Simulated Atmospheric Conditions Research Articles

The feasibility of TEA CO2 laser-induced plasma for spectrochemical analysis of geological samples in simulated Martian conditions

The present work studies the possibility of using pulsed Transversely Excited Atmospheric (TEA) carbon dioxide laser as an energy source for laser-induced breakdown spectroscopy (LIBS) analysis of rocks under simulated Martian atmospheric conditions. Irradiation of a basaltic rock sample with the laser intensity of 56MWcm−2, in carbon-dioxide gas at a pressure of 9mbar, created target plasma with favorable conditions for excitation of all elements usually found in geological samples. Detection limits of minor constituents (Ba, Cr, Cu, Mn, Ni, Sr, V, and Zr) were in the 3ppm–30ppm range depending on the element. The precision varied between 5% and 25% for concentration levels of 1% to 10ppm, respectively. Generally, the proposed relatively simple TEA CO2 laser-LIBS system provides good sensitivity for geological studies under reduced CO2 pressure.

Investigations on the corrosion of constructional steels in different aqueous and simulated atmospheric environments

The corrosion behavior of three constructional steels used in Senegal, S235, S275 and S355, was studied in simulated atmospheric conditions in an exposure chamber above distilled water and above 3% NaCl solution representing marine atmosphere by comparing the ratio of rusted to unrusted area. Electrochemical test methods (potentiodynamic tests and electrochemical impedance spectroscopy) were employed to study the steels fully immersed in acidic, near neutral and basic conditions in 0.5 M HCl, NaCl, and NaOH solutions, respectively. Results indicate that S355 and S235 steels have comparable corrosion resistance, which are much lower than that of S275. KEY WORDS: Corrosion, Steel, Salt spray, Tafel polarization, Electrochemical impedance spectroscopy Bull. Chem. Soc. Ethiop. 2015, 29(2), 299-310DOI: http://dx.doi.org/10.4314/bcse.v29i2.12

Simulating Flow and Dispersion by Using WRF-CFD Coupled Model in a Built-Up Area of Shenyang, China

Results are presented from a series of numerical studies designed to investigate the atmospheric boundary layer structure, ambient wind, and pollutant source location and their impacts on the wind field and pollutant distribution within the built-up areas of Shenyang, China. Two models, namely, Open Source Field Operation and Manipulation (OpenFOAM) software package and Weather Research and Forecasting (WRF) model, are used in the present study. Then the high resolution computational fluid dynamics (CFD) numerical experiments were performed under the typical simulated atmospheric boundary conditions. It was found that the atmospheric boundary structure played a crucial role in the pollution within the building cluster, which determined the potential turbulent diffusion ability of the atmospheric surface layer; the change of the ambient wind direction can significantly affect the dispersion pattern of pollutants, which was a more sensitive factor than the ambient wind speed; under a given atmospheric state, the location of the pollution sources would dramatically determine the pollution patterns within built-up areas. The WRF-CFD numerical evaluation is a reliable method to understand the complicated flow and dispersion within built-up areas.

A Smog Chamber Facility for Qualitative and Quantitative Study on Atmospheric Chemistry and Secondary Organic Aerosol

In order to investigate the atmospheric oxidation processes and the formation of secondary organic aerosol (SOA), an indoor environmental reaction smog chamber are constructed and characterized. The system consists of the collapsible ∼830 L FEP Teflon film main reactor, in which the atmospheric chemical reactions take place and the formation of SOA occurs under the simulated atmospheric conditions, and the diverse on-line gas- and particle-phase instrumentation, such as the proton transfer reaction mass spectrometer, the synchrotron radiation photoionization mass spectrometer, the aerosol laser time-of-flight mass spectrometer, and other traditional commercial instruments. The initial characterization experiments are described, concerning the temperature and ultraviolet light intensity, the reactivity of the pure air, the wall loss rates of gaseous compounds and particulate matter. And the initial evaluation experiments for SOA yields from the ozonolysis of α-pinene and for mass spectra of the products resulting from the photooxidation of OH initiated isoprene are also presented, which indicate the applicability of this facility on the studies of gas-phase chemical mechanisms as well as the formation of SOA expected in the atmosphere.

SO2 sorption by activated carbon supported ionic liquids under simulated atmospheric conditions

This work evaluates the ability of ionic liquid loaded activated carbon sorbents to remove SO2 under simulated atmospheric conditions of 15ppm SO2 in air, temperature of 25°C and relative humidity of 50%. Amongst the nine ionic liquid (1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium lactate, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-allyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium methyl sulfate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hydrogen sulfate, 1-hexyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate and 1-butyl-3-methylimidazolium hydrogensulfate) sorbents studied, the 1-ethyl-3-methylimidazolium acetate loaded activated carbon exhibited the highest SO2 sorption capacity performance. The attained results clearly indicate that some ionic liquids such as 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with high absorptivity in pure SO2 would perform poorly under practical conditions. As a result of the superior performance of the 1-ethyl-3-methylimidazolium acetate loaded activated carbon, further tests and characterizations were performed on the sorbent. The performance of 1-ethyl-3-methylimidazolium acetate sorbent increased along with ionic liquid loading onto the activated carbon. The 1-ethyl-3-methylimidazolium acetate sorbent breakthrough time was greater than pure activated carbon and 10wt% potassium hydroxide loaded activated carbon standard. The SO2 sorption rate of 1-ethyl-3-methylimidazolium acetate loaded activated carbon was inversely proportional to test bed temperature. FTIR–ATR, NMR and thermal analysis of SO2 sorbed 1-ethyl-3-methylimidazolium acetate loaded activated carbon indicated the presence of both physisorbed and chemisorbed SO2.

Photodegradation of pyrene on Al2O3 surfaces: a detailed kinetic and product study.

In the current study, the photochemistry of pyrene on solid Al2O3 surface was studied under simulated atmospheric conditions (pressure, 1 atm; temperature, 293 K; photon flux, JNO2 = 0.002-0.012 s(-1)). Experiments were performed using synthetic air or N2 as bath gas to evaluate the impact of O2 to the reaction system. The rate of pyrene photodegradation followed first order kinetics and was enhanced in the presence of O2, kd(synthetic air) = 7.8 ± 0.78 × 10(-2) h(-1) and kd(N2) = 1.2 ± 0.12 × 10(-2) h(-1) respectively, due to the formation of the highly reactive O2(•-) and HO(•) radical species. In addition, kd was found to increase linearly with photon flux. A detailed product study was realized and for the first time the gas/solid phase products of pyrene oxidation were identified using off-line GC-MS and HPLC analysis. In the gas phase, acetone, benzene, and various benzene-ring compounds were determined. In the solid phase, more than 20 photoproducts were identified and their kinetics was followed. Simulation of the concentration profiles of 1- and 2-hydroxypyrene provided an estimation of their yields, 33% and 5.8%, respectively, with respect to consumed pyrene, and their degradation rates were extracted. Finally, the mechanism of heterogeneous photodegradation of pyrene is discussed.

Heterogeneous reactions of particulate matter-bound PAHs and NPAHs with NO3/N2O5, OH radicals, and O3 under simulated long-range atmospheric transport conditions: reactivity and mutagenicity.

The heterogeneous reactions of ambient particulate matter (PM)-bound polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs (NPAHs) with NO3/N2O5, OH radicals, and O3 were studied in a laboratory photochemical chamber. Ambient PM2.5 and PM10 samples were collected from Beijing, China, and Riverside, California, and exposed under simulated atmospheric long-range transport conditions for O3 and OH and NO3 radicals. Changes in the masses of 23 PAHs and 20 NPAHs, as well as the direct and indirect-acting mutagenicity of the PM (determined using the Salmonella mutagenicity assay with TA98 strain), were measured prior to and after exposure to NO3/N2O5, OH radicals, and O3. In general, O3 exposure resulted in the highest relative degradation of PM-bound PAHs with more than four rings (benzo[a]pyrene was degraded equally well by O3 and NO3/N2O5). However, NPAHs were most effectively formed during the Beijing PM exposure to NO3/N2O5. In ambient air, 2-nitrofluoranthene (2-NF) is formed from the gas-phase NO3 radical- and OH radical-initiated reactions of fluoranthene, and 2-nitropyrene (2-NP) is formed from the gas-phase OH radical-initiated reaction of pyrene. There was no formation of 2-NF or 2-NP in any of the heterogeneous exposures, suggesting that gas-phase formation of NPAHs did not play an important role during chamber exposures. Exposure of Beijing PM to NO3/N2O5 resulted in an increase in direct-acting mutagenic activity which was associated with the formation of mutagenic NPAHs. No NPAH formation was observed in any of the exposures of the Riverside PM. This was likely due to the accumulation of atmospheric degradation products from gas-phase reactions of volatile species onto the surface of PM collected in Riverside prior to exposure in the chamber, thus decreasing the availability of PAHs for reaction.

Evaluation of an Imidazoline in Simulated Atmospheric Conditions as Corrosion Inhibitor through Electrochemical Noise

This work presents electrochemical noise measurement results from assessment of 2-methyl-2-imidazoline as inhibitor on a 1018 steel, at different relative humidity, categorized according to ASTM E 104 85.A modified steel plates atmospheric corrosion probe (MECA) was used in order to measure potential and current noise time series; by using MECA, atmospheric corrosion rate could be determined, even if humidity was low.Imidazoline is widely used in petrochemical industry as a corrosion inhibitor, so that was the reason for studying the behavior of this inhibitor in other corrosive processes as in the packaging or protection of metals exposed to atmosphere.Spectral and statistical analysis of the noise data was carried out; after that, polarization curves were conducted to validate the information from noise and the use of MECA monitor. From the results, it was established that 2-methyl-2 imidazoline decreasing anodic potential and modifies the double layer adsorption. The use of MECA monitor was validated, founding that records were reliable for electrochemical measurements of atmospheric corrosion.

A laboratory study of the oxidation of non toxic Cr(III) to toxic Cr(VI) by OH• free radicals in simulated atmospheric water droplets conditions: Potential environmental impact

In atmospheric waters, oxidation of Cr(III) to Cr(VI) by OH• free radicals is a major environmental hazard since non-toxic species is transformed into toxic one. It is important to obtain some details concerning this oxidation reaction. In this study we simulated this oxidation by steady state radiolysis using 60Co radioactive source and pulse radiolysis technique using a 2.5MeV van de Graaff electron accelerator and investigated its kinetics in the pH range 1 to 9. Our findings showed that the reaction was highly pH dependant with a maximum yield at pH 4. The electron transfer proceeds via an inner sphere mechanism with (i) formation of the [OH•–Cr(III)] adduct with an equilibrium constant of 2.34×104mol−1dm−3 then (ii) followed by an electron transfer from Cr(III) to OH• within the adduct with a rate constant of 2.51×104s−1. The implication of this oxidation to atmospheric chromium contamination is discussed.

Correction of Atmospheric Phase Screen in Time Series InSAR Using WRF Model for Monitoring Volcanic Activities

One of the main limitations in measuring ground deformation using synthetic aperture radar interferometry (InSAR) is atmospheric phase delay effects. In volcanic regions, the atmospheric phase delay effects can cause serious problems in detecting volcanic unrest because atmospheric thickness is inversely related with the elevation of a volcanic mountain. It is commonly known that the atmospheric phase screen (APS) can be decomposed spatially into stratified and turbulent components. In this paper, the stratified and turbulent atmospheric conditions of a volcanic area were simulated using weather research and forecasting (WRF) model, and the simulated atmospheric conditions were compared with in situ radiosonde data. The comparison results proved that the stratified APS from the WRF model could reflect the reasonable patterns of seasonal changes and vertical profiles with dependable quality. We also found that the stratified APS was significantly correlated with time and sometimes severely contaminated the quality of volcanic deformation estimation. These results indicate that the temporal high-pass (HP) filtering, which has been usually applied in time series InSAR analysis for extracting and removing APS, cannot work properly in volcanic area. Thus, we propose a new method that employs the stratified APS obtained from the WRF model by correlating with topography and the (residual) turbulent APS that can be effectively eliminated by temporal HP filtering in persistent scatterer interferometry (PSI). We applied the proposed method (atmosphere-corrected PSI) to Advanced Land Observing Satellite Phased Array type L-band SAR data that cover Shinmoedake volcano, Japan, and found that the estimated surface deformation and APS agreed well with those measured from GPS and Moderate-Resolution Imaging Spectroradiometer data, respectively.

Marine Aerosol Drop Size Effects on the Corrosion Behavior of Plain Carbon Steel

In this research, a novel methodology was developed to study corrosion under aqueous electrolyte drops ranging in diameter from 20-1000 mm, the most common drop sizes found in coastal marine environments. The objective of this work was to examine the relationship between drop size and corrosion attack of bare low carbon steel under simulated atmospheric marine conditions. A drop-on-demand inkjet printer was custom built by coupling a commercial jetting device with a programmable two-axis stage. Singular droplets of sodium chloride (6.2 M NaCl in H2O and 8.7 mM in ethanol) were deposited on polished 1010 steel coupons and then exposed to a 75% relative humidity environment for 24 hours. It was found that, in general, the volume loss increased with drop diameter according to a power law. Corrosion always occurred under drops greater than 150 μm in diameter, but was not consistently observed under drops in the 20-100 mm range. The fraction of drops that showed no corrosion increased with decreasing drop size below 100 μm. However, drops smaller than 100 μm that caused corrosion were found to have the greatest volume loss compared to their salt loading density. Therefore, the manner and geometry in which salt is deposited onto a low carbon steel surface, along with the mode of attack, will significantly affect corrosion loss. From a technical standpoint, these results suggest that service life prediction approaches, including accelerated testing, will more accurately simulate natural atmospheres if electrolyte geometry is taken into account for these materials.

Relative rate coefficient measurements of OH radical reactions with (Z)-2-hexen-1-ol and (E)-3-hexen-1-ol under simulated atmospheric conditions

The relative rate technique was used to determine the rate coefficients of the reactions of OH radicals with (Z)-2-hexen-1-ol (k1), and (E)-3-hexen-1-ol (k2), at (296 ± 2) K and (750 ± 10) Torr of N2 or pure air. The reactions were investigated using a 200 L Teflon reaction chamber and a gas chromatograph coupled with flame-ionization detection. The following rate coefficients were derived, in units of cm3 mol−1 s−1: k1 = (1.1 ± 0.4) × 10−10 and k2 = (0.8 ± 0.1) × 10−10. This is the first experimental determination of k1 and k2. A comparison between the experimental rate coefficients (kexp) and the calculated rate coefficients using the structure–activity relationship (SAR) method (kSAR), for the reaction of different unsaturated alcohols with OH radicals is presented. The atmospheric lifetimes of the studied alcohols were estimated considering the rate coefficients of their reactions with OH and NO3 radicals. The radiative efficiencies (REs) were obtained from the infrared spectra of the two hexenols and the global warming potentials (GWPs) were then estimated. Atmospheric implications of the alcohols emission are briefly discussed.

The ice repellency of plasma polymerized hexamethyldisiloxane coating

A superhydrophobic thin film was deposited on an aluminium oxide substrate by low pressure plasma polymerization of hexamethyldisiloxane (HMDSO). The coating was determined to be superhydrophobic due to its high water contact angle (∼158°) and low contact angle hysteresis. The aim of this work is to verify the icephobic properties of the HMDSO thin films obtained under simulated atmospheric conditions in a wind tunnel at sub-zero temperature and subsequent centrifugal adhesion test. The results obtained showed that the ice adhesion strength of the superhydrophobic HMDSO coating was 3.5 times lower than that on an aluminium substrate as reference tests. Although ice adhesion strength of the surface increased after 15 times icing/de-icing cycles, the surface kept its icephobic properties (ice adhesion strength 1.4 times lower than untreated aluminium).

Heterogeneous Oxidation of Terbuthylazine by “Dark” OH Radicals under Simulated Atmospheric Conditions in a Flow Tube

In order to investigate the heterogeneous oxidation kinetics of the herbicide terbuthylazine (TERB), a stable and reproducible generation system of "dark" hydroxyl radical in the gas phase was developed and optimized using a PTR-MS. TERB was adsorbed on silica particles, which were coated on the walls of a flow tube. The hydroxyl radical was produced in the dark through the ozonolysis of 2,3-dimethyl-2-butene (DMB). The radical concentration was determined applying two different methods of calculation based on the monitoring of (i) a gaseous compound used as a tracer, m-xylene; (ii) one of the OH radical precursors, DMB. The obtained gaseous OH radical concentration in the reactor was (9.0 ± 4.0) × 10(7) radical cm(-3). Exposing TERB to the oxidant for 1-14 h, a heterogeneous kinetic constant of kOH = (1.5 ± 0.8) × 10(-13) cm(3) molecule(-1) s(-1) was found at 26 °C and RH < 1%. As a result, the heterogeneous oxidation of TERB by OH radicals seems to be much slower (by a factor of 63) when the organic compound is present in the particulate phase than when it reacts in homogeneous gas phase.

Sub-3 nm Particles Detection in a Large Photoreactor Background: Possible Implications for New Particles Formation Studies in a Smog Chamber

New particles formation experiments have been conducted in the experimental multiphasic atmospheric simulation chamber (CESAM) smog chamber. The nucleation events generated during the dark ozonolysis of sabinene were monitored using a neutral cluster and air ions spectrometer in the size range 0.8–42 nm under simulated atmospheric conditions. The measurements show that a significant amount of pre-existing clusters exist in the 1–2 nm size range even in very clean controlled conditions. Numerical modeling experiments indicate that a range of 9–67% of pre-existing clusters can explain, through activation by organic vapors, the number of new particles formed when sabinene is oxidized, with an increasing contributing fraction for increasing condensable vapor concentrations. These findings suggest that atmospheric simulation chambers backgrounds have to be carefully characterized for their sub-3-nm neutral cluster concentration content before nucleation parameterizations can be derived. Copyright 2013 American Association for Aerosol Research

Protective Role of Spore Structural Components in Determining Bacillus subtilis Spore Resistance to Simulated Mars Surface Conditions

Spores of wild-type and mutant Bacillus subtilis strains lacking various structural components were exposed to simulated Martian atmospheric and UV irradiation conditions. Spore survival and mutagenesis were strongly dependent on the functionality of all of the structural components, with small acid-soluble spore proteins, coat layers, and dipicolinic acid as key protectants.

Self passivating behavior of multilayer SiC under simulated atmospheric re-entry conditions

In view of possible application of multilayer SiC as oxidation resistant and self-passivating component of re-usable thermal protection systems for space re-entry vehicles, this material was tested in a re-entry simulation chamber. A multilayer SiC laminate was processed by tape casting and pressure less sintering. Both the as-processed multilayer SiC and a similar passivated material, with a surface silica layer obtained by high temperature oxidation, were investigated. The microstructure and the mechanical features of these two materials were compared before and after the re-entry test. Microstructure was investigated by XRD, SEM-EDS, XPS and density measurements. Flexural strength, Young modulus and hardness were measured as well. Oxidation, occurring during re-entry test or resulting from the pre-test oxidation treatment, only affected the external part of the multilayer, while the material core was practically unchanged after oxidation. Every kind of specimen retained almost completely the original mechanical features after 100 re-entry simulations.

Images reveal that atmospheric particles can undergo liquid–liquid phase separations

A large fraction of submicron atmospheric aerosol particles contains both organic material and inorganic salts. As the relative humidity cycles in the atmosphere and the water content of the particles correspondingly changes, these mixed particles can undergo a range of phase transitions, possibly including liquid-liquid phase separation. If liquid-liquid phase separation occurs, the gas-particle partitioning of atmospheric semivolatile organic compounds, the scattering and absorption of solar radiation, and the reactive uptake of gas species on atmospheric particles may be affected, with important implications for climate predictions. The actual occurrence of liquid-liquid phase separation within individual atmospheric particles has been considered uncertain, in large part because of the absence of observations for real-world samples. Here, using optical and fluorescence microscopy, we present images that show the coexistence of two noncrystalline phases for real-world samples collected on multiple days in Atlanta, GA as well as for laboratory-generated samples under simulated atmospheric conditions. These results reveal that atmospheric particles can undergo liquid-liquid phase separations. To explore the implications of these findings, we carried out simulations of the Atlanta urban environment and found that liquid-liquid phase separation can result in increased concentrations of gas-phase NO(3) and N(2)O(5) due to decreased particle uptake of N(2)O(5).

Development of a parallel sampling and analysis method for the elucidation of gas/particle partitioning of oxygenated semi-volatile organics: a limonene ozonolysis study

Abstract. The gas/particle partitioning behaviour of the semi-volatile fraction of secondary organic matter and the associated multiphase chemistry are key features to accurately evaluate climate and health impacts of secondary organic aerosol (SOA). However, today, the partitioning of oxygenated secondary species is rarely assessed in experimental SOA studies and SOA modelling is still largely based on estimated partitioning data. This paper describes a new analytical approach, solvent-free and easy to use, to explore the chemical composition of the secondary organic matter at a molecular scale in both gas and particulate phases. The method is based on thermal desorption (TD) of gas and particulate samples, coupled with gas chromatography (GC) and mass spectrometry (MS), with derivatisation on sampling supports. Gaseous compounds were trapped on Tenax TA adsorbent tubes pre-coated with pentafluorobenzylhydroxylamine (PFBHA) or N-Methyl-N-(t-butyldimethylsilyl)trifluoroacetamide (MTBSTFA). Particulate samples were collected onto quartz or Teflon-quartz filters and subsequently subjected to derivatisation with PFBHA or MTBSTFA before TD-GC/MS analysis. Method development and validation are presented for an atmospherically relevant range of organic acids and carbonyl and hydroxyl compounds. Application of the method to a limonene ozonolysis experiment conducted in the EUPHORE simulation chamber under simulated atmospheric conditions of low concentrations of limonene precursor and relative humidity, provides an overview of the method capabilities. Twenty-five compounds were positively or tentatively identified, nine being in both gaseous and particulate phases; and twelve, among them tricarboxylic acids, hydroxyl dicarboxylic acids and oxodicarboxylic acids, being detected for the first time.

A High-Resolution Simulation of the Year 2003 for Germany Using the Regional Model COSMO

AbstractIn this article, the authors examine the effect of a high-resolution grid (grid resolution lower than 3 km) in the context of a realistic climate simulation. For this purpose global simulation results of the German Weather Service were dynamically downscaled in a one-way nesting approach to 2.8 km using the regional forecast model of the Consortium for Small-Scale Modeling (COSMO) of the German Weather Service. The simulations were performed for the region of central Europe in 2003. In particular, the authors investigate whether COSMO adequately handles extreme events such as the persistent drought and heat of the summer of 2003. Comparisons of the simulated atmospheric conditions in terms of 2-m temperature, mean sea level pressure, and precipitation demonstrated a good correspondence to their associated observational data. Simulation results and observed data are both given as time series at locations such as grid cells or station locations. By cluster analysis a representation of the spatial structure for observation data and simulation results is found. The kappa statistic evaluates how well the two spatial structures correspond to each other. The different kappa variants are helpful to diagnose where shortcomings of the simulation results are located.