scholarly journals Actinometric measurements of NO<sub>2</sub> photolysis frequencies in the atmosphere simulation chamber SAPHIR

2004 ◽  
Vol 4 (6) ◽  
pp. 8141-8170
Author(s):  
B. Bohn ◽  
F. Rohrer ◽  
T. Brauers ◽  
A. Wahner
Keyword(s):  
Calibration Factor ◽  
Absolute Calibration ◽  
Chamber Volume ◽  
Photolysis Frequencies ◽  
Model Predictions ◽  
External Conditions ◽  
Atmosphere Simulation Chamber ◽  
Simulation Chamber ◽  
Model Approach

Abstract. The simulation chamber SAPHIR at Forschungszentrum Jülich has UV permeable teflon walls facilitating atmospheric photochemistry studies under the influence of natural sunlight. Because the internal radiation field is strongly affected by construction elements, we use external, radiometric measurements of spectral actinic flux and a model to calculate mean photolysis frequencies for the chamber volume (Bohn and Zilken, 2004). In this work we determine NO2 photolysis frequencies j(NO2) within SAPHIR using chemical actinometry by injecting NO2 and observing the chemical composition during illumination under various external conditions. In addition to a photo-stationary approach, a time-dependent method was developed to analyse the data. These measurements had two purposes. Firstly, to check the model predictions with respect to diurnal and seasonal variations in the presence of direct sunlight and secondly to obtain an absolute calibration factor for the combined radiometry-model approach. We obtain a linear correlation between calculated and actinometric j(NO2). A calibration factor of 1.34±0.10 is determined, independent of conditions in good approximation. This factor is in line with expectations and can be rationalised by internal reflections within the chamber. Taking into account the uncertainty of the actinometric j(NO2), an accuracy of 13% is estimated for the determination of j(NO2) in SAPHIR. In separate dark experiments a rate constant of (1.93±0.12)×10−14 cm3 s−1 was determined for the NO+O3 reaction at 298 K using analytical and numerical methods of data analysis.

scholarly journals Actinometric measurements of NO<sub>2</sub> photolysis frequencies in the atmosphere simulation chamber SAPHIR

2005 ◽  
Vol 5 (2) ◽  
pp. 493-503 ◽  
Author(s):  
B. Bohn ◽  
F. Rohrer ◽  
T. Brauers ◽  
A. Wahner
Keyword(s):  
Calibration Factor ◽  
Absolute Calibration ◽  
Chamber Volume ◽  
Photolysis Frequencies ◽  
Model Predictions ◽  
External Conditions ◽  
Atmosphere Simulation Chamber ◽  
Simulation Chamber ◽  
Model Approach

Abstract. The simulation chamber SAPHIR at Forschungszentrum Jülich has UV permeable teflon walls facilitating atmospheric photochemistry studies under the influence of natural sunlight. Because the internal radiation field is strongly affected by construction elements, we use external, radiometric measurements of spectral actinic flux and a model to calculate mean photolysis frequencies for the chamber volume Bohn04B. In this work we determine NO2 photolysis frequencies j(NO2) within SAPHIR using chemical actinometry by injecting NO2 and observing the chemical composition during illumination under various external conditions. In addition to a photo-stationary approach, a time-dependent method was developed to analyse the data. These measurements had two purposes. Firstly, to check the model predictions with respect to diurnal and seasonal variations in the presence of direct sunlight and secondly to obtain an absolute calibration factor for the combined radiometry-model approach. We obtain a linear correlation between calculated and actinometric j(NO2). A calibration factor of 1.34±0.10 is determined, independent of conditions in good approximation. This factor is in line with expectations and can be rationalised by internal reflections within the chamber. Taking into account the uncertainty of the actinometric j(NO2), an accuracy of 13% is estimated for the determination of j(NO2) in SAPHIR. In separate dark experiments a rate constant of (1.93±0.12)x10-14 cm3 s-1 was determined for the NO+O3 reaction at 298K using analytical and numerical methods of data analysis.

scholarly journals Model-aided radiometric determination of photolysis frequencies in a sunlit atmosphere simulation chamber

2005 ◽  
Vol 5 (1) ◽  
pp. 191-206 ◽  
Author(s):  
B. Bohn ◽  
H. Zilken
Keyword(s):  
Time Dependent ◽  
Clear Sky ◽  
Photolysis Frequencies ◽  
Model Predictions ◽  
Complex Construction ◽  
Sky Conditions ◽  
Atmosphere Simulation Chamber ◽  
Radiometric Determination ◽  
Simulation Chamber

Abstract. In this work diurnal and seasonal variations of mean photolysis frequencies for the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich are calculated. SAPHIR has a complex construction with UV permeable teflon walls allowing natural sunlight to enter the reactor volume. The calculations are based on external measurements of solar spectral actinic flux and a model considering the time-dependent impact of shadows from construction elements as well as the influence of the teflon walls. Overcast and clear-sky conditions are treated in a consistent way and different assumptions concerning diffuse sky radiance distributions are tested. Radiometric measurements inside the chamber are used for an inspection of model predictions. Under overcast conditions we obtain fractions of 0.74 and 0.67 of external values for photolysis frequencies j(NO2) (NO2+hν→NO+O(3P)) and j(O1D) (O3+hν→O2+O(1D)), respectively. On a clear sky summer day these values are time-dependent within ranges 0.65-0.86 and 0.60-0.73, for j(NO2) and j(O1D), respectively. A succeeding paper (Bohn et al., 2004) is dealing with an on-road test of the model approach by comparison with photolysis frequencies from chemical actinometry experiments within SAPHIR.

scholarly journals Model-aided radiometric determination of photolysis frequencies in a sunlit atmosphere simulation chamber

2004 ◽  
Vol 4 (5) ◽  
pp. 6967-7010
Author(s):  
B. Bohn ◽  
H. Zilken
Keyword(s):  
Time Dependent ◽  
Clear Sky ◽  
Photolysis Frequencies ◽  
Model Predictions ◽  
Complex Construction ◽  
Sky Conditions ◽  
Atmosphere Simulation Chamber ◽  
Radiometric Determination ◽  
Simulation Chamber

Abstract. In this work diurnal and seasonal variations of mean photolysis frequencies for the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich are calculated. SAPHIR has a complex construction with UV permeable teflon walls allowing natural sunlight to enter the reactor volume. The calculations are based on external measurements of solar spectral actinic flux and a model considering the time-dependent impact of shadows from construction elements as well as the influence of the teflon walls. Overcast and clear-sky conditions are treated in a consistent way and different assumptions concerning diffuse sky radiance distributions are tested. Radiometric measurements inside the chamber are used for an inspection of model predictions. Under overcast conditions we obtain 74% and 67% of external values for photolysis frequencies j(NO2) (NO2+hν→NO+O(3P)) and j(O1D) (O3+hν→O2+O(1D)), respectively. On a clear sky summer day these values are time-dependent within ranges 0.65–0.86 and 0.60–0.73, for j(NO2) and j(O1D), respectively. A succeeding paper (Bohn et al., 2004) is dealing with an on-road test of the model approach by comparison with photolysis frequencies from chemical actinometry experiments within SAPHIR.

scholarly journals Technical Note: Intercomparison of formaldehyde measurements at the atmosphere simulation chamber SAPHIR

2007 ◽  
Vol 7 (6) ◽  
pp. 15619-15650 ◽  
Author(s):  
A. Wisthaler ◽  
E.C. Apel ◽  
J. Bossmeyer ◽  
A. Hansel ◽  
W. Junkermann ◽  
...  
Keyword(s):  
Ambient Air ◽  
Proton Transfer Reaction ◽  
Technical Note ◽  
Research Centre ◽  
Mixing Ratios ◽  
Analytical Instruments ◽  
Chamber Volume ◽  
Set Up ◽  
Atmosphere Simulation Chamber ◽  
Simulation Chamber

Abstract. The atmosphere simulation chamber SAPHIR at the Research Centre Jülich was used to test the suitability of state-of-the-art analytical instruments for the measurement of gas-phase formaldehyde (HCHO) in air. Five analyzers based on four different sensing principles were deployed: a differential optical absorption spectrometer (DOAS), cartridges for 2,4-dinitro-phenyl-hydrazine (DNPH) derivatization followed by off-line high pressure liquid chromatography (HPLC) analysis, two different types of commercially available wet chemical sensors based on Hantzsch fluorimetry, and a proton-transfer-reaction mass spectrometer (PTR-MS). A new optimized mode of operation was used for the PTR-MS instrument which significantly enhanced its performance for on-line HCHO detection at low absolute humidities. The instruments were challenged with typical ambient levels of HCHO ranging from zero to several ppb. Synthetic air of high purity and particulate-filtered ambient air were used as sample matrices in the atmosphere simulation chamber onto which HCHO was spiked under varying levels of humidity and ozone. Measurements were compared to mixing ratios calculated from the chamber volume and the known amount of HCHO injected into the chamber; measurements were also compared between the different instruments. The formal and blind intercomparison exercise was conducted under the control of an independent referee. A number of analytical problems associated with the experimental set-up and with individual instruments were identified, the overall agreement between the methods was good.

scholarly journals Technical Note: Intercomparison of formaldehyde measurements at the atmosphere simulation chamber SAPHIR

2008 ◽  
Vol 8 (8) ◽  
pp. 2189-2200 ◽  
Author(s):  
A. Wisthaler ◽  
E. C. Apel ◽  
J. Bossmeyer ◽  
A. Hansel ◽  
W. Junkermann ◽  
...  
Keyword(s):  
Ambient Air ◽  
Proton Transfer Reaction ◽  
Technical Note ◽  
Research Centre ◽  
Mixing Ratios ◽  
Analytical Instruments ◽  
Chamber Volume ◽  
Set Up ◽  
Atmosphere Simulation Chamber ◽  
Simulation Chamber

Abstract. The atmosphere simulation chamber SAPHIR at the Research Centre Jülich was used to test the suitability of state-of-the-art analytical instruments for the measurement of gas-phase formaldehyde (HCHO) in air. Five analyzers based on four different sensing principles were deployed: a differential optical absorption spectrometer (DOAS), cartridges for 2,4-dinitrophenylhydrazine (DNPH) derivatization followed by off-line high pressure liquid chromatography (HPLC) analysis, two different types of commercially available wet chemical sensors based on Hantzsch fluorimetry, and a proton-transfer-reaction mass spectrometer (PTR-MS). A new optimized mode of operation was used for the PTR-MS instrument which significantly enhanced its performance for online HCHO detection at low absolute humidities. The instruments were challenged with typical ambient levels of HCHO ranging from zero to several ppb. Synthetic air of high purity and particulate-filtered ambient air were used as sample matrices in the atmosphere simulation chamber onto which HCHO was spiked under varying levels of humidity and ozone. Measurements were compared to mixing ratios calculated from the chamber volume and the known amount of HCHO injected into the chamber; measurements were also compared between the different instruments. The formal and blind intercomparison exercise was conducted under the control of an independent referee. A number of analytical problems associated with the experimental set-up and with individual instruments were identified, the overall agreement between the methods was fair.

Determination of the activity meter calibration factor for Rhenium-188

2018 ◽  
Vol 173 (9-10) ◽  
pp. 758-762
Author(s):  
S. Liverani ◽  
S. Vichi ◽  
F. Zagni ◽  
S. Riga ◽  
G. M. Lima ◽  
...  
Keyword(s):  
Calibration Factor

scholarly journals Investigation of the β-pinene photooxidation by OH in the atmosphere simulation chamber SAPHIR

2016 ◽  
Author(s):  
Martin Kaminski ◽  
Hendrik Fuchs ◽  
Ismail-Hakki Acir ◽  
Birger Bohn ◽  
Theo Brauers ◽  
...  
Keyword(s):  
Degradation Mechanism ◽  
Degradation Process ◽  
Product Distribution ◽  
High Reactivity ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Emission Rates ◽  
Photochemical Degradation ◽  
Atmosphere Simulation Chamber ◽  
Simulation Chamber

Abstract. Beside isoprene, monoterpenes are the non-methane volatile organic compounds (VOC) with the highest global emission rates. Due to their high reactivity towards OH, monoterpenes can dominate the radical chemistry of the atmosphere in forested areas. In the present study the photochemical degradation mechanism of β-pinene was investigated in the Jülich atmosphere simulation chamber SAPHIR. The focus of this study is on the OH budget in the degradation process. Therefore the SAPHIR chamber was equipped with instrumentation to measure radicals (OH, HO2, RO2), the total OH reactivity, important OH precursors (O3, HONO, HCHO), the parent VOC beta-pinene, its main oxidation products, acetone and nopinone, and photolysis frequencies. All experiments were carried out under low NOx conditions (≤ 2 ppb) and at atmospheric beta-pinene concentrations (≤ 5 ppb) with and without addition of ozone. For the investigation of the OH budget, the OH production and destruction rates were calculated from measured quantities. Within the limits of accuracy of the instruments, the OH budget was balanced in all β-pinene oxidation experiments. However, even though the OH budget was closed, simulation results from the Master Chemical Mechanism 3.2 showed that the OH production and destruction rates were underestimated by the model. The measured OH and HO2 concentrations were underestimated by up to a factor of two whereas the total OH reactivity was slightly overestimated because of the poor reproduction of the measured nopinone by the model by up to a factor of three. A new, theory-derived first-generation product distribution by Vereecken and Peeters was able to reproduce the measured nopinone time series and the total OH reactivity. Nevertheless the measured OH and HO2 concentrations remained underestimated by the numerical simulations. These observations together with the fact that the measured OH budget was closed suggest the existence of unaccounted sources of HO2.

The Effect of External Conditions on Ignition Temperature of Thermoplastic Polyurethane Elastomers

2013 ◽  
Vol 838-841 ◽  
pp. 14-17
Author(s):  
Ivana Turekova ◽  
Zuzana Szabova ◽  
Tomas Chrebet ◽  
Jozef Harangozo
Keyword(s):  
Thermal Degradation ◽  
Ignition Temperature ◽  
Thermoplastic Polyurethane ◽  
Thermo Gravimetric Analysis ◽  
Gravimetric Analysis ◽  
Polyurethane Elastomers ◽  
External Conditions ◽  
Thermoplastic Polyurethane Elastomers ◽  
The Impact

The paper reports a study of the impact of moisture and age of pellets, as well as an external condition, on the thermal degradation of the thermoplastic polyurethane elastomers. Because thermoplastic polyurethane elastomers are hydroscopic polymer, moisture will have a significant impact on thermal degradation. For determination of the effect of moisture and age were used the thermo gravimetric analysis, differential scanning calorimeter and ISO STN 871: Plastics. Determination of ignition temperature using a hot-air furnace.

scholarly journals An empirical method for absolute calibration of coccolith thickness

2017 ◽  
Author(s):  
Saúl González-Lemos ◽  
José Guitián ◽  
Miguel-Ángel Fuertes ◽  
José-Abel Flores ◽  
Heather M. Stoll
Keyword(s):  
Laboratory Data ◽  
Polarized Light ◽  
Empirical Method ◽  
Absolute Calibration ◽  
Light Spectra ◽  
Independent Determination ◽  
Data Comparability ◽  
Calibration Materials ◽  
Constant Slope

Abstract. As major calcifiers in the open ocean, coccolithophores play a key role in the marine carbon cycle. Because they may be sensitive to changing CO2 and ocean acidification, there is significant interest in quantifying past and present variations in their cellular calcification by quantifying the thickness of the coccoliths or calcite plates that cover their cells. Polarized light microscopy has emerged as a key tool for quantifying the thickness of these calcite plates, but the reproducibility and accuracy of such determinations has been limited by the absence of suitable calibration materials in the thickness range of coccoliths (0–4 microns). Here, we describe the fabrication of a calcite wedge with a constant slope over 15 this thickness range, and the independent determination of calcite thickness along the wedge profile. We show how the calcite wedge provides more robust calibrations in the 0 to 1.55 μm range than previous approaches using rhabdoliths. We show the particular advantages of the calcite wedge approach for developing equations to relate thickness to the interference colors that arise in calcite in the thickness range between 1.55 and 4 μm. The calcite wedge approach can be applied to develop equations relevant to the particular light spectra and intensity of any polarized light microscope system and could significantly improve within and inter-laboratory data comparability.

scholarly journals Atmospheric photochemistry of aromatic hydrocarbons: OH budgets during SAPHIR chamber experiments

2014 ◽  
Vol 14 (13) ◽  
pp. 6941-6952 ◽  
Author(s):  
S. Nehr ◽  
B. Bohn ◽  
H.-P. Dorn ◽  
H. Fuchs ◽  
R. Häseler ◽  
...  
Keyword(s):  
Aromatic Hydrocarbons ◽  
Oh Radical ◽  
Reference Compound ◽  
Photo Oxidation ◽  
Average Ratio ◽  
Budget Analysis ◽  
Benzene Toluene ◽  
Experimental Errors ◽  
Atmosphere Simulation Chamber ◽  
Simulation Chamber

Abstract. Current photochemical models developed to simulate the atmospheric degradation of aromatic hydrocarbons tend to underestimate OH radical concentrations. In order to analyse OH budgets, we performed experiments with benzene, toluene, p-xylene and 1,3,5-trimethylbenzene in the atmosphere simulation chamber SAPHIR. Experiments were conducted under low-NO conditions (typically 0.1–0.2 ppb) and high-NO conditions (typically 7–8 ppb), and starting concentrations of 6–250 ppb of aromatics, dependent on OH rate constants. For the OH budget analysis a steady-state approach was applied in which OH production and destruction rates (POH and DOH) have to be equal. The POH were determined from measurements of HO2, NO, HONO, and O3 concentrations, considering OH formation by photolysis and recycling from HO2. The DOH were calculated from measurements of the OH concentrations and total OH reactivities. The OH budgets were determined from DOH/POH ratios. The accuracy and reproducibility of the approach were assessed in several experiments using CO as a reference compound where an average ratio DOH/POH = 1.13 ± 0.19 was obtained. In experiments with aromatics, these ratios ranged within 1.1–1.6 under low-NO conditions and 0.9–1.2 under high-NO conditions. The results indicate that OH budgets during photo-oxidation experiments with aromatics are balanced within experimental accuracies. Inclusion of a further, recently proposed OH production via HO2 + RO2 reactions led to improvements under low-NO conditions but the differences were small and insignificant within the experimental errors.

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