scholarly journals Design and performance of a Nafion dryer for continuous operation at CO<sub>2</sub> and CH<sub>4</sub> air monitoring sites

2013 ◽  
Vol 6 (5) ◽  
pp. 1217-1226 ◽  
Author(s):  
L. R. Welp ◽  
R. F. Keeling ◽  
R. F. Weiss ◽  
W. Paplawsky ◽  
S. Heckman
Keyword(s):  
Water Vapor ◽  
Ambient Air ◽  
Gas Mixing ◽  
Inlet System ◽  
Simple Method ◽  
Mixing Ratios ◽  
Peak Broadening ◽  
Order Of Magnitude ◽  
And Performance ◽  
The Impact

Abstract. In preparation for routine deployment in a network of greenhouse gas monitoring stations, we have designed and tested a simple method for drying ambient air to near or below 0.2% (2000 ppm) mole fraction H2O using a Nafion dryer. The inlet system was designed for use with cavity ring-down spectrometer (CRDS) analyzers such as the Picarro model G2301 that measure H2O in addition to their principal analytes, in this case CO2 and CH4. These analyzers report dry-gas mixing ratios without drying the sample by measuring H2O mixing ratio at the same frequency as the main analytes, and then correcting for the dilution and peak broadening effects of H2O on the mixing ratios of the other analytes measured in moist air. However, it is difficult to accurately validate the water vapor correction in the field. By substantially lowering the amount of H2O in the sample, uncertainties in the applied water vapor corrections can be reduced by an order of magnitude or more, thus eliminating the need to determine instrument-specific water vapor correction coefficients and to verify the stability over time. Our Nafion drying inlet system takes advantage of the extra capacity of the analyzer pump to redirect 30% of the dry gas exiting the Nafion to the outer shell side of the dryer and has no consumables. We tested the Nafion dryer against a cryotrap (−97 °C) method for removing H2O and found that in wet-air tests, the Nafion reduces the CO2 dry-gas mixing ratios of the sample gas by as much as 0.1 ± 0.01 ppm due to leakage across the membrane. The effect on CH4 was smaller and varied within ± 0.2 ppb, with an approximate uncertainty of 0.1 ppb. The Nafion-induced CO2 bias is partially offset by sending the dry reference gases through the Nafion dryer as well. The residual bias due to the impact of moisture differences between sample and reference gas on the permeation through the Nafion was approximately −0.05 ppm for CO2 and varied within ± 0.2 ppb for CH4. The uncertainty of this partial drying method is within the WMO compatibility guidelines for the Northern Hemisphere, 0.1 ppm for CO2 and 2 ppb for CH4, and is comparable to experimentally determining water vapor corrections for each instrument but less subject to concerns of possible drift in these corrections.

scholarly journals Design and performance of a Nafion dryer for continuous operation at CO<sub>2</sub> and CH<sub>4</sub> air monitoring sites

2012 ◽  
Vol 5 (4) ◽  
pp. 5449-5468 ◽  
Author(s):  
L. R. Welp ◽  
R. F. Keeling ◽  
R. F. Weiss ◽  
W. Paplawsky ◽  
S. Heckman
Keyword(s):  
Water Vapor ◽  
Monitoring Network ◽  
Ambient Air ◽  
Drying Methods ◽  
Inlet System ◽  
Simple Method ◽  
Mixing Ratios ◽  
Peak Broadening ◽  
Order Of Magnitude ◽  
Water Vapor Mixing Ratio

Abstract. In preparation for the routine deployment of the Earth Networks greenhouse gas monitoring network, we have designed and tested a simple method for drying ambient air to below 0.2% mole fraction H2O using a Nafion dryer. The inlet was designed for use with a Picarro model G2301 cavity ring down spectrometer (CRDS) CO2/CH4/H2O analyzer. The analyzer measures water vapor mixing ratio at the same frequency as CO2 and CH4 and then corrects for the dilution and peak broadening effects of H2O on the CO2 and CH4 mixing ratios. This analyzer is remarkably stable and performs well on water vapor correction tests, but there is potentially an added benefit of reducing the dependence on the H2O correction for long term field measurement programs. Substantially lowering the amount of H2O in the sample can reduce uncertainties in the applied H2O corrections by an order of magnitude or more, and eliminate the need to determine an instrument-specific H2O correction factor and to verify its stability over time. Our Nafion drying inlet system takes advantage of the extra capacity of the analyzer pump to redirect 30% of the dry gas exiting the Nafion to the outer shell side of the dryer and has no consumables. We tested the Nafion dryer against a cryotrap (−95 °C) method for removing H2O and found that it does not significantly alter the CO2 and CH4 dry mixing ratios of the sample gas. Systematic differences between the drying methods were at the level of 0.05 ppm in CO2 and 0.1 ppb in CH4 for the wet-air tests, well within the WMO compatibility guidelines.

Humidity-Dependent Cold Cells on the Antenna of the Stick Insect

2007 ◽  
Vol 97 (6) ◽  
pp. 3851-3858 ◽  
Author(s):  
Harald Tichy
Keyword(s):  
Water Vapor ◽  
Vapor Pressure ◽  
Partial Pressure ◽  
Systematic Study ◽  
Water Vapor Pressure ◽  
Ambient Air ◽  
Stick Insect ◽  
Proper Choice ◽  
Impulse Frequency ◽  
Order Of Magnitude

We present the first systematic study of the response of insect “cold cells” to a variation in the partial pressure of water vapor in ambient air. The cold cells on the antenna of the stick insect respond with an increase in activity when either the temperature or the partial pressure of water vapor is suddenly reduced. This double dependency does not in itself constitute bimodality because it could disappear with the proper choice of parameters involving temperature and humidity. In this study, we demonstrate that the evaporation of a small amount of water from the sensillum surface resulting from a drop in the water vapor pressure—leading to a transient drop in temperature and thus to a brief rise in impulse frequency—is the most plausible explanation for this bimodal response. We also show with an order-of-magnitude calculation that this mechanism is plausible and consistent with the amounts of water vapor potentially present on the sensillum. We hypothesize that a film of moisture collects on the hygroscopic sensillum surface at higher humidity and then tends to evaporate when humidity is lowered. The water might even be bound loosely within the cuticular wall, a situation conceivable in a sensillum that contains two hygroreceptive cells in addition to the cold cell.

scholarly journals OH reactivity and concentrations of biogenic volatile organic compounds in a Mediterranean forest of downy oak trees

2016 ◽  
Vol 16 (3) ◽  
pp. 1619-1636 ◽  
Author(s):  
N. Zannoni ◽  
V. Gros ◽  
M. Lanza ◽  
R. Sarda ◽  
B. Bonsang ◽  
...  
Keyword(s):  
Degradation Products ◽  
Ambient Air ◽  
Oxidation Products ◽  
Temperate Climate ◽  
Air Masses ◽  
Mixing Ratios ◽  
Oak Trees ◽  
Biogenic Compounds ◽  
Reactive Gases ◽  
The Impact

Abstract. Total OH reactivity, defined as the total loss frequency of the hydroxyl radical in the atmosphere, has proved to be an excellent tool to identify the total loading of reactive species in ambient air. High levels of unknown reactivity were found in several forests worldwide and were often higher than at urban sites.Our study presents atmospheric mixing ratios of biogenic compounds and total OH reactivity measured during late spring 2014 at the forest of downy oak trees of the Observatoire de Haute Provence (OHP), France. Air masses were sampled at two heights: 2 m, i.e., inside the canopy, and 10 m, i.e., above the canopy, where the mean canopy height is 5 m.We found that the OH reactivity at the site mainly depended on the main primary biogenic species emitted by the forest, which was isoprene and to a lesser extent by its degradation products and long-lived atmospheric compounds (up to 26 % during daytime). During daytime, no significant missing OH reactivity was reported at the site, either inside or above the canopy. However, during two nights we determined a missing fraction of OH reactivity up to 50 %, possibly due to unmeasured oxidation products. We confirmed that no significant oxidation of the primary species occurred within the canopy; primary compounds emitted by the forest were fast transported to the atmosphere. Finally, the OH reactivity at this site was maximum 69 s−1, which is a high value for a forest characterized by a temperate climate. Observations in various and diverse forests in the Mediterranean region are therefore needed to better constrain the impact of reactive gases over this area.

Polyalthia longifolia (False Ashoka) is an ideal choice for better air quality at kerbside locations

2020 ◽  
Author(s):  
Vidit Parkar ◽  
Savita Datta ◽  
Haseeb Hakkim ◽  
Ashish Kumar ◽  
Muhammed Shabin ◽  
...  
Keyword(s):  
Air Quality ◽  
Stomatal Conductance ◽  
Atmospheric Chemistry ◽  
Air Pollutants ◽  
Ambient Air ◽  
Area Index ◽  
Mixing Ratios ◽  
Post Monsoon ◽  
Polyalthia Longifolia ◽  
The Impact

&lt;p&gt;Tropospheric ozone is a major pollutant and it is harmful for humans at sustained exposures of 40 ppb or more in ambient air. In this study we calibrate the deposition of ozone for stomatal exchange (DO&lt;sub&gt;3&lt;/sub&gt;SE) model for &lt;em&gt;Polyalthia longifolia&lt;/em&gt; (False Ashoka), a tree that accounts for 5-20% of the urban plantations in Indian cities and subsequently use the model to estimate not only the stomatal O&lt;sub&gt;3&lt;/sub&gt; uptake by this tree but also its capability to sequester other criteria air pollutants. We discuss the impact of planting this tree on ozone precursors NOx and VOCs in a roadside plantation scenario for mitigating air pollution.&lt;/p&gt;&lt;p&gt;Stomatal conductance of &lt;em&gt;Polyalthia longifolia&lt;/em&gt; was measured, using a SC-1 Leaf Porometer, at IISER Mohali-Punjab in the NW-IGP (Northwest Indo-Gangetic Plane) which has a sub-tropical dry climate. Stomatal conductance was measured during all the four (Summer, Monsoon, Post-Monsoon, Winter) seasons, while BVOC emission fluxes were quantified using a dynamic plant cuvette during post monsoon, winter and summer season. We use ambient mixing ratios of ozone, NO, NO&lt;sub&gt;2&lt;/sub&gt;, SO&lt;sub&gt;2&lt;/sub&gt; and O&lt;sub&gt;3 &lt;/sub&gt;in combination with the meteorological parameters such as temperature, RH, soil moisture and photosynthetically active radiation (PAR) from the IISER Mohali Atmospheric chemistry facility to quantify &lt;em&gt;Polyalthia longifolia&lt;/em&gt; roadside plantations&amp;#8217; impact on urban air quality through stomatal uptake of air pollutants (primarily NO, NO&lt;sub&gt;2&lt;/sub&gt; and O&lt;sub&gt;3&lt;/sub&gt;) and BVOC emissions. &lt;em&gt;Polyalthia longifolia&lt;/em&gt; displays a number of very interesting characteristics that include being a low isoprene and monoterpene emitter, having an extremely high leaf area index thanks to its height, straight shape and dense canopy. It displays extreme resistance to drought and high vapour pressure deficits in summer allowing stomatal uptake of pollutants and evaporative cooling to continue even under unfavourable meteorological conditions.&lt;/p&gt;

scholarly journals Analytical system for stable carbon isotope measurements of low molecular weight (C<sub>2</sub>-C<sub>6</sub>) hydrocarbons

2011 ◽  
Vol 4 (6) ◽  
pp. 1161-1175 ◽  
Author(s):  
A. Zuiderweg ◽  
R. Holzinger ◽  
T. Röckmann
Keyword(s):  
Carbon Isotope ◽  
Stable Carbon Isotope ◽  
Carbon Isotope Ratio ◽  
Ambient Air ◽  
Automated System ◽  
Stable Carbon ◽  
Inlet System ◽  
Air Samples ◽  
Amount Of Substance ◽  
Mixing Ratios

Abstract. We present setup, testing and initial results from a new automated system for stable carbon isotope ratio measurements on C2 to C6 atmospheric hydrocarbons. The inlet system allows analysis of trace gases from air samples ranging from a few liters for urban samples and samples with high mixing ratios, to many tens of liters for samples from remote unpolluted regions with very low mixing ratios. The centerpiece of the sample preparation is the separation trap, which is used to separate CO2 and methane from the compounds of interest. The main features of the system are (i) the capability to sample up to 300 l of air, (ii) long term (since May 2009) operational δ13C accuracy levels in the range 0.3–0.8 ‰ (1-σ), and (iii) detection limits of order 1.5–2.5 ngC (collected amount of substance) for all reported compounds. The first application of this system was the analysis of 21 ambient air samples taken during 48 h in August 2009 in Utrecht, the Netherlands. Results obtained are generally in good agreement with those from similar urban ambient air studies. Short sample intervals allowed by the design of the instrument help to illustrate the complex diurnal behavior of hydrocarbons in an urban environment, where diverse sources, dynamical processes, and chemical reactions are present.

scholarly journals Influence of Bulk Microphysics Schemes upon Weather Research and Forecasting (WRF) Version 3.6.1 Nor'easter Simulations

2016 ◽  
Author(s):  
Stephen D. Nicholls ◽  
Steven G. Decker ◽  
Wei-Kuo Tao ◽  
Stephen E. Lang ◽  
Jainn J. Shi ◽  
...  
Keyword(s):  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Large Variability ◽  
Mixing Ratios ◽  
Simulated Precipitation ◽  
Single Moment ◽  
Double Moment ◽  
Order Of Magnitude ◽  
The Impact ◽  
Weather Research

Abstract. This study evaluated the impact of five, single- or double- moment bulk microphysics schemes (BMPS) on Weather Research and Forecasting (WRF) model (version 3.6.1) winter storm simulations. Model simulations were integrated for 180 hours, starting 72 hours prior to the first measurable precipitation in the highly populated Mid-Atlantic U.S. Simulated precipitation fields were well-matched to precipitation products. However, total accumulations tended to be over biased (1.10–2.10) and exhibited low-to-moderate threat scores (0.27–0.59). Non-frozen hydrometeor species from single-moment BMPS produced similar mixing ratio profiles and maximum saturation levels due to a common parameterization heritage. Greater variability occurred with frozen microphysical species due to varying assumptions among BMPSs regarding ice supersaturation amounts, the dry collection of snow by graupel, various ice collection efficiencies, snow and graupel density and size mappings/intercept parameters, and hydrometeor terminal velocities. The addition of double-moment rain and cloud water resulted in minimal change to species spatial extent or maximum saturation level, however rain mixing ratios tended higher. Although hydrometeor differences varied by up to an order of magnitude among the BMPSs, similarly large variability was not upscaled to mesoscale and synoptic scales.

scholarly journals The airborne mass spectrometer AIMS – Part 1: AIMS-H<sub>2</sub>O for UTLS water vapor measurements

2015 ◽  
Vol 8 (12) ◽  
pp. 13525-13565 ◽  
Author(s):  
S. Kaufmann ◽  
C. Voigt ◽  
T. Jurkat ◽  
T. Thornberry ◽  
D. W. Fahey ◽  
...  
Keyword(s):  
Water Vapor ◽  
Mass Spectrometer ◽  
Ambient Air ◽  
Reaction Scheme ◽  
Gas Discharge ◽  
Ion Source ◽  
Tunable Diode Laser ◽  
Cloud Formation ◽  
Calibration Source ◽  
Mixing Ratios

Abstract. In the upper troposphere and lower stratosphere (UTLS), the accurate quantification of low water vapor concentrations has presented a significant measurement challenge. The instrumental uncertainties are passed on to estimates of H2O transport, cloud formation and the H2O role in the UTLS energy budget and resulting effects on surface temperatures. To address the uncertainty in UTLS H2O determination, the airborne mass spectrometer AIMS-H2O, with in-flight calibration, has been developed for fast and accurate airborne water vapor measurements. We present the new setup to measure water vapor by direct ionization of ambient air. Air is sampled via a backward facing inlet that includes a bypass flow to assure short residence times (< 0.2 s) in the inlet line, which allows the instrument to achieve a time resolution of ∼ 4 Hz. From the main inlet flow, a smaller flow is extracted into the novel pressure-controlled gas discharge ion source of the mass spectrometer. The air is directed through the gas discharge region where water molecules react to form hydronium ion clusters, H3O+(H2O)n (n= 0, 1, 2), in a complex reaction scheme similar to the reactions in the D-region of the ionosphere. These ions are counted to quantify the ambient water vapor mixing ratio. The instrument is calibrated during flight using a new calibration source based on the catalytic reaction of H2 and O2 on a Pt surface to generate a calibration standard with well defined and stable H2O mixing ratios. In order to increase data quality over a range of mixing ratios, two data evaluation methods are presented for lower and higher H2O mixing ratios respectively, using either only the H3O+(H2O) ions or the ratio of all water vapor dependent ions to the total ion current. Altogether, a range of water vapor mixing ratios from 1 to 500 ppmv (mole ratio, 10−6 mol mol−1) can be covered with an accuracy between 7 and 15 %. AIMS-H2O was deployed on two DLR research aircraft, the Falcon during CONCERT (Contrail and Cirrus Experiment) in 2011, and HALO during ML-CIRRUS (Mid-Latitude Cirrus) in 2014. The comparison of AIMS-H2O with the SHARC tunable diode laser hygrometer during ML-CIRRUS shows a very good overall agreement between both instruments for the entire campaign.

scholarly journals Error characterization of CO<sub>2</sub> vertical mixing in the atmospheric transport model WRF-VPRM

2012 ◽  
Vol 12 (5) ◽  
pp. 2441-2458 ◽  
Author(s):  
R. Kretschmer ◽  
C. Gerbig ◽  
U. Karstens ◽  
F.-T. Koch
Keyword(s):  
Transport Model ◽  
Vertical Mixing ◽  
Atmospheric Model ◽  
Surface Fluxes ◽  
Model Errors ◽  
Simple Method ◽  
European Continent ◽  
Mixing Ratios ◽  
Error Characterization ◽  
The Impact

Abstract. One of the dominant uncertainties in inverse estimates of regional CO2 surface-atmosphere fluxes is related to model errors in vertical transport within the planetary boundary layer (PBL). In this study we present the results from a synthetic experiment using the atmospheric model WRF-VPRM to realistically simulate transport of CO2 for large parts of the European continent at 10 km spatial resolution. To elucidate the impact of vertical mixing error on modeled CO2 mixing ratios we simulated a month during the growing season (August 2006) with different commonly used parameterizations of the PBL (Mellor-Yamada-Janjić (MYJ) and Yonsei-University (YSU) scheme). To isolate the effect of transport errors we prescribed the same CO2 surface fluxes for both simulations. Differences in simulated CO2 mixing ratios (model bias) were on the order of 3 ppm during daytime with larger values at night. We present a simple method to reduce this bias by 70–80% when the true height of the mixed layer is known.

Instability Characteristic of a Single-Stage Centrifugal Compressor Exposed to Dry and Wet Gas

2012 ◽  
Author(s):  
Trond G. Grüner ◽  
Lars E. Bakken
Keyword(s):  
Experimental Investigation ◽  
Centrifugal Compressor ◽  
Pressure Sensors ◽  
Ambient Air ◽  
Single Stage ◽  
Performance Characteristics ◽  
Test Facility ◽  
Wet Gas ◽  
And Performance ◽  
The Impact

An experimental investigation was conducted to determine the instability and performance characteristics of a single-stage centrifugal compressor exposed to wet gas. The compressor was tested at different rotational speeds and low gas mass fractions (GMFs) in an open-loop test facility with ambient air and water. The stage consisted of a shrouded impeller with a vaneless diffuser surrounded by a symmetrical circular volute with increasing cross-sectional area. Liquid was uniformly injected into the impeller eye through multiple nozzles mounted in the inlet pipe. High-response dynamic pressure sensors flush-mounted in the diffuser were used to identify instability inception and evolution. Changes in the instability and pressure ratio characteristics at different GMFs and rotational speeds were revealed. Analysis with reference to dry gas was performed. Visual observation of the wet gas surge process at the inlet is described. Results and analysis obtained from the experimental investigation on wet gas instability are presented. The investigation contributed to knowledge concerning the impact of wet gas on the instability and performance characteristics.

scholarly journals The airborne mass spectrometer AIMS – Part 1: AIMS-H<sub>2</sub>O for UTLS water vapor measurements

2016 ◽  
Vol 9 (3) ◽  
pp. 939-953 ◽  
Author(s):  
Stefan Kaufmann ◽  
Christiane Voigt ◽  
Tina Jurkat ◽  
Troy Thornberry ◽  
David W. Fahey ◽  
...  
Keyword(s):  
Water Vapor ◽  
Mass Spectrometer ◽  
Ambient Air ◽  
Reaction Scheme ◽  
Gas Discharge ◽  
Ion Source ◽  
Tunable Diode Laser ◽  
Cloud Formation ◽  
Calibration Source ◽  
Mixing Ratios

Abstract. In the upper troposphere and lower stratosphere (UTLS), the accurate quantification of low water vapor concentrations has presented a significant measurement challenge. The instrumental uncertainties are passed on to estimates of H2O transport, cloud formation and the role of H2O in the UTLS energy budget and resulting effects on surface temperatures. To address the uncertainty in UTLS H2O determination, the airborne mass spectrometer AIMS-H2O, with in-flight calibration, has been developed for fast and accurate airborne water vapor measurements. We present a new setup to measure water vapor by direct ionization of ambient air. Air is sampled via a backward facing inlet that includes a bypass flow to assure short residence times (< 0.2 s) in the inlet line, which allows the instrument to achieve a time resolution of  ∼ 4 Hz, limited by the sampling frequency of the mass spectrometer. From the main inlet flow, a smaller flow is extracted into the novel pressure-controlled gas discharge ion source of the mass spectrometer. The air is directed through the gas discharge region where ion–molecule reactions lead to the production of hydronium ion clusters, H3O+(H2O)n (n = 0, 1, 2), in a complex reaction scheme similar to the reactions in the D-region of the ionosphere. These ions are counted to quantify the ambient water vapor mixing ratio. The instrument is calibrated during flight using a new calibration source based on the catalytic reaction of H2 and O2 on a Pt surface to generate a calibration standard with well-defined and stable H2O mixing ratios. In order to increase data quality over a range of mixing ratios, two data evaluation methods are presented for lower and higher H2O mixing ratios respectively, using either only the H3O+(H2O) ions or the ratio of all water vapor dependent ions to the total ion current. Altogether, a range of water vapor mixing ratios from 1 to 500 parts per million by volume (ppmv) can be covered with an accuracy between 7 and 15 %. AIMS-H2O was deployed on two DLR research aircraft, the Falcon during CONCERT (CONtrail and Cirrus ExpeRimenT) in 2011, and HALO during ML-CIRRUS (Mid-Latitude CIRRUS) in 2014. The comparison of AIMS-H2O with the SHARC tunable diode laser hygrometer during ML-CIRRUS shows a correlation near to 1 in the range between 10 and 500 ppmv for the entire campaign.

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