Development of a new automatic ozone concentration control system

An automatic ozone control recorder was developed in order to perform more reproducible ozone tests and to facilitate ease of operation. It is based on the principle of the iodometric method, and is in good agreement with the counter current method and the coulometric method. This development has been found to simplify the operational procedure and to improve the reproducibility of ozone tests.     

Development of passive sampler technique for ozone monitoring. Estimation of indoor and outdoor ozone concentration

A passive sampler method has been developed for ozone monitoring. The method involves a badge type passive sampler and is applied to the analysis of ozone exposure as an indoor and outdoor air pollutants. The passive sampler used in this experiment consists of glass fiber filter coated with NaNO(2), Na(2)CO(3) and ethylene glycol, and diffusion filter to remove the wind effects and several spacer effects. The principle component of coating is nitrite ion, which in the presence of ozone is oxidized to nitrate ion on the filter medium and then analyzed by ion chromatography. The results from laboratory and field tests show excellent correlation between the passive method and standard ozone monitoring system, integrated over the same time period. The wind tunnel parameters that were examined show that determination of relative humidity (ranging from 30 to 80%), temperature (ranging from 10 to 20 degrees C) and wind velocity ( ranging from 0.5 to 1.5 m s(-1)) at typical ozone levels (1-40 ppb) do not influence sampler performance. The detection limit attained 0.1 ppb is adequate for the determination of ozone in indoor and outdoor areas. A statistical comparison with a reference method was done in order to demonstrate the validation of the developed method. The accuracy of the proposed method, expressed as a percent relative error, when compared with a standard reference method, is found to be better than about +/-3.5%. The standard errors of the difference was measured in terms of relative standard deviation (R.S.D.) and it was found that the R.S.D. of the passive sampler for O(3) sampler ranged from 2.0 to 6.0%.     

臭氧发生器所产生气体中氮氧化物的HPLC法测定

基于氮氧化物溶于水生成HNO2和HNO3的反应,采用NaOH溶液收集氮氧化物,用高效液相色谱法测定氮氧化物,并用分光光度法作对比。结果表明,分光光度法所测结果偏低,高效液相色谱法更准确而且简便、快速,选择性好。     

Remote measurements of ozone concentration and aerosols in the Arctic stratosphere

Summary A LIDAR instrument for measurements of the ozone concentration and of aerosols in the middle atmosphere is briefly described. Data sets for ozone and aerosols, obtained at Spitsbergen during winter and early spring in 1989 and 1990, are presented. The Arctic ozone layer was found to be strongly influenced by atmospheric dynamics; a dramatic ozone depletion was not observed. Polar stratospheric clouds were detected in each winter, their dependence on the ambient atmospheric temperature is described.     

臭氧催化氧化脱除低浓度甲醛的新方法

甲醛作为一种典型的室内挥发性有机污染物,对人体健康危害很大.目前,在可用于室内甲醛脱除的诸多方法之中,臭氧催化氧化法因可于室温下使用廉价的金属氧化物催化剂实现对甲醛的高效脱除,从而受到了科研工作者的广泛关注.然而,考虑到室内甲醛的浓度极低,且存在着长期缓慢释放的特点,传统的臭氧催化氧化法应用于实际的室内甲醛脱除不仅会造成能量的浪费,而且还易因未完全分解臭氧的连续释放带来二次污染问题.为了提高臭氧催化氧化脱除甲醛过程的臭氧利用率,降低能耗,并有效缓解未分解臭氧引起的二次污染,本文将一种循环的甲醛存储-臭氧催化氧化新方法应用于室内低浓度甲醛的脱除.该新方法包含甲醛存储与臭氧催化氧化两个过程,在存储阶段低浓度甲醛吸附存储于催化剂表面,而在臭氧催化氧化阶段臭氧将存储的甲醛氧化为CO2与H2O,并重新释放催化剂表面的吸附位.因负载型氧化锰具有优良的臭氧分解能力,本研究以Al2O3负载的MnOx为催化剂,通过研究前驱体及担载量对甲醛脱除反应的影响,筛选出了最优的MnOx/Al2O3催化剂,并对相对湿度的影响规律进行了考察,最后通过低浓度甲醛存储-臭氧催化氧化循环实验验证了该甲醛臭氧催化氧化新过程的可靠性.我们采用传统的等体积浸渍法,基于不同的前驱体制备MnOx/Al2O3催化剂.XRD表征结果表明,乙酸锰为前驱体制得的MA/Al2O3催化剂中MnOx相主要为Mn3O4(粒径约为6.0 nm);而硝酸锰前驱体所得MN/Al2O3催化剂中则含有MnO2与Mn2O3相,且其MnOx颗粒粒径较大,约为9.5 nm.XPS测试结果表明,MA/Al2O3催化剂含有Mn2+,Mn3+及Mn4+,其中Mn3+与Mn4+的含量分别为75%与12%;而MN/Al2O3催化剂则仅含有Mn3+与Mn4+,含量分别为35%与65%.上述XRD与XPS结果相一致,说明以乙酸锰为前驱体所得催化剂的分散度较高且易形成低氧化态的Mn.甲醛存储-臭氧催化氧化实验结果表明,与Al2O3及MN/Al2O3相比,MA/Al2O3催化剂具有更高的甲醛存储与催化氧化脱除性能.基于MA/Al2O3催化剂,不同Mn负载量下的甲醛存储与臭氧催化氧化实验结果表明,Mn负载量为10 wt%时MA/Al2O3的性能最佳.因而,进一步的实验中我们均选用最优的10 wt%MA/Al2O3为催化剂,其在50%相对湿度下的甲醛存储量为26.9μmol/mL,臭氧催化氧化阶段碳平衡为92%,CO2选择性为100%.相对湿度的影响结果(23℃)则表明,由于水分子与甲醛分子间存在着竞争吸附作用,甲醛存储容量随相对湿度的增加而降低;但因相对湿度增加可建立利于甲醛氧化的新途径,故臭氧催化氧化性能随相对湿度增加而增强.综合考虑,10 wt%MA/Al2O3上甲醛存储-臭氧催化氧化的最优相对湿度为50%.为验证所提出新方法的实用性,我们基于10 wt%MA/Al2O3开展了甲醛存储-臭氧催化氧化的4次循环实验.4次循环实验中的甲醛存储以及臭氧催化氧化处理的规律可基本保持一致.50%相对湿度下,低浓度甲醛(15×10-6)在空速为27000 h-1时的穿透时间为110 min,而在臭氧催化氧化阶段(150×10-6臭氧,空速15000 h-1)仅需约50 min即可实现对存储甲醛的氧化脱除(碳平衡大于92%,CO2选择性100%),表明该新方法较传统的臭氧催化氧化方法臭氧用量可节省60%.     

Measurement of concentration gradients in swelling crosslinked polymer beads

The concentration of solvent in the gel phase of a swelling polystyrene–divinylbenzene copolymer bead has been measured as a function of the radius by optical interference techniques. It is found that an appreciable gradient exists even shortly after the core disappears. Results are presented for two cases: a very lightly crosslinked bead that exhibits negligible birefringence while swelling, and a more tightly crosslinked network in which the birefringence must be considered. It is also found that the refractive index of the unswollen bead is considerably less than that found by extrapolation from the swollen state; this effect is reasonable when the “free volume” in the bulk polymer is considered.     

Measurement of density and chemical concentration using a microfluidic chip

A new microfluidic product for measuring fluid density, specific gravity and chemical concentration has been developed. At the core of this lab-on-a-chip sensor is a vacuum-sealed resonating silicon microtube. Measurements can be made with under a microliter of sample fluid, which is over 1000x less than is conventionally required. Since the product is MEMS-based the overall system size is a fraction of conventional density meters and it weighs much less than the traditional desk-top, temperature controlled, density meters. The syringe or pipette loaded system includes a dynamic temperature control system that operates between 0 degree C and 90 degree C with an accuracy of less than 0.01 degree C. Density measurement accuracies of 4 to 5 digits have been observed with aqueous solutions. Measurement examples and applications will be discussed.     

Measurement of benzene concentration in urban air using passive sampling

The concentration of benzene in urban air in the Tri-City area of Poland (Gdańsk–Sopot–Gdynia, and Tczew) was assessed using diffusive passive samplers (Radiello). Samples were collected during a four-year monitoring campaign (2007–2010) at selected monitoring stations managed by the Agency of Regional Air Quality Monitoring in the Gdańsk Metropolitan Area (ARMAAG) Foundation. The performance of the passive samplers was investigated in a field study that measured the benzene concentration in urban air. The results obtained by the Radiello samplers were compared with the results obtained using an on-line monitor (Chrompack CP 7001). Statistical analysis of the results obtained by the two different techniques (passive and on-line) was performed by a linear regression method (Student’s t-test). The influence of temperature fluctuations on the uptake rate behavior of the passive samplers was also investigated.     

Measurement of uranium concentration in soil samples by two different methods

In the present work, uranium concentration was determined in 15 soil samples by using CR-39 nuclear track detector and NaI(Tl) gammaspectroscopy. Obtained data are compared.     

Ozone reduction at Nafion modified Au electrode and the measurement of ozone concentration in highly resistive solutions

The mass transport and charge transfer kinetics of ozone reduction at Nafion coated Au electrodes were studied in 0.5 mol/L H2SO4 and highly resistive solutions such as distilled water and tap water. The diffusion coefficient and partition coefficient of ozone in Nafion coating are 1.78×10-6 cm2·s-1 and 2.75 at 25℃ (based on dry state thickness), respectively. The heterogeneous rate constants and Tafel slopes for ozone reduction at bare Au are 4.1×10-6 cm·s-1, 1.0×10-6 cm·s-1 and 181 mV, 207 mV in 0.5 mol/L H2SO4 and distilled water respectively and the corresponding values for Nafion coated Au are 5.5×10-6 cm·s-1, 1.1×10-6 cm·s-1 and 182 mV, 168 mV respectively. The Au microelectrode with 3 μm Nafion coating shows good linearity over the range 0-10 mmol/L ozone in distilled water with sensitivity 61 μA·ppm-1 ·cm-2, detection limit 10 ppb and 95% response time below 5 s at 25℃. The temperature coefficient in range of 11-30℃ is 1.3%.     

Interaction between ozone and the chloride ion in sulfuric acid solutions up to 6-M concentration

The effect of sulfuric acid concentration on Cl₂ evolution in the reaction between O₃ and Cl^? has been investigated. The catalytic effects of metal ions in this reaction have been studied as a function of solution acidity. The chlorine evolution rate increases markedly with increasing acid concentration. At acid concentrations below 4 mol/l, the most effective catalyst is Co²⁺. The catalytic activities of Fe³⁺ and Cu²⁺ peak at $C_{H_2 SO_4 } $ = 4.8 mol/l. In passing to highly acidic solutions ( $C_{H_2 SO_4 } $ > 5 mol/l), the catalytic activity of the metal ions decreases, but the chlorine evolution rate remains high owing to the high acidity. Kinetics of VO²⁺ oxidation with ozone in acid media have been studied, and the ozone solubility in aqueous sulfuric acid has been measured.     

Measurement of radon concentration in groundwater in the Ashanti region of Ghana

Radon in groundwater and their annual effective dose in the Ashanti region of Ghana have been determined using the continuous grab sampling technique and an AB-5 detector. Mean levels of radon were in the range of 0.51–46.16 Bq L^?1. Effective annual doses ranged from 0.18–16.16, 0.13–12.08 and 0.09–8.31 μSv y^?1 for infants, children and adults, respectively. These values are significantly lower than the reference level of 0.1 mSv y^?1 recommended by the WHO and United Nations Scientific Committee on the Effects of Atomic Radiation for members of the public.     

On the action of ozone at high concentration on various grades of polyethylene and certain straight chain paraffins

The surface functionalisation of UHMWPE (ultra high molecular weight polyethylene) was successfully achieved by the action of ozone (10% by weight in oxygen) under mild conditions. The kinetics of the gas-solid reaction between O₃ and UHMWPE in powder form were measured in an IR gas cell and the pseudo-first-order rate constant was k′_UHMWPE = 1.9 × 10⁻⁴ s⁻¹. The resulting surface-oxidized UHMWPE was studied by FT-IR spectroscopy and the nature of the surface functionalities was determined. Furthermore, the surface-oxidized UHMWPE was studied by DSC (differential scanning calorimetry). It was evident that ozone attacks and oxidizes the amorphous phase of UHMWPE preserving the crystalline phase because after the ozone treatment there was an increase in the % of crystallinity. Two other polyethylene grades having respectively M_w = 15,000 Da (defined as LMWPE = low molecular weight polyethylene) and M_w = 4000 Da (defined as VLMWPE = very low molecular weight polyethylene) were studied as model compounds in comparison to UHMWPE in their reaction with ozone. Commercial liquid paraffin and n-dodecane were used as model compounds to study the reaction between high ozone concentration and alkanes.     

Measurement of dilute metallic impurity concentration in lead by differential scanning calorimetry

The traditional method for purity determination by analysis of the peak shape of the melting transition has included fitting to a linear relation between sample temperature (T) and the reciprocal fraction molten ($\text{1}\text{7}$). This technique, however, necessitates the use of a series of calibrants to determine the proper choice of limits for $\text{1}\text{7}$ as a function of purity. In this paper, a non-linear relation between T and $\text{1}\text{7}$ is developed and applied to the determination of metallic impurities in Pb in the range of a few to 1000 parts per million. The results are found to be independent of the range of $\text{1}\text{7}$ used. The use of differential scanning calorimety in this determination is discussed, and rate effects are also mentioned.     

A platinum-like behavior electrocatalyst and solid polymer electrolyte technique used on high concentration of electrochemical ozone water generation

This study presents an advanced ozone production process using the solid polymer electrolyte (SPE) technique, similar to the fabrication of proton exchange membrane fuel cell (PEMFC) membrane electrode assembly (MEA). Tungsten carbide and platinum on carbon black are coated on anode and cathode sides of a polymer membrane (Du Pont), respectively, to produce high concentration of ozone water. The water electrolysis of ozone generation requires a higher voltage than that of hydrogen production. On one hand, tungsten carbide, which is a platinum-like behavior electrocatalyst, plays a key role in preventing the MEA from corroding or oxidizing under high voltage. On the other hand, the carbon paper is replaced by a titanium porous disc to bear higher voltage. Moreover, an outstanding electronic control system can produce 1.37 ppm ozone water at atmosphere by adjusting the voltage range (6–10 V) with a current set to the maximum of 3 A for a household demand of ozone water generation.     

Measurement of non-methane hydrocarbons in Taipei city and their impact on ozone formation in relation to air quality

Air pollutants data from semi-continuous measurements at multiple sampling sites in Taipei metropolitan area of Taiwan was obtained by collecting air samples in canisters. The hydrocarbon composition was determined by using GC/MS and GC/FID. The air samples were pre-concentrated onto glass beads prior to separation by PLOT and DB-1 columns of GC. The method showed detection limit of <1 ppb and relative standard deviation in the range of 5-30% for different compounds. Aromatic hydrocarbons (toluene, benzene, etc.) and aliphatic hydrocarbons (ethylene, acetylene, propane, etc.) were correlated primarily to determine the source of emission. The estimated hydrocarbons were ranked according to their abundance and photochemical reactivity. The criteria pollutants, ozone and NO₂ were measured by UV-differential optical absorption spectroscopy (UV-DOAS), and were utilized to determine the relative importance of non-methane hydrocarbons (NMHC) and significant contribution of NO₂ in limiting ozone formation. The obtained results suggest that ozone formation in Taipei city is probably limited by the supply of non-methane hydrocarbons. The concentration profile of targeted pollutants was compared to other metropolitan areas to determine air quality and the pollutant sources.