Tropospheric HO2 determination by FAGE

The detection efficiency is greatest at low pressures, where the subsequent removal of the HO product by the NO reagent (via HO + NO + M yields HONO + M) is relatively slow. Moreover, nozzle expansion of the air from ambient to low pressures produces a turbulent zone that assists in mixing the reagent with the sample. If the HO product is observed by laser-excited fluorescence, then the other advantages of low-pressure detection by FAGE (Fluorescence Assay with Gas Expansion) also apply. The FAGE instrumental response was calibrated to external HO2 by observing NO decay in the photolysis of HO-CH2O mixtures and by choosing conditions in which HO2 + NO is the only significant NO destruction path. HO2 was determined in urban air

Pressure dependence of ozone interference in the laser fluorescence measurement of OH in the atmosphere [comment]

The authors comment on the paper by Shirinzadeh et al. (Applied Optics, vol. 26, p. 2102, 1987). They point out three errors which caused the overprediction of spurious HO data

Effects of Different Types of Clays and Maleic Anhydride Modified Polystyrene on Polystyrene/Clay Nanocomposites

Polymer/clay nanocomposites are considered as a new subject of research in Iran and the world. Addition of a minimum amount of clay (2-5wt%) can improve the mechanical properties, enhance barrier properties and reduce flammability dramatically. Polystyrene (PS) exhibits high strength, high modulus and excellent dimensional stability, but it has poor ductility, elongation, and flexural modulus. By incorporating clay into polystyrene these properties can be improved. In this study preparation of polystyrene/clay nanocomposite, effects of different types of clays (Cloisite 10A andNanomer I.30TC) and maleic anhydride modified polystyrene on mechanical properties of the prepared polystyrene/clay nanocomposites were evaluated. Samples were prepared by a twin screw extruder. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques were employed to evaluate the extent of intercalation and exfoliation of silicate layers in the nanocomposites. Mechanical tests show that by addition of clay and maleic anhydride modified polystyrene the flexural modulus (~30%) and elongation-at-break (~40%) of prepared nanocomposites have been improved. XRD and TEM results show that nanocomposite have an intercalated structure with ability to change to further exfoliation structure

Generalized response of chemiluminescence analyzers

The mass flow and chemical kinetic equations for a gaseous chemiluminescence (CL) analyzer are formulated and solved. The resultant equation can be used to predict the absolute response of the analyzer as a function of the sample flow rate, the sample gas pressure, the chamber pressure, the chamber volume, the mass flow rate and mole fraction of the reagent gas, and the rate constants of the relevant chemical processes. Thus, the equation allows optimization of these parameters. It is shown that for varying sample pressure the analyzer can be used to measure either concentration or mole fraction and that interfering reactions can sometimes be discriminated against by chamber pressure variation. The equations apply equally well to a flowing-liquid-phase CL analyzer, if the chemical mechanism considered is appropriate

FAGE Measurements of Tropospheric HO with Measurements and Model of Interferences

Ambient HO measurements by low-pressure laser-excited fluorescence with chemical modulation, and supporting ozone and water-vapor data, are presented for periods in May and August 1987. The observed peak daytime ambient HO concentrations in Oregon are in the range (2.5 to 8) times106 molecules cm⁻³ and show small negative offsets due to photochemical interference. Direct measurements of the interference at fixed [O₃] give the dependence on ambient [H₂O] and on the modulating reagent [isobutane]. At ambient [O₃]=30 p.p.b. and 10 torr H₂O, with excitation and detection at a total pressure of 4 torr, the net interference is equal to [HO]=-1.3times10⁶ molecule cm⁻³

Diurnal HO₂ cycles at clean air and urban sites in the troposphere

HO₂ concentrations have been determined at two Oregon sites for continuous periods of 36 to 48 hours, using fluorescence assay with gas expansion. At the sea level coastal site (45degN 124degW), NNW winds prevailed during daytime, and a point measurement of very low total nonmethane hydrocarbon concentration indicated the presence of remote tropospheric air of oceanic origin. At the urban site, HO₂ was determined during moderately low ozone pollution levels. At both sites, maximum daily [HO₂] was in the range of 1-2times10⁸ cm⁻³ under clear-sky conditions, with an estimated overall uncertainty of 40%

Third-generation FAGE instrument for tropospheric hydroxyl radical measurement

The authors have constructed a single-stage, frequency-doubled, copper vapor laser-pumped dye laser to be used in the measurement of atmospheric hydroxyl radical concentrations. This laser can be tuned to either the 1← 0 or 0← 0 vibrational transition in the electronic transition ²Sigmalarr²Pi. A new photon counting instrument is used for HO fluorescence detection. Theoretical and experimental studies of instrument performance show better sensitivities and reduced photolytic interferences than have been possible with previous systems based upon Nd:YAG pumping

AGTR1 rs5186 variants in patients with type 2 diabetes mellitus and nephropathy

Diabetic nephropathy (DN) is one of the leading causes of death in patients with type 2 diabetes mellitus (DM) and genetic factor can influence development of this complication. Association of Angiotensin II receptor type 1 (AGTR1) gene and DN has been evaluated in recent years. This study aim was to assess the association of AGTR1 gene polymorphisms with DN in a group of Iranian diabetic patients. In the present study, 97 patients with DM, 94 patients with DN and 100 healthy controls were included. Allele and genotype frequencies of AGTR1A1166C (rs5186) were determined by ARMS PCR technique. In all groups, blood glucose concentration, creatinine, urea and HbA1c were measured and urine albumin to creatinine ratio (ACR) as well as glomerular filtration rate (GFR) was calculated. A statistically significant association was found between C allele of rs5186 and DN (odds ratio (OR) = 1.84 95% CI: 1.10�3.08; p_value = 0.03). Among patients with DM, carriers of C allele (AC + CC) had significantly higher ACR (p_value = 0.04) compared to AA homozygote patients. This study showed the association of AGTR1 gene polymorphisms (rs5186) with increased urinary albumin excretion in a group of Iranian patients with DM. Also, C allele can be introduced as a risk allele for DN. © 201