scispace - formally typeset
SciSpace - Your AI assistant to discover and understand research papers | Product Hunt

Journal ArticleDOI

A Computer-Controlled Continuous Air Drying and Flask Sampling System

01 Apr 2004-Journal of Atmospheric and Oceanic Technology (American Meteorological Society)-Vol. 21, Iss: 4, pp 651-659

AbstractA computer-controlled continuous air drying and flask sampling system has been developed and is discussed here. This system is set up for taking air samples automatically at remote places. Twenty glass flasks can be connected one by one or in pairs, and they can be filled at preset times, after preset intervals, or by online remote control. The system is capable of drying air continuously without operator intervention, with a flow rate of up to 4 L min−1, to a dewpoint below −50°C. This enables continuous sampling, always retaining grab air samples of, for example, the last 24 h. This way, it is possible to decide afterward, according to online instrument records, if it is worthwhile to keep a single flask sample or even the whole diurnal cycle for later analysis at the laboratory. Dry sample air can be supplied to other analyzers. Four copies of the instrumentation are active at various places in Europe and have been shown to be able to run without servicing for periods of more than 1 month.

Topics: Laboratory flask (53%), Sample (material) (51%)

Summary (2 min read)

1. Introduction

  • Sampling of atmospheric whole air into glass flasks for later laboratory analysis of trace gas concentrations and isotopic ratios (commonly known as flask sampling) has proven to be a tool of major importance in global carbon cycle research (e.g., Conway et al.
  • This is unfavorable for the oxygen isotopic ratio 18O/16O in CO2, being sensitive to oxygen atom exchange with traces of water (Gemery et al. 1996), and it impairs O2/N2 measurements on the air.
  • Most networks now use preconditioned flasks; that is, flasks filled with the appropriate pressure of dry air that resembles the expected sample air as well as possible in its analyzed constituents.
  • Another kind of study requires very frequent flask sampling, for example, studies using diurnal cycle characteristics (Zondervan and Meijer 1996; Meijer et al. 1996; Takahashi et al. 2002).

2. The instrument

  • Outside air is sucked through the drying system (including a membrane predrying step), through one or more of the 20 sample flasks that is opened, to the pump.
  • Shown in Fig. 1 the air is used as a drying agent flowing from the upper-right to the upper-left connection, and the sample air from left to right.
  • The two 10-port solenoid valve manifolds (distributing the air to the single flasks) and the air collection manifold (collecting the air after flushing through any one of the flasks) are custom made from aluminium.
  • Preventing considerable dead volumes (especially enclosing all tubing between and flasks), as well as the risk of one leaking flask connection spoiling the whole series of samples, were the main reasons to have a solenoid valve in addition to the flasks’ own electrically actuated valves.
  • It handles the sampling procedure according to the user-defined protocols.

3. Example of results

  • Since the second half of 2001, four copies of the autosampler system have been deployed and are functioning within the European Union (EU) Environment and Climate project Aerocarb, which is part of the Carbo-Europe cluster of projects.
  • Some first experiments of this kind have been performed by Zondervan and Meijer (1996) and Meijer et al. (1996), and it has been decided that during two years of the the Aerocarb project automated diurnal cycle flask sampling will get full attention, at at least four different locations.
  • According to Meijer et al. (1996), the total CO2 was separated into background, biospheric, and fossil contributions, assuming constant background values and a biospheric 14C content that is equal to the atmospheric background.
  • There are also four samples clearly deviating from this mean value.

4. Conclusions

  • The authors have developed an apparatus for the continuous automatic flushing and filling of up to 20 sample flasks with dry air.
  • The flexibility of the system makes it useful for other settings as well, most notably that of periodic (e.g., once a week) flask sampling in a remote, unmanned station.
  • This would reduce the scatter on the time series and thus also increase its value for simulation study verification purposes.
  • People from their faculty’s mechanical and electrical workshops are gratefully acknowledged for their skill and helpfulness.
  • This research has been financed by the EU 5th Framework Program Environment and Climate, under Contract EVK2 CT1999 00013 , with financial contributions from the Netherlands and Hungarian Organisations for Scientific Research (NWO and OTKA) in the framework of the Hungarian–Dutch Research Cooperation (NWO 048.011.34, OTKA N31783).

Did you find this useful? Give us your feedback

...read more

Content maybe subject to copyright    Report

University of Groningen
A computer-controlled continuous air drying and flask sampling system
Neubert, R.E.M.; Spijkervet, L.L.; Schut, J.K.; Been, H. ; Meijer, H.A.J.
Published in:
Journal of Atmospheric and Oceanic Technology
DOI:
10.1175/1520-0426(2004)021<0651:ACCADA>2.0.CO;2
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from
it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date:
2004
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Neubert, R. E. M., Spijkervet, L. L., Schut, J. K., Been, H., & Meijer, H. A. J. (2004). A computer-controlled
continuous air drying and flask sampling system.
Journal of Atmospheric and Oceanic Technology
,
21
(4),
651-659. https://doi.org/10.1175/1520-0426(2004)021<0651:ACCADA>2.0.CO;2
Copyright
Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the
author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.
More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-
amendment.
Take-down policy
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately
and investigate your claim.
Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the
number of authors shown on this cover page is limited to 10 maximum.
Download date: 10-08-2022

A
PRIL
2004 651NEUBERT ET AL.
q 2004 American Meteorological Society
A Computer-Controlled Continuous Air Drying and Flask Sampling System
R. E. M. N
EUBERT
,L.L.S
PIJKERVET
,J.K.S
CHUT
,H.A.B
EEN
,
AND
H. A. J. M
EIJER
Centrum voor IsotopenOnderzoek, Groningen, Netherlands
(Manuscript received 18 March 2003, in final form 21 November 2003)
ABSTRACT
A computer-controlled continuous air drying and flask sampling system has been developed and is discussed
here. This system is set up for taking air samples automatically at remote places. Twenty glass flasks can be
connected one by one or in pairs, and they can be filled at preset times, after preset intervals, or by online
remote control. The system is capable of drying air continuously without operator intervention, with a flow rate
of up to 4 L min
21
, to a dewpoint below 2508C. This enables continuous sampling, always retaining grab air
samples of, for example, the last 24 h. This way, it is possible to decide afterward, according to online instrument
records, if it is worthwhile to keep a single flask sample or even the whole diurnal cycle for later analysis at
the laboratory. Dry sample air can be supplied to other analyzers. Four copies of the instrumentation are active
at various places in Europe and have been shown to be able to run without servicing for periods of more than
1 month.
1. Introduction
Sampling of atmospheric whole air into glass flasks
for later laboratory analysis of trace gas concentrations
and isotopic ratios (commonly known as flask sampling)
has proven to be a tool of major importance in global
carbon cycle research (e.g., Conway et al. 1994; Keeling
et al. 1995; Francey et al. 1995). In this way, air samples
can be taken even at remote places with little infrastruc-
ture (and thus anthropogenic influences), providing bet-
ter observation coverage of larger areas.
The simplest way to take a flask sample is to evacuate
a flask in the laboratory, send it to the specific location,
and have it filled by an operator by just opening the
flask valve. Although this method is still successfully
applied in one of the global networks (Keeling et al.
1995), it has some distinct disadvantages.
1) After an extended period of storage under vacuum,
the inner surface of the glass flask is definitely not
in equilibrium with the air that suddenly flows in,
leading to several kinds of superficial de- and ad-
sorption processes after evacuation and sampling,
respectively, notably for CO
2
and its isotopomeres.
2) The air is not dried. This is unfavorable for the ox-
ygen isotopic ratio
18
O/
16
OinCO
2
, being sensitive
to oxygen atom exchange with traces of water (Gem-
ery et al. 1996), and it impairs O
2
/N
2
measurements
on the air.
Corresponding author address: Dr. R. E. M. Neubert, Centrum
voor IsotopenOnderzoek (CIO), University of Groningen, Nijenborgh
4, NL-9747 AG Groningen, Netherlands.
E-mail: neubert@phys.rug.nl
3) The sample quality depends critically on the vacuum
integrity of the flask seal. Even without a leakage,
there will be fractionating permeation going on
through the applied elastomere O-rings.
All these effects tend to be more of a concern with
lower flask volume. In the Keeling et al. (1995) network
that uses 5-L flasks, the disadvantages are still man-
ageable. However, for logistical reasons and the fact that
less sample air is needed nowadays due to advancements
in instrumentations, researchers strive for smaller sam-
ple flasks (down to 0.5 L). Unfortunately, the effects
mentioned above then deteriorate the sample quality to
an unacceptable point.
Thus, sampling strategies and techniques have
changed. Most networks now use preconditioned flasks;
that is, flasks filled with the appropriate pressure of dry
air that resembles the expected sample air as well as
possible in its analyzed constituents. These glass con-
tainers are filled in the field using a flushing device,
which flushes the air at the sampling place through the
flask for a certain period (15–30 min), after being dried
by a chemical drying agent [usually magnesium per-
chlorate, Mg(ClO
4
)
2
] or by using a cryogenic cold trap
if a power supply is available. The various networks
have constructed very straightforward ‘sampling suit-
cases,’ with which a minimally trained technician can
easily and correctly perform this sampling procedure.
All this has complicated the situation somewhat, since
now some technical maintenance on the spot is neces-
sary, such as leak tests, pump and battery maintenance,
and above all frequent refreshment of the drying agent.
Typical examples are the National Oceanic and Atmo-

652 V
OLUME
21JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY
F
IG
. 1. Schematic drawing of the automatic flask sampling apparatus. After a predrying step (membrane
dryer close to the air inlet) one of the two cold traps dries the sample air to a dewpoint below 2408C,
while the other twin cold trap is regenerated at 1408C. The cryocoolers of the dewar vessels and the control
electronics are not shown here. The detailed working scheme is explained in the text.
spheric Administration/Climate Monitoring and Diag-
nostics Laboratory (NOAA/CMDL) AIRKIT for weekly
flask sampling at remote stations and their double-suit-
case aircraft sampler, capable of automatically sampling
flasks during one flight (Tans et al. 2001). The typical
sampling frequency for a flask sampling site is prefer-
ably once a week, or at least once every fortnight. De-
pending on how remote the actual location is, this re-
quires a significant amount of (traveling) time by the
person responsible for the sampling. Further require-
ments on the moment of sampling, such as a minimum
wind speed from a certain (clean air) wind sector or
hour of day interval, can normally only partially be met
by a person who can only devote part of his or her time
to this work (again depending very much on the travel
time that is required to the sampling place).
Another kind of study requires very frequent flask
sampling, for example, studies using diurnal cycle char-
acteristics (Zondervan and Meijer 1996; Meijer et al.
1996; Takahashi et al. 2002). Such sampling in diurnal
cycles even can be ‘continuous,’ as in the first two
cited references above. That is, flask sampling goes on
continuously, refilling the same flasks every 24 h, until
an atmospheric condition, favorable for the specific ex-
periment, has occurred. The confirmation that such an
‘event’ has occurred can only be drawn in hindsight
with the knowledge from online measurements. Thus,
the storage of the last 24 h of air in flasks at all times
is a necessity until confirmation is reached.
It is clear that an automated sampling apparatus sup-
plying dry air samples would have considerable advan-
tages, or would even be indispensable, for the purposes
mentioned above. We have built such an instrument. Up
to 20 flasks can be connected, a dry-air flow of up to
4 L min
21
can be supplied continuously, and the flasks
can be filled with either ambient atmospheric pressure
or with up to 150-kPa overpressure. Every flask is
closed (electrically actuated) with its own two O-ring
valves directly after flushing. The flask-filling schemes
are totally flexible, and an online connection via the
Internet or a modem and a mobile phone allows total
control over the system, as well as the monitoring of
all the critical parameters. This system is much more
sophisticated, after further development of the equip-
ment briefly described by Zondervan and Meijer (1996),
which did not meet the above-mentioned requirements.
2. The instrument
A schematic drawing of the system’s main parts is
shown in Fig. 1, and an overview photo of the instru-
mental arrangement is given in Fig. 2. Outside air is
sucked through the drying system (including a mem-
brane predrying step), through one or more of the 20

A
PRIL
2004 653NEUBERT ET AL.
F
IG
. 2. Pictorial overview of the complete installation: the valve manifolds are hidden on the backside of the solenoid valve frame; only
10 of possible 20 flasks are connected.
sample flasks that is opened, to the pump. The dry air
is then pumped out of the system again, and used as a
‘drying agent’ in the predrying system. In the follow-
ing, we will discuss the design of the different parts,
namely, the drying concept, the airflow system includ-
ing the flasks, and the electronics and software, includ-
ing some remarks on installation tests. The valves in
this drawing (shown as double triangles) are open when
shaded black.
a. The drying concept
The system is designed to be able to dry, continuously
and unattended, an airflow of up to 4 L min
21
under all
meteorological conditions. This means that an automatic
recovery of the drying mechanism must be included,
and that during the recovery another means of drying
must be provided. We chose a double cryogenic drying
system as the most straightforward solution.
To freeze out the water vapor from the sample air,
we use cold traps made of glass (drawn in the dewar
vessels). They have an outer diameter of 5 cm and a
total length of 28 cm. The airflow is forced through the
entire cold trap from top to bottom, since the air exit is
a small glass tube, with its entrance close to the bottom
of the cold trap. The glass bodies have pencil-tip-like
indentations at the top and three rows of indentations
between 2 and 6 cm from the bottom to ensure turbulent
flow and good contact of the air with the cold-trap walls.
The lower 2.5 cm are filled with 3-mm-diameter glass
spheres to prevent ice crystals falling to the bottom from
being sucked through the center tube to the cold-trap
air outlet. The lower 15 cm of the cold traps are im-
mersed in a silicone-oil-based thermofluid (M60.115.05,
Renggli, Rotkreuz, Switzerland); each in a separate 2-
L stainless steel dewar vessel. A rubber-sealed plastic–
foam–plastic sandwich lid insulates the top of the dewar
from the outside air and facilitates all connections. The
closure of the lid is very important, in order to prevent
outside water vapor from entering the dewars, as it
would gradually form a ‘drop’ of water (or ice, re-
spectively) at the bottom of the dewar and in between
the heating wires. With time, even a volumetric problem
would arise and make the thermofluid flow over. A Pt-
100 sensor measures the thermofluid temperature. The
fluid can either be cooled down to ø 2558Cbyanim-
mersion cryocooler probe (CC-65 II-R, Neslab Instru-
ments, Portsmouth, New Hampshire) or heated to
1408C by a resistance wire coil at the bottom of the
dewar. The glass cold traps are designed such that they
can take up to at least 75 g of water, which corresponds
to an airflow of 4 L min
21
with a relative humidity of
90% at 258C over a 15-h period.
At the inlet of the autosampler valve frame, there is
a cold-trap changeover valve setup, consisting of four
single solenoid valves [Fluid Automation Systems
(FAS), Versoix, Switzerland]. At a given time the sam-
ple air flows through valve A and cold trap 1 (with the
dewar vessel at 2558C) to another similar four-valve
installation and enters the solenoid valve manifold
through valve E. At the same time, a small membrane
drying pump (KNF Neuberger, Freiburg, Germany)
pumps room air through valve H, backward through cold
trap 2 (now heated to 1408C) and valve D to the water
outlet. In this way, water that was trapped in cold trap
2 in an earlier stage is removed. Theoretically, the dif-
ference between the absolute humidities in saturated air
at 408C and the laboratory air can be removed per unit

654 V
OLUME
21JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY
flushed air. However, condensation will occur in the
colder parts of the drying system and these water traces
will only be removed again with the dry warm air as
soon as the cold trap itself is dried. The energy con-
sumption of the solenoid valves keeps their body tem-
peratures during operation sufficiently high to prevent
condensation in the valves. In the following, cold trap
2 has to be prepared for drying again. Valves H and D
are closed, and dewar vessel 2 is cooled down to 2558C
again. During this process, the remaining humid air in
the tubing between valves H and F on the one side and
D and B on the other side (twice ø 0.5 m of tubing in
practice) is also effectively dried. The total regeneration
of a cold trap takes less than 12 h: 1 h heating, 9 h
flushing, and 1.5 h cooling down to 2408C (maximum
flushing temperature) is sufficient. Depending on the
environmental conditions, the cold-trap changeover
time can be extended to 18 h (our normal setting) or
even 24 h. This 18-h figure, combined with the moisture
capacity of the cold traps, makes the system suitable for
continuous dry air sampling in virtually every situation.
Still, it is favorable to remove a part of the water vapor
content already close to the air inlet of the system, es-
pecially if the inlet is far away from the autosampler,
as is the case for air inlets mounted on masts and towers.
The autosampler system is perfectly suited for the ad-
dition of a Nafion membrane predryer (MD 110-72-S,
Perma Pure, Toms River, New Jersey) close to the in-
take. A Nafion dryer consists of a polymer membrane
tube inside a stainless steel one. The membrane material
is only permeable for water vapor, which is actively
absorbed by sulfonic acid groups and moved along the
water vapor gradient. The incoming air passes through
the inner tube, while the volume between the inner and
outer tubes is flushed with dry gas in the opposite di-
rection to maintain the vapor gradient and remove the
water vapor to the waste outlet. This dry air is, in our
case, continuously supplied by the outlet of the auto-
sampler. Since the composition of this dry air is almost
identical to that of the inlet air (the dry air is actually
the inlet air from a short time before), the risk of influ-
encing the sample air composition due to eventual dif-
fusion processes through the membrane is minimized.
The dry air support to the Nafion dryer obviously re-
quires double tubing between the autosampler and the
inlet. In this arrangement, shown in Fig. 1 the air is
used as a drying agent flowing from the upper-right to
the upper-left connection, and the sample air from left
to right. The Nafion predryer removes between a half
and two-thirds of the water vapor content from the sam-
ple airstream, with the exact value depending on the
respective temperature and humidity (den Besten and
Neubert 1998). In setups with long inlet tubing, the
major advantage of using a Nafion predryer is to prevent
water vapor from condensing anywhere in the inlet line,
for example, if it is installed underground between a
tower and a laboratory building. We thereby exclude
the possibility of oxygen atomic (and thus also isotopic)
exchange between CO
2
and water close to or at the
condensation conditions (Gemery et al. 1996), which
might heavily alter the isotopic composition of atmo-
spheric CO
2
. The additional effect of lowering the water
vapor load of the drying system is also welcome, al-
though it is not strictly necessary, except under very
hot and humid sampling conditions.
The drying system has been extensively tested using
flows of heated air (to over 308C), and moisturized to
virtually 100% relative humidity. The final design of
the cold traps is able to effectively dry the air to a
dewpoint of ø2508C under all normal circumstances.
The moisture capacity of the cold traps is large enough
to make continuous operation possible (especially with
the assistance of the Nafion predryer). The drying sys-
tem is very robust and normally works error free for
several weeks without maintenance.
b. The airflow system and the flasks
The core of the airflow system is made of 6.35-mm
o.d. stainless steel tubing. The two 10-port solenoid
valve manifolds (distributing the air to the single flasks)
and the air collection manifold (collecting the air after
flushing through any one of the flasks) are custom made
from aluminium. The solenoid valves are of the same
type mentioned above. For connection purposes we use
vacuum-tight tube fittings (Swagelok, Solon, Ohio). The
tubing between the system and the flasks is 6.35-mm
Dekabon 1300 (Saint Gobain Performance Plastics,
Gembloux, Belgium), with 4.3-mm inner diameter and
a length of ø2 m per tubing. This is an aluminium
tubing, coated with a thin polyethylene layer on the
inside and a thick protective polyethylene tube on the
outside. We selected this material because it is robust
(very low risk of leak-causing damage) and yet flexible
and lightweight. Furthermore, it is easy to connect, and
thus a full set of 20 flasks can be exchanged in a short
time. Any influence on the composition of the trans-
ported air is virtually absent, as aluminium strongly re-
stricts diffusion into or out of the tubing. The relatively
large inner diameter accommodates flows of several li-
ters per minute over tens of meters with only a small
pressure gradient. Such a high flow is desirable, since
it minimizes the residence time of the air in the tubing
(in particular if the inlet point is far from the autosam-
pler). However, care must be taken to get the air into
thermal equilibrium with the room air before entering
the flasks (after all the air is cooled down to ø2558C),
as otherwise mass-dependent isotope (or gas type) frac-
tionation will occur.
The valve manifolds are made such that the dead
volumes are minimal. Preventing considerable dead vol-
umes (especially enclosing all tubing between manifold
and flasks), as well as the risk of one leaking flask
connection spoiling the whole series of samples, were
the main reasons to have a solenoid valve (manifold)
in addition to the flasks’ own electrically actuated

Figures (5)
Citations
More filters

Journal ArticleDOI
Abstract: Carbon monoxide (CO), carbon dioxide (CO2), and radiocarbon (14CO2) measurements have been made in Heidelberg from 2001 to 2004 in order to determine the regional fossil fuel CO2 component and to investigate the application of CO as a quantitative tracer for fossil fuel CO2 (CO2(foss)). The observations were compared with model estimates simulated with the regional transport model REMO at 0.5° × 0.5° resolution in Europe for 2002. These estimates are based on two available emissions inventories for CO and CO2(foss) and simplified atmospheric chemistry of CO. Both emissions inventories appear to overestimate fossil fuel emissions in the Heidelberg catchment area, in particular in summer and autumn by up to a factor of 2. Nevertheless, during meteorological conditions with high local source influence the CO/CO2(foss) emission ratios compared well with the observed atmospheric CO/CO2(foss) ratios. For a larger catchment area of several 100 km the observed CO/CO2(foss) ratio compared within better than 25% with the ratios derived from model simulations that take the transport from the sites of emission to the measurement station into account. Non-fossil-fuel CO emissions, production by volatile organic compounds, and oxidation, as well as soil uptake, turned out to add significant uncertainty to the application of CO as a quantitative fossil fuel CO2 surrogate tracer, so that 14CO2 measurements seem to be indispensable for reliable estimates of fossil fuel CO2 over the European continent. (Less)

80 citations


Cites methods from "A Computer-Controlled Continuous Ai..."

  • ...[15] An automated flask sampling system [Neubert et al., 2004] was set up in Heidelberg which enables us to consecutively fill up to twenty 2.5 liter glass containers with outside air: After drying to a dew point of about 40 C the air is flushed through one of the flasks for 1.5 hours at a flow…...

    [...]

  • ...In addition, a so-called ‘‘event sampler’’ [Neubert et al., 2004; see also Zondervan and Meijer, 1996] was used to collect small volume (4 standard liter) whole air, so-called event samples in glass flasks at a temporal resolution of 1–2 hours over a day, respectively a pollution event....

    [...]


Journal ArticleDOI
Abstract: . Since 1992 semi-continuous in-situ observations of greenhouse gas concentrations have been performed at the tall tower of Cabauw (4.927° E, 51.971° N, −0.7 m a.s.l.). Through 1992 up to now, the measurement system has been gradually extended and improved in precision, starting with CO2 and CH4 concentrations from 200 m a.g.l. in 1992 to vertical gradients at 4 levels of the gases CO2, CH4, SF6, N2O, H2, CO and gradients at 2 levels for 222Rn. In this paper the measurement systems and measurement results are described for the main greenhouse gases and CO, for the whole period. The automatic measurement system now provides half-hourly concentration gradients with a precision better than or close to the WMO recommendations. The observations at Cabauw show a complex pattern caused by the influence of sources and sinks from a large area around the tower with significant contributions of sources and sinks at distances up to 500–700 km. The concentration footprint area of Cabauw is one the most intensive and complex source areas of greenhouse gases in the world. Despite this, annual mean trends for the most important greenhouse gases, compatible with the values derived using the global network, can be reproduced from the measured concentrations at Cabauw over the entire measurement period, with a measured increase in the period 2000–2009 for CO2 of 1.90 ± 0.1 ppm yr−1, for CH4 of 4.4 ± 0.6 ppb yr−1, for N2O of 0.86 ± 0.04 ppb yr−1, and for SF6 of 0.27 ± 0.01 ppt yr−1; for CO no significant trend could be detected. The influences of strong local sources and sinks are reflected in the amplitude of the mean seasonal cycles observed at Cabauw, that are larger than the mean Northern Hemisphere average; Cabauw mean seasonal amplitude for CO2 is 25–30 ppm (higher value for lower sampling levels). The observed CH4 seasonal amplitude is 50–110 ppb. All gases except N2O show highest concentrations in winter and lower concentrations in summer, N2O observations show two additional concentration maxima in early summer and in autumn. Seasonal cycles of the day-time mean concentrations show that surface concentrations or high elevation concentrations alone do not give a representative value for the boundary layer concentrations, especially in winter time, but that the vertical profile data along the mast can be used to construct a useful boundary layer mean value. The variability at Cabauw in the atmospheric concentrations of CO2 on time scales of minutes to hours is several ppm and is much larger than the precision of the measurements (0.1 ppm). The diurnal and synoptical variability of the concentrations at Cabauw carry information on the sources and sinks in the footprint area of the mast, that will be useful in combination with inverse atmospheric transport model to verify emission estimates and improve ecosystem models. For this purpose a network of tall tower stations like Cabauw forms a very useful addition to the existing global observing network for greenhouse gases.

79 citations


Cites methods from "A Computer-Controlled Continuous Ai..."

  • ...The cryogenic vapour trap is a modified design from CIO Groningen (Neubert et al., 2004) and consists of two sets of four glass fingers with a volume of 100 ml, placed in 2-l stainless steel dewars filled with silicon thermofluid oil (Renggli, M60....

    [...]


Journal ArticleDOI
01 Nov 2010-Tellus B
Abstract: A 7-year-long data set of integrated high-precision 14 CO 2 observations combined with occasional hourly 14 CO 2 flask data from the Heidelberg sampling site is presented. Heidelberg is located in the highly populated and industrialized upper Rhine valley in southwestern Germany. The 14 CO 2 data are used in combination with hourly carbon monoxide (CO) observations to estimate regional hourly fossil fuel CO 2 (ΔFFCO 2 ) mixing ratios. We investigate three different 14 C calibration schemes to calculate ΔFFCO 2 : (1) the long-term median ΔCO/ΔFFCO 2 ratio of 14.6 ppb ppm -1 (mean: 15.5 ± 5.6 ppb ppm -1 ), (2) individual (2-)week-long integrated ΔCO/ΔFFCO 2 ratios, which take into account the large week-to-week variability of ±5.6 ppb ppm -1 (1σ; interquartile range: 5.5 ppb ppm -1 ), and (3) a calibration which also includes diurnal changes of the ΔCO/ΔFFCO 2 ratio. We show that in winter a diurnally changing ΔCO/ΔFFCO 2 ratio provides a much better agreement with the direct 14 C-based hourly ΔFFCO 2 estimates whereas summer values are not significantly improved with a diurnal calibration. Using integrated 14 CO 2 samples to determine weekly mean ΔCO/ΔFFCO 2 ratios introduces a bias in the CO-based ΔFFCO 2 estimates which can be corrected for with diurnal grab sample data. Altogether our 14 C-calibrated CO-based method allows determining ΔFFCO 2 at a semi-polluted site with a precision of approximately ±25%. DOI: 10.1111/j.1600-0889.2010.00477.x

66 citations


Cites methods from "A Computer-Controlled Continuous Ai..."

  • ...Therefore, an automated flask sampling system (Neubert et al., 2004) was used to fill grab samples....

    [...]


Journal ArticleDOI
Abstract: . We present an adapted gas chromatograph capable of measuring simultaneously and semi-continuously the atmospheric mixing ratios of the greenhouse gases CO2, CH4, N2O and SF6 and the trace gas CO with high precision and long-term stability. The novelty of our design is that all species are measured with only one device, making it a very cost-efficient system. No time lags are introduced between the measured mixing ratios. The system is designed to operate fully autonomously which makes it ideal for measurements at remote and unmanned stations. Only a small amount of sample air is needed, which makes this system also highly suitable for flask air measurements. In principle, only two reference cylinders are needed for daily operation and only one calibration per year against international WMO standards is sufficient to obtain high measurement precision and accuracy. The system described in this paper is in use since May 2006 at our atmospheric measurement site Lutjewad near Groningen, The Netherlands at 6°21´ E, 53°24´N, 1 m a.s.l. Results show the long-term stability of the system. Observed measurement precisions at our remote research station Lutjewad were: ±0.04 ppm for CO2, ±0.8 ppb for CH4, ±0.8 ppb for CO, ±0.3 ppb for N2O, and ±0.1 ppt for SF6. The ambient mixing ratios of all measured species as observed at station Lutjewad for the period of May 2007 to August 2008 are presented as well.

57 citations


Journal ArticleDOI
Abstract: . Measurements of the mole fraction of the CO2 and its isotopes were performed in Paris during the MEGAPOLI winter campaign (January–February 2010). Radiocarbon (14CO2) measurements were used to identify the relative contributions of 77% CO2 from fossil fuel consumption (CO2ff from liquid and gas combustion) and 23% from biospheric CO2 (CO2 from the use of biofuels and from human and plant respiration: CO2bio). These percentages correspond to average mole fractions of 26.4 ppm and 8.2 ppm for CO2ff and CO2bio, respectively. The 13CO2 analysis indicated that gas and liquid fuel contributed 70% and 30%, respectively, of the CO2 emission from fossil fuel use. Continuous measurements of CO and NOx and the ratios CO/CO2ff and NOx/CO2ff derived from radiocarbon measurements during four days make it possible to estimate the fossil fuel CO2 contribution over the entire campaign. The ratios CO/CO2ff and NOx/CO2ff are functions of air mass origin and exhibited daily ranges of 7.9 to 14.5 ppb ppm−1 and 1.1 to 4.3 ppb ppm−1, respectively. These ratios are consistent with different emission inventories given the uncertainties of the different approaches. By using both tracers to derive the fossil fuel CO2, we observed similar diurnal cycles with two maxima during rush hour traffic.

50 citations


Cites methods from "A Computer-Controlled Continuous Ai..."

  • ...An automatic flask sampler ( Neubert et al., 2004) and a tunable diode laser (TDL) spectrometer, developed and operated by the Laboratory of Molecular Physics for Atmosphere and Astrophysics (LPMAA, Croizé et al....

    [...]

  • ...An automatic flask sampler (Neubert et al., 2004) and a tunable diode laser (TDL) spectrometer, developed and operated by the Laboratory of Molecular Physics for Atmosphere and Astrophysics (LPMAA,Croizé et al., 2010), were installed for continuous CO2 andδ13CO2 measurements....

    [...]


References
More filters

Journal ArticleDOI
22 Jun 1995-Nature
Abstract: OBSERVATIONS of atmospheric CO2 concentrations at Mauna Loa, Hawaii, and at the South Pole over the past four decades show an approximate proportionality between the rising atmospheric concentrations and industrial CO2 emissions1. This proportionality, which is most apparent during the first 20 years of the records, was disturbed in the 1980s by a disproportionately high rate of rise of atmospheric CO2, followed after 1988 by a pronounced slowing down of the growth rate. To probe the causes of these changes, we examine here the changes expected from the variations in the rates of industrial CO2 emissions over this time2, and also from influences of climate such as El Nino events. We use the13C/12C ratio of atmospheric CO2 to distinguish the effects of interannual variations in biospheric and oceanic sources and sinks of carbon. We propose that the recent disproportionate rise and fall in CO2 growth rate were caused mainly by interannual variations in global air temperature (which altered both the terrestrial biospheric and the oceanic carbon sinks), and possibly also by precipitation. We suggest that the anomalous climate-induced rise in CO2 was partially masked by a slowing down in the growth rate of fossil-fuel combustion, and that the latter then exaggerated the subsequent climate-induced fall.

1,219 citations


"A Computer-Controlled Continuous Ai..." refers methods in this paper

  • ...Although this method is still successfully applied in one of the global networks (Keeling et al. 1995), it has some distinct disadvantages....

    [...]

  • ...In the Keeling et al. (1995) network that uses 5-...

    [...]

  • ...…atmospheric whole air into glass flasks for later laboratory analysis of trace gas concentrations and isotopic ratios (commonly known as flask sampling) has proven to be a tool of major importance in global carbon cycle research (e.g., Conway et al. 1994; Keeling et al. 1995; Francey et al. 1995)....

    [...]


Journal ArticleDOI
Abstract: The distribution and variations of atmospheric CO2 from 1981 to 1992 were determined by measuring CO2 mixing ratios in samples collected weekly at a cooperative global air sampling network. The results constitute the most geographically extensive, carefully calibrated, internally consistent CO2 data set available. Analysis of the data reveals that the global CO2 growth rate has declined from a peak of approximately 2.5 ppm/yr in 1987-1988 to approximately 0.6 ppm/yr in 1992. In 1992 we find no increase in atmospheric CO2 from 30 deg to 90 deg N. Variations in fossil fuel CO2 emissions cannot explain this result. The north pole-south pole CO2 difference increased from approximately 3 ppm during 1981-1987 to approximately 4 ppm during 1988-1991. In 1992 the difference was again approximately 3 ppm. A two-dimensional model analysis of the data indicates that the low CO2 growth rate in 1992 is mainly due to an increase in the northern hemisphere CO2 sink from 3.9 Gt C/yr in 1991 to 5.0 Gt C/yr in 1992. The increase in the north pole-south pole CO2 difference appears to result from an increase in the southern hemisphere CO2 sink from approximately 0.5 to approximately 1.5 Gt C/yr.

727 citations


"A Computer-Controlled Continuous Ai..." refers methods in this paper

  • ...…atmospheric whole air into glass flasks for later laboratory analysis of trace gas concentrations and isotopic ratios (commonly known as flask sampling) has proven to be a tool of major importance in global carbon cycle research (e.g., Conway et al. 1994; Keeling et al. 1995; Francey et al. 1995)....

    [...]


Journal ArticleDOI
01 Jan 1995-Nature
Abstract: CHANGES in the carbon isotope ratio (δ13C) of atmospheric CO2 can be used in global carbon-cycle models1–5 to elucidate the relative roles of oceanic and terrestrial uptake of fossil-fuel CO2. Here we present measurements of δ 13C made at several stations in the Northern and Southern hemispheres over the past decade. Focusing on the highest-quality data from Cape Grim (41° S), which also provide the longest continuous record, we observe a gradual decrease in δ13C from 1982 to 1993, but with a pronounced flattening from 1988 to 1990. There is an inverse relationship between CO2 growth rate6 and El Nino/Southern Oscillation (ENSO) events which is not reflected in the isotope record. Thus, for the ENSO events in 1982, 1986 and 1991–92, we deduce that net ocean uptake of CO2 increased, whereas during La Nina events, when equatorial sea surface temperatures are lower, upwelling of carbon-rich water increases the release of CO2 from the oceans. The flattening of the trend from 1988 to 1990 appears to involve the terrestrial carbon cycle, but we cannot yet ascribe firm causes. We find that the large and continuing decrease in CO2 growth starting in 19886 involves increases in both terrestrial and oceanic uptake, the latter persisting through 1992.

472 citations


"A Computer-Controlled Continuous Ai..." refers methods in this paper

  • ...…atmospheric whole air into glass flasks for later laboratory analysis of trace gas concentrations and isotopic ratios (commonly known as flask sampling) has proven to be a tool of major importance in global carbon cycle research (e.g., Conway et al. 1994; Keeling et al. 1995; Francey et al. 1995)....

    [...]


Journal ArticleDOI
01 Aug 1992-Nature
Abstract: Measurements of changes in atmospheric molecular oxygen using a new interferometric technique show that the O2 content of air varies seasonally in both the Northern and Southern Hemispheres and is decreasing from year to year. The seasonal variations provide a new basis for estimating global rates of biological organic carbon production in the ocean, and the interannual decrease constrains estimates of the rate of anthropogenic CO2 uptake by the oceans.

390 citations


ReportDOI
31 Dec 1995
Abstract: Molecular oxygen in the atmosphere is coupled tightly to the terrestrial carbon cycle by the processes of photosynthesis, respiration, and burning. This dissertation examines different aspects of this coupling in four chapters. Chapter 1 explores the feasibility of using air from sand dunes to reconstruct atmospheric O{sub 2} composition centuries ago. Such a record would reveal changes in the mass of the terrestrial biosphere, after correction for known fossil fuel combustion, and constrain the fate of anthropogenic CO{sub 2}.

119 citations


"A Computer-Controlled Continuous Ai..." refers background in this paper

  • ...However, depending on the soil conditions, variations of the biospheric oxidative ratio between 21.0 and 21.2 have been observed by Severinghaus (1995)....

    [...]

  • ...Here, a lower value might have been expected, as biospheric processes yield a mean of (21.1 6 0.05) mol mol21 (Severinghaus 1995) and CH4 burning (which is always prominently present in the fossil fuel use of the Netherlands) has an oxidative ratio of 22 mol mol21....

    [...]


Frequently Asked Questions (1)
Q1. What contributions have the authors mentioned in the paper "A computer-controlled continuous air drying and flask sampling system" ?

Neubert et al. this paper developed a computer-controlled continuous air drying and flask sampling system, which is capable of drying air continuously without operator intervention, with a flow rate of up to 4 L min21, to a dewpoint below 2508C.