Water Vapor Levels Research Articles

Eocene Arctic Climate

GEOLOGY The climate of the Eocene (57.8 to 36.6 million years ago) was so warm that deciduous conifers lived in the Arctic. Despite this warmth, it is unclear what other environmental conditions prevailed to allow coniferous forests to survive through 4 months of continuous daylight during the summer and 4 months of uninterrupted darkness during the winter. Jahren and Sternberg measured the oxygen and hydrogen isotopic compositions of the cellulose from a suite of astoundingly well-preserved fossilized Metasequoia trees that grew 45 million years ago at latitudes of 80°N, near what is now Nunavit, Canada. This allowed them to determine local Eocene atmospheric moisture levels. They also estimated mean annual surface air temperatures by determining the oxygen isotopic composition of secondary carbonates in the fossilized wood. Eocene atmospheric moisture levels were 20 to 120% higher than modern Arctic values, and the mean annual temperature was more than 13°C. These warm temperatures could have increased moisture delivery to high latitudes, and high water vapor levels would have helped to maintain the warmth, particularly through the dark polar winters. These paleotemperatures and relative humidity values are like those of the spring climate of the seasonal rainforests of the North American Pacific Northwest, where relatives of these ancient Metasequoia now grow.— HJS Geology 31 , 463 (2003).

The role of the subelytral spiracles in respiration in the flightless dung beetle Circellium bacchus.

The role of the subelytral cavity in flightless beetle species as an adaptation to water saving in arid habitats is still in dispute. We found that relatively little CO(2) was released from the subelytral cavity of a large apterous beetle Circellium bacchus during simultaneous measurements of CO(2) emission from the anterior mesothoracic spiracles and posterior body, which included the subelytral spiracles. However, when we sampled air directly from inside the subelytral cavity, we discovered that this pattern was reversed. A discontinuous gas exchange cycle (DGC) was recorded from the posterior body half, revealing a flutter phase that had been absent from the anterior mesothoracic DGC. The anterior mesothoracic and posterior subelytral spiracles act in synchrony to maintain high CO(2) and water vapour levels inside the subelytral cavity. In addition, the O(2) concentration of the air within the subelytral cavity is lower than the air around the elytral case, irrespective of the time of sampling. These findings lead us to conclude that the subelytral spiracles work in a coordinated fashion with the anterior spiracles to create a DGC, which allows us to extend the hypothesis of the function of the subelytral cavity as a respiratory water-saving device.

Relating changes in agricultural practices to increasing dew points in extreme Chicago heat waves

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 24:243-254 (2003) - doi:10.3354/cr024243 Relating changes in agricultural practices to increasing dew points in extreme Chicago heat waves David Changnon*, Michael Sandstrom, Charles Schaffer Meteorology Program, Department of Geography, Northern Illinois University, DeKalb, Illinois 60115, USA *Email: changnon@geog.niu.edu ABSTRACT: The temporal distribution of surface atmospheric water vapor levels during shortduration extreme heat events at Chicago was assessed. Heat events were characterized by at least 3 consecutive days with a minimum temperature greater than 24°C (75°F) and a maximum temperature greater than 35°C (95°F). Thirteen such heat events were identified during the 75 yr (1928-2002) record at Chicago Midway Airport located inside the city. Average dew points in events fluctuated considerably over time, but generally increased. Event average hourly dew-point values before the mid 1980s were generally below 21°C, rising to an average of 24°C during the mid 1990s. The temporal changes in dew-point values were related to 2 factors: (1) the existence of average to above-average regional precipitation anomalies occurring in May and during the 20 d period prior to the heat event, and (2) changes in agricultural practices that have led to enhanced evapotranspiration rates in the Midwest. KEY WORDS: Short-duration heat waves · Surface dew-point temperature · Chicago · Climate variability · Evapotranspiration Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 24, No. 3. Online publication date: September 19, 2003 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2003 Inter-Research.

Tropospheric ozone climatology over Peninsular Malaysia from 1992 to 1999

We present the climatology of tropospheric ozone over Peninsular Malaysia in tropical Asia for the 8 years from 1992 through 1999 as measured by ozonesondes twice a month. The mean ozone concentrations in vertical profile were in the same range (30–40 ppbv) as those observed at Watukosek, Indonesia, and were lower than those at Natal, Brazil, South America, and at Brazzaville, Congo, Africa, indicating that air masses over Peninsular Malaysia are primarily influenced by the maritime environment and deep convection, as shown by the significant levels of water vapor in the middle troposphere throughout the year. Seasonally averaged ozone concentrations were highest in December, January, and February (DJF) from 6 to 7.5 km altitude and in March, April, and May (MAM) at all other heights and were lowest in June, July, and August (JJA) and September, October, and November (SON), excluding 1994 and 1997, at all heights. The ozone enhancements during DJF in the middle troposphere could be caused by depression of the deep convection because of the positive temperature anomaly and negative water vapor anomaly. The ozone enhancements above the middle troposphere (>5 km) in MAM, especially in 1997 and 1998, could be predominantly attributed to photochemical production from enhanced ozone precursor gases of Northern Hemisphere origin, especially biomass burning in continental Southeast Asia. Large ozone enhancements as high as 10–20 Dobson units observed during SON of 1994 and 1997 were associated with large‐scale biomass burnings in Indonesia.

Characterization of a cross-reactive electronic nose with vapoluminescent array elements.

A three-channel cross-reactive sensor array based on vapoluminescent platinum(II) double salt materials has been characterized. Two arrays were studied, one consisting of [Pt(CN-cyclododecyl)4][Pt(CN)4] (1), [(phen)Pt(CN-cyclohexyl)2][Pt(CN)4] (2), and [Pt(CN-n-tetradecyl)4][Pt-(CN)4] (3) materials, where phen = 1,10-phenanthroline, and a second array that has compound 3 replaced by the mixed double salt material [(phen)Pt(CN-cyclododecyl)Cl)]2[(phen)Pt(CN-cyclododecyl)2]2[Pt(CN)4]3 (4). Compounds 2, 3 and 4 are characterized here for the first time. Inclusion of solvent vapors into these materials often leads to dramatic shifts in their solid-state absorption and luminescence spectra. In these studies the arrays were exposed to a set of 10 test solvent vapors to determine the ability of each cross-reactive array to give reproducible vapoluminescent spectra characteristic of each solvent vapor. It was discovered that temperature programming between solvent vapor exposures greatly improved the reproducibility of the luminescence spectra obtained. A statistical analysis of three-dimensional resolution factors between pairs of solvent clusters in principal component space supported this assertion. The success of the temperature programming protocol was limited by the thermal stability and the sensitivity to low background water vapor levels of some platinum(II) double salt materials. The ability of the cross-reactive sensor array to differentiate between two different solvent vapors over a large concentration range was also investigated. Acetone and methanol were found to occupy two distinct regions of the three-dimensional principal component space. Detection limits for acetone and methanol were estimated from the principal component analysis as 75 and 6 g/m3, respectively.

Isomerization of alkanes and alkenes on molybdenum oxides

Isomerization of light alkanes and alkenes was investigated on pure MoO 3 powder which was gradually reduced under a rapid flow of hydrogen (1 atm) at 350 °C. Incompletely reduced MoO 3 samples readily isomerize alkanes in the order nC 4⪡ nC 5< nC 6= nC 7= nC 8. The rates are at least as high as those measured on platinum metal. Isomerization of olefins is always faster than those of the corresponding alkanes. As a consequence of the inhibiting effect of water vapor on the reduction of the molybdenum oxides, very small MoO 3 samples exhibit short-lived isomerization properties whereas larger samples whose reduction gives rise to higher water vapor level are more longer active. With all hydrocarbons marked poisoning effects by hydrocarbonaceous deposits take place. Physical adsorption of nitrogen and argon at −195 °C shows that the samples become microporous on reduction. X-ray analysis of reactive samples always reveal the presence of two molybdenum oxides, i.e. MoO 2 and an up-to-now undetermined oxide MoO x , which is known to form only at low temperatures; in addition large amounts of amorphous materials are always present. XPS analysis and the catalytic results suggest that the suboxides containing only Mo 6+ and Mo 5+ ions are not responsible for the isomerization; then the formation of the isomerizing sites results from a deeper reduction state of the MoO 3 sample. Many features of the reaction are in favor of a mechanism of the bifunctional acid type.

The 1.27‐μm O2 continuum absorption in O2/CO2 mixtures

The collision‐induced, near‐infrared O2 continuum band overlapping the weak a1Δg−X3Σg−, v = 0−0, 1.27 μm discrete band of O2 has been investigated in O2/CO2 mixtures at room temperature (T = 296 K) for total densities from 1.8 to 9.3 times that of an ideal gas under standard conditions (T = 273.15 K and P = 101.325 kPa), i.e., from 1.8 to 9.3 amagats. Absorption spectra were recorded at 0.5 cm−1 resolution using a Fourier transform spectrometer and an 84‐m pathlength. A least squares analysis of the integrated band strength, Stotal = SO2ρO2 + SO2 − O2 ρO22 + SO2 − CO2ρO2ρCO2, as a function of the carbon dioxide density, ρCO2, and the oxygen density, ρ02, yields SO2‐Co2 = 2.953(32) × 10−43 cm−2 (molecule/cm3)−2 (i.e., 2.132(23) × 10−4 cm−2 amagat−2). The SO2‐CO2 coefficient is ∼3 times greater than the corresponding SO2‐N2 coefficient determined from studies of O2/N2 mixtures, illustrating the efficiency of large electric multipolar moments in inducing continuum absorption in the 1.27‐μm band of O2. The results support the calculations by Brown and Tipping [2000], which demonstrate the importance of water, with its large electric dipole moment, in enhancing the collision‐induced absorption bands of O2 and N2 in the atmosphere. We suggest that the apparent inability of radiative transfer models to accurately account for the increased atmospheric absorption present when water vapor levels increase may be due in part to the neglect of the intensity enhancement of a number of continuum bands and of the far wings of discrete bands by water molecule collisions.

Onset, extent, and duration of dehydration in the southern hemisphere polar vortex

Satellite observations of water vapor and aerosol extinction along with temperature trajectory calculations are analyzed for the Southern Hemisphere winter of 1992 in order to determine the onset, extent, and duration of dehydration within the polar vortex. Our investigation uses measurements of water vapor from the Microwave Limb Sounder (MLS) and aerosol extinction from the Cryogenic Limb Array Etalon Spectrometer (CLAES), both on board the Upper Atmosphere Research Satellite (UARS). Evidence of persistent ice cloud formation, supported by temperature statistics obtained from air parcel trajectories, suggests that the onset of the dehydration process occurs between late June and early July. By late August‐early September water vapor depleted areas within the vortex no longer coincide with high aerosol extinctions, indicating that severe dehydration has occurred with the irreversible removal of water vapor over vast areas. Areas with depleted levels of water vapor, below the prewinter values, persist well into November. Evidence for dehydration is found on potential temperature surfaces from 420 K (the lower limit of the MLS measurements) to 520 K (approximately 16 to 22 km). The horizontal extent of the dehydrated area at 465 K encompasses up to 35% of the total vortex area equatorward of 80°S. A comparison of CLAES aerosol extinction measurements and model calculations of aerosol extinction suggests an average ice particle number concentration and size of 10−2–10−3 cm−3 and 10–30 μm, respectively. We show that the difference between the timing of the onset of dehydration found here and that in a recent analysis of Polar Ozone and Aerosol Measurement III (POAM) observations can be explained by the latitudinal sampling pattern of the POAM instrument.

Optimization study of a microwave differential technique for humidity measurement in gases

We present a simulation study of precision humidity sensing in gases by a microwave differential technique. We investigate the conditions for the optimization of the system capabilities. The small quantity at the parts per million (ppm) level of water vapor in gases is determined by measuring a shift of the resonant frequency of a measuring resonator relative to a reference one. Because of some unavoidable differences in the physical dimensions and electrical characteristics of the setup components, we studied the variation of the circuit parameters that could significantly have an impact on the sensitivity of the method. We also considered possible asymmetries between each branch of the circuit. It is concluded that our circuit design can tolerate imperfect symmetry of the components and still provide good sensitivity, as shown by our experimental results.

Study of the quantum efficiency of CsI photo-cathodes exposed to oxygen and water vapour

The operation of CsI photocathodes in gaseous detectors requires special attention to the purity of the applied gas mixtures. We have studied the influence of oxygen and water vapour contaminations on the performance of CsI photocathodes for the ALICE HMPID RICH prototype. Measurements were done through comparison of Cherenkov rings obtained from beam tests. Increased levels of oxygen and water vapour did not show any effect on the performance. The results of this study found a direct application in the way of storing CsI photocathodes over long periods and in particular in the shipment of the HMPID prototype from CERN to the STAR experiment at BNL.

The oxidation of thin foils of FeCrAl(RE) alloys in moist air

The effect of varying levels of water vapour in air on the oxidation of FeCrAl plus Reactive Element (RE) alloys has been investigated at temperatures of 1200°C and 1300°C. Thin (<125 μm) foils of three different commercial alloys (Kanthal AF, PM2000 and Aluchrom YHf) have been tested to failure in laboratory air and air containing 3.2 vol.% water vapour. At this point the protective aluminium oxide scale fails and the alloys go into breakaway oxidation with the formation of chromium- and then ironrich oxide. Our results would suggest that high levels of water vapour in the atmosphere speed up the initial oxidation and reduce the overall lifetime of the thin components. The important factor for the total scale failure, the formation of non-protective iron oxide, is the depletion of Al levels to a critical value, below which no protective alumina scale can form; and this occurred slightly faster in an air + 3.2 vol.% water vapour environment.

Apriori Process-Property Relationships of GaN Epitaxial Growth in Ga/N/H/C/O Systems

AbstractA comprehensive thermodynamic analysis has been performed for the Ga/N/H/C/O system. Apriori process-property relationships of the metal organic chemical vapor deposition (MOCVD) of Gallium Nitride (GaN) are thus obtained. The parameter space for pure GaN growth is studied for system water vapor levels of 0.1 ppb – 10 ppm, system pressure between 10-6- 106 Torr, N/Ga feed ratios of 1 - 100,000, C/Ga feed ratios of 0 – 100, and H2/Ga feed ratios of 100 – 10,000. Higher growth temperatures for pure GaN are predicted at high operating pressures (for pressures greater than 0.1 Torr), low C/Ga feed ratios, high carrier gas flow rates, and mostly at low N/Ga feed ratios. Because relative C/Ga, N/Ga and H2/Ga feed ratios have been considered, the predictions in this study are applicable to any multiple and single precursor systems. Such analyses can be easily extended to the molecular beam epitaxy of GaN, when the feed ratio C/Ga = 0. Experimental data reported on the growth of GaN are found to be in good agreement with our theoretical predictions, for many systems that have included different source species.

ITAL]Submillimeter Wave Astronomy Satellite[/ITAL] Observations of Jupiter and Saturn:Detection of 557 GH[CLC]z[/CLC] Water Emission from the Upper Atmosphere

We have used the Submillimeter Wave Astronomy Satellite to carry out observations on Jupiter and Saturn in two bands centered at 489 and 553 GHz. We detect spectrally resolved 557 GHz H2O emission on both planets, constraining for the first time the residence levels of external water vapor in Jupiter's and Saturn's stratosphere. For both planets, the line appears to be formed at maximum pressures of about 5 mbar. For Jupiter, the data further show that water is not uniformly mixed but increases with altitude above the condensation level. In each planet, the amount of water implied by the data is 1.5-2.5 times larger than inferred from Infrared Space Observatory data. In addition, our observations provide new whole-disk brightness measurements of Jupiter and Saturn near 489 and 553 GHz.

Atmospheric physics. Enlightening water vapour

Water vapour in Earth's upper troposphere acts as a powerful greenhouse gas, hence the interest in monitoring variations in its concentration there. A way to do so may emerge from the finding that global lightning activity is correlated with upper tropospheric levels of water vapour.

Experimental and kinetic modeling study of the oxidation of benzene

The oxidation of benzene under flow-reactor conditions has been studied experimentally and in terms of a detailed chemical kinetic model. The experiments were performed under plug-flow conditions, at excess air ratios ranging from close to stoichiometric to very lean. The temperature range was 900–1450 K and the residence time of the order of 150 ms. The radical pool was perturbed by means of varying the concentration of water vapor and by adding NO. Furthermore, a few experiments were conducted on pyrolysis and oxidation of phenol. Benzene oxidation is initiated at ∼1000 K; the temperature for complete oxidation depends on stoichiometry, ranging from 1100 K (very lean conditions) to 1300 K (close to stoichiometric). The water vapor level and the presence of NO have only a minor impact on the temperature regime for oxidation. The proposed chemical kinetic model was validated by comparison with the present experimental data as well as flow reactor and mixed reactor data from literature. The model provides a reasonably good description of the overall oxidation behavior of benzene over the range of conditions investigated. However, before details of the oxidation behavior can be predicted satisfactorily, a number of kinetic issues need to be resolved. These include product channels and rates for the reactions of phenyl and cyclopentadienyl with molecular oxygen as well as reaction chemistry for the oxygenated cyclic compounds formed as intermediates in the oxidation process. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 498–522, 2000

The Near‐Infrared Sky Emission at the South Pole in Winter

The Antarctic plateau provides superb sites for infrared astronomy, a result of the combination of low temperatures, low levels of precipitable water vapor, high altitude, and atmospheric stability. We have undertaken measurements of the sky background from 1 to 5 μm at the South Pole, using a single channel InSb spectrometer, the Infrared Photometer Spectrometer (IRPS), during the winter (dark) period of 1995. The IRPS records the DC level of the sky flux through a 4° beam and a variety of broadband and narrowband (1%) filters. It can be scanned in elevation from horizon to horizon through the zenith. We find a 20-100 times reduction in the background of thermal emission compared to that from mid-latitude sites such as Siding Spring and Mauna Kea, with typical background levels of 80-200 μJy arcsec-2 at 2.43 μm, 100-300 mJy arcsec-2 at 3.6 μm and ~0.5 Jy arcsec-2 at 4.8 μm. Airglow emission contributes significantly to the sky flux shortward of ~2.4 μm, which is why the Kdark (2.27-2.45 μm) band emission does not drop to the 10-20 μJy arcsec-2 levels originally predicted. The darkest window for IR observations from the South Pole is from 2.35 to 2.45 μm, where the fluxes from the atmosphere may drop to as low as ~50 μJy arcsec-2 at times. Airglow dominates the emission at J (1.25 μm) and H (1.65 μm), but the flux levels of 300-600 μJy arcsec-2 and 800-2000 μJy arcsec-2, respectively, are also one-third to one-half those at temperate sites. We find no evidence for any significant contribution from auroral emission to the Kdark band. During twilight, when the Sun is <10° below the horizon, scattered sunlight contributes to the sky background with a Rayleigh-type spectrum. Scattered moonlight is also evident in the sky emission at the J band when the Moon is up.

Process‐Property Relationships of SiC Chemical Vapor Deposition in the Si/H/C/O System

A comprehensive thermodynamic analysis has been performed for the Si/H/C/O system from which a priori process‐property relationships of the chemical vapor deposition (CVD) of silicon carbide (SiC) are obtained. The parameter space for pure silicon carbide growth is reported for five orders of magnitude of the system water vapor level (1 ppb‐100 ppm), four orders of magnitude of system pressure (0.1‐760 Torr), and two orders of magnitude of C/Si feed ratio (0.25‐20) and feed ratio (50‐10,000). Lower growth temperatures for pure SiC are predicted in clean systems with low system water vapor levels, at stoichiometric to near carbon excess conditions (C/Si ≅ 1 to C/Si > 1), at high carrier gas flow rates (large feed ratios), and at low operating pressures. Because relative C/Si and feed ratios have been considered, the predictions in this study are applicable to both multiple and single precursor systems. Further, these results are valid for the CVD of α‐SiC as well as β‐SiC. Experimental data reported on the growth of α‐SiC and β‐SiC are found to be in satisfactory agreement with our theoretical predictions, for numerous systems that include multiple and single source, silicon and carbon, species. © 1999 The Electrochemical Society. All rights reserved.

Assessment of upper tropospheric HOx sources over the tropical Pacific based on NASA GTE/PEM data: Net effect on HOx and other photochemical parameters

Data for the tropical upper troposphere (8–12 km, 20°N‐20°S) collected during NASA's Pacific Exploratory Missions have been used to carry out a detailed examination of the photochemical processes controlling HOx (OH+HO2). Of particular significance is the availability of measurements of nonmethane hydrocarbons, oxygenated hydrocarbons (i.e., acetone, methanol, and ethanol) and peroxides (i.e., H2O2 and CH3OOH). These observations have provided constraints on model calculations permitting an assessment of the potential impact of these species on the levels of HOx, CH3O2, CH2O, as well as ozone budget parameters. Sensitivity calculations using a time‐dependent photochemical box model show that when constrained by measured values of the above oxygenated species, model estimated HOx levels are elevated relative to unconstrained calculations. The impact of constraining these species was found to increase with altitude, reflecting the systematic roll‐off in water vapor mixing ratios with altitude. At 11–12 km, overall increases in HOx approached a factor of 2 with somewhat larger increases being found for gross and net photochemical production of ozone. While significant, the impact on HOx due to peroxides appears to be less than previously estimated. In particular, observations of elevated H2O2 levels may be more influenced by local photochemistry than by convective transport. Issues related to the uncertainty in high‐altitude water vapor levels and the possibility of other contributing sources of HOx are discussed. Finally, it is noted that the uncertainties in gas kinetic rate coefficients at the low temperatures of the upper troposphere and as well as OH sensor calibrations should be areas of continued investigation.

Feedbacks in a Simple Prognostic Tropical Climate Model

Abstract A simple four-cell model of the tropical atmosphere in equilibrium with its boundaries is introduced, which can support a variable diabatic circulation and prognostic temperature and humidity profiles. The model is used to predict atmospheric perturbations away from the observed base state. Prognostic variables include radiation, surface fluxes, and dynamic transports, with temperature and water vapor levels determined by conservation constraints. The model includes a specially developed water vapor scheme that performs favorably compared with observations. The model is used to simulate the local and nonlocal sensitivity of the tropical maritime atmosphere to changes in surface temperature and other boundary conditions at very large horizontal scales. The main findings are as follows. (i) The sensitivity of boundary layer convergence to sea surface temperature (SST) variations depends on the behavior of convective heating over cooler regions and may be overestimated by heuristic models that ignor...

Application of the Shifting Method as a Technique to Correct for the Background in Quantitative Analysis by Open-Path FTIR

ABSTRACT In open-path Fourier Transform Infrared spectroscopy, the generation of a suitable background single-beam spectrum is of major concern. The Shifting Method is a derivative-like approach to correct for the background without the need to actually measure a background spectrum using the sample single-beam spectrum. A thorough study of the Shifting Method was conducted. A set of guidelines was developed based on the results of artificial and closed cell data. These guidelines were applied to three different data sets, consisting of cell and open path data with multiple compounds, overlapping peaks, and high water vapor and aerosol levels.