groups(e.g., nitrate groups) might influence the reactivityof C-H bonds that are not directly adjacent.     

光谱预处理方法对硝酸盐测量模型影响实验研究及软件设计

基于Savitzky-Golay(SG)卷积平滑、正态变量变换(SNV)、一阶导数法、附加散射校正(MSC)和小波去噪(WDS)等信号处理方法,对水中硝酸盐偏最小二乘(PLS)测量模型的影响进行实验研究,采用评估均方差(RMSEE)、预测标准差(RMSEP)、相关系数(R)、预测值与样本浓度值回归关系显著性F检验对预处理效果进行考察。实验结果表明,经SG卷积平滑预处理的PLS模型预测准确性优于其他处理方法。同时编写了该5种光谱预处理方法软件,实现了光谱数据采集与预处理、谱图绘制和光谱保存等功能。     

Hydrochemical and bacteriological features of the groundwater: southern border of the Rharb basin (Morocco) / Caractérisation hydrochimique et bactériologique des eaux souterraines: bordure méridionale du bassin du Rharb (Maroc)

Abstract

The western reservoirs represent the principal groundwater system in Morocco. Demographic, industrial and agricultural developments during the last decade have markedly altered groundwater quality. The Mamora coastal aquifer system is among the Atlantic systems which are most heavily threatened by pollution. Agricultural and industrial activities, and rapid urban growth contribute to the pollution of the groundwater. Contamination transport is facilitated by a high permeability of the aquifer formations. In order to assess the actual groundwater quality of the Mamora aquifer and to understand the influence of the factors generating the pollution, an extensive multidisciplinary research programme is in progress, with hydrochemistry and microbiology playing essential roles. The present paper concerns the spatial distribution of physico-chemical parameters in the groundwater, subjected to domestic, industrial and agricultural pollution. Fifty-seven samples were analysed for several parameters (Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^?, SO₄ ^2?, HCO₃ ^?, NO₃ ^?, pH, electrical conductivity and temperature). The microbiological analysis of 143 samples reveals the presence of four kinds of indicator bacteria in the groundwater resources: faecal Streptococci, faecal coliform, Escherichia coli and Clostridium. The physico-chemical results and bacteriological monitoring show that the nitrate and bacteria concentrations exceed the maximum admissible levels, notably around pumping stations in the sectors of Sidi Taibi, Sidi Ahmed Taleb and Aïn Sbaâ. Contamination is generated by uncontrolled anthropogenic activities and accentuated by the high intrinsic vulnerability of the aquifer system. Several parameters appeared to exceed admissibility standards. Measures are recommended to prevent groundwater pollution in the region.