POOR AIR, 2007

[Bob Smith]

Interestingly I happen to have a CO2 monitor with datalogger hanging around in my kit, and have been looking for a project to use this on. I'm also logging weather conditions on the top of mendip using a weather station and data logger. Any advice on which cave and suitable location within said cave that the device could be left to monitor conditions? PM me with suggestions or use this thread

 

[Peter Burgess]

Do you trust the low life that reads this forum not to go and nick your monitor, after you have published to everyone where it is?  I suggest you PM Bob, rather than make suggestions on air, so to speak!

 

[Bob Smith]

Cheers Peter, i'm sure all the low lifes are cursing you now for the loss of a potential gadget. thanks again hadn't thought about it that way.

 

[cap n chris]

Bob, CSCC/UBSS may well be able to suggest a good practical purpose for your CO2 logger but any project would probably be "your baby"; however, the main problem with CO2 tracking is that it needs to be done for years and years and years....

 

[Bob Smith]

Chris, whilst that is the case we seem to notice seasonal variations, and since I khow of no other project like this I thought it would be a start. Of course any previously collected data would be welcome, and since I am now local the long termness of this project shouldn't be too much of a problem.

 

[Cookie]

Interestingly I happen to have a CO2 monitor with datalogger hanging around in my kit, and have been looking for a project to use this on.

What kind of CO2 monitor is it? Did it cost a lot of money?

This kind of project is very worth while. It has been talked about on several occasions, but stumbled on obtaining a CO2 monitor at a sensible price. In fact you probably need several monitors to do a decent job, which means the price is even more critical.

 

[Hughie]

Bob - it might be an idea to talk to Brian Prewer, as I believe he and several others are operating weather stations on a long term basis in several Mendip regions.

If it's any use I can PM you some contact details (you probably know him, anyway).

 

[Bob Smith]

The CO2 montor is a telaire 7001 using the output to a voltage logger, whilst it is limited to reading only 10,000ppm so not great i high co2 areas, but ideal for measuring trends in areas where the co2 does not reach this level.

 

[Downer]

Ok, this thread is many months old, but itv was interesting to see that the subject of "Where does the CO2 come from" seems largely unanswered. Two things:

Firstly, the release of CO2 either by acid attacking calcium carbonate or by deposition of calcite from solution. To achieve 4% CO2 in a 10m high chamber requires .4 cu m CO2 per sq m. That's about 1Kg and corresponds to several Kg of rock either eaten away or deposited on every square meter. I think that amount of speleothem growth in a few days would be noticed and I'm pretty sure that amount of erosion would be too, though it would be a lot less obvious.

Secondly, I don't know where I picked it up but I have an idea that people used to think the CO2 came from ground air, i.e. the air in the surrounding rock is compressed by water and consequently is forced into the cave. It will, of course, be depleted in O2 and high in CO2, soil beasties being what they are. The severity would depend on the water movements in the area. Is this idea still viable? I can see that a large proportion of the air would have to be displaced if it is to work.

 

[graham]

The CO2 in caves is frequently of organic origin. A good read is the paper mentioned in the Mendip bad air thread:

Smith,S.L., and Telling,J.P., 2005. UBSS Expedition to Northern Thailand. UBSS Proceedings, 23(2) , pp 87-95.

Abstract: The 2003 UBSS expedition to Northern Thailand tested the practical use of closed-circuit oxygen rebreathers as tools to explore, survey and analyse cave atmospheres in bad air passages of Tham Tab Tao, Chiang Mai Province. 80 m of new cave passage was explored and surveyed and 22 paired readings of CO2/O2 were obtained; the first such paired measurements made in Thailand caves. The ratio of CO2 enrichment:O2 depletion (1:1.2), combined with the maximum calculated CO2 concentrations (5.1%) indicate that the microbial breakdown of organic matter is the source of bad air within the cave. The source of organic matter is largely from bat guano. It was found that although rebreathers were ideal for collecting uncontaminated cave atmosphere samples, on future expeditions lightweight carbon composite air cylinders with SCUBA regulators and nose-clamps may provide the safest and most practical way to extend future exploration.

 

[Downer]

The CO2 in caves is frequently of organic origin. A good read is the paper mentioned in the Mendip bad air thread:

Smith,S.L., and Telling,J.P., 2005. UBSS Expedition to Northern Thailand. UBSS Proceedings, 23(2) , pp 87-95.

Abstract: The 2003 UBSS expedition to Northern Thailand tested the practical use of closed-circuit oxygen rebreathers as tools to explore, survey and analyse cave atmospheres in bad air passages of Tham Tab Tao, Chiang Mai Province. 80 m of new cave passage was explored and surveyed and 22 paired readings of CO2/O2 were obtained; the first such paired measurements made in Thailand caves. The ratio of CO2 enrichment:O2 depletion (1:1.2), combined with the maximum calculated CO2 concentrations (5.1%) indicate that the microbial breakdown of organic matter is the source of bad air within the cave. The source of organic matter is largely from bat guano. It was found that although rebreathers were ideal for collecting uncontaminated cave atmosphere samples, on future expeditions lightweight carbon composite air cylinders with SCUBA regulators and nose-clamps may provide the safest and most practical way to extend future exploration.

Not sure that there's all that much bat guano in GB Think about it - 2-3% CO2 to a height of 10m is several hundreds grams of the gas per square meter: so it needs round about that amount of crap to have rotted away. That would be quite possible in a confined space collecting gases from a sump full of rotting cowsh, but it's not very realistic for a big, clean, cavern or passage. Of course there are other scenarios. There may be conditions where a great deal of polluted water passes through a cave, stealing oxygen and giving out CO2 as it goes. I'd be interested to know whether this is the mechanism in the big Mendip caves.

 

[graham]

Not that much bat guano, no but then you don't get 5.1% CO2 either. But there can be shed loads of organics in the water on Mendip, especially around Swildons.

 

[Downer]

Not that much bat guano, no but then you don't get 5.1% CO2 either. But there can be shed loads of organics in the water on Mendip, especially around Swildons.

Mostly caver-juice!

 

[graham]

Hopefully (Cookie  :doubt: ) we shall be publishing a detailed account of Swildon's water chemistry later this year by Roger Stenner that has much to say about this.

 

[Downer]

Hopefully (Cookie  :doubt: ) we shall be publishing a detailed account of Swildon's water chemistry later this year by Roger Stenner that has much to say about this.

'Scuse my ignorance, but is this going to be available on-line?

 

[graham]

Eventually.

 

[Downer]

Eventually.

Meanwhile, don't hold your breath? (There's a joke in there somewhere but I can't find it.)

It will be good to know how much sheep crap I've swallowed over the years.

 

[cap n chris]

Mint sauce? 

 

[Downer]

Mint sauce? 

Baaah! That's a new name for it.

 

[Downer]

Not that much bat guano, no but then you don't get 5.1% CO2 either. But there can be shed loads of organics in the water on Mendip, especially around Swildons.

Been thinking about this. The difference between 5% and 2% is obviously crucial if you're breathing it but it isn't particularly significant in terms of the amount of bat shit or other organics - 200gm/sq m is just as noticable as 500. So I'm wondering why it is that we usually see CO2 levels in the low percent region. CO2 formed chemically would be pretty pure, CO2 formed by anaerobic decomposition of oxygen-rich organics would too. CO2 formed by respiration is limited to the concentration of oxygen that it replaces - and the endurance of the organisms using it. But why does it usually stop at just a few percent? Is it just the tail end of a random distribution or is there a mechanism to limit it? It could tell us a bit about how and why the stuff builds up*. Just a thought.

*As could isotopic analysis - boy, this sounds fun. Just don't ask me to get the samples.