A Computer-Controlled Continuous Air Drying and Flask Sampling System
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).
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Citations
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...[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…...
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...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....
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References
81 citations
78 citations
"A Computer-Controlled Continuous Ai..." refers background or methods in this paper
...…(13C and 18O) isotopic analysis of CO2, the dO2/N2 signal, and possible other tracers, deliver a very detailed ‘‘fingerprint’’ of the air parcel (Zondervan and Meijer 1996; Meijer et al. 1996), including, for example, the d13C signature of the fossil fuel and its oxidative ratio, that is,…...
[...]
...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)....
[...]
...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....
[...]
...This system is much more sophisticated, after further development of the equipment briefly described by Zondervan and Meijer (1996), which did not meet the above-mentioned requirements....
[...]
...The 14C signal, together with background air information, and combined with the detailed (13C and 18O) isotopic analysis of CO2, the dO2/N2 signal, and possible other tracers, deliver a very detailed ‘‘fingerprint’’ of the air parcel (Zondervan and Meijer 1996; Meijer et al. 1996), including, for example, the d13C signature of the fossil fuel and its oxidative ratio, that is, the ratio O2/CO2 when burnt....
[...]
70 citations
"A Computer-Controlled Continuous Ai..." refers background or methods in this paper
...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)....
[...]
...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....
[...]
...As one can see, there is a good correlation, with a slope of (9.4 6 0.5) ppb CO per ppm fossil CO2 for the majority of samples (open symbols), a value that is quite typical for this relation in winter in the Netherlands (Meijer et al. 1996)....
[...]
...…analysis of CO2, the dO2/N2 signal, and possible other tracers, deliver a very detailed ‘‘fingerprint’’ of the air parcel (Zondervan and Meijer 1996; Meijer et al. 1996), including, for example, the d13C signature of the fossil fuel and its oxidative ratio, that is, the ratio O2/CO2 when burnt....
[...]
61 citations
"A Computer-Controlled Continuous Ai..." refers background in this paper
...We avoided splits from occurring anywhere in the airflow, since these can cause fractionation severe enough to be noticeable in the O2/N2 signal (Manning 2001)....
[...]
53 citations
"A Computer-Controlled Continuous Ai..." refers background in this paper
...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....
[...]
...We thereby exclude the possibility of oxygen atomic (and thus also isotopic) exchange between CO2 and water close to or at the condensation conditions (Gemery et al. 1996), which might heavily alter the isotopic composition of atmospheric CO2....
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