We are using automated flux chambers to measure in-situ levels of methane, nitrous oxide and carbon dioxide emissions from stockpiled an composted manures. So far we are not measuring ammonia emissions, which are undoubtedly high. We are contemplating to integrate an ammonia trap in the sample line before the gas is delivered to the on-site GC. Do you know if the gas sample going through the acid trap (HCl) will alter subsequent CH4, N2O or CO2 measurements in the GC? Do you know if it is adequate to guide the gas sample through distilled water after it has gone through the acid trap to prevent damaging the GC? or altering CH4, N2O or CO2 recordings?
Dear Johannes,
For your case, I never do that together before, but I traped ammonia volatilization by semi-open static chamber and measured GHGs by static chamber and GC separately. Based on our experience, you can combine them together if the space of your flux chambers allow to accomodate and the air flows smoothly in the chambers. Meanwhile, the concentration of HCl should not be high and you need to do some recovery tests on the ammonia capature device before normal experiment. I hope you succeed.
Cheers,
Ping
Thank you Ping (I hope this is your first name) for your response. Just to be sure i understand what you mean: You suggest, that I should simply put an open beaker with HCl into the flux chamber and measure how much ammonia is captured? This would be easy to integrate into our current system but I can't see how I can calculate gas fluxes. I could do it, for example over a 24 h period, if i assume that no NH3 is captured in the HCl in a beaker that is open at the top, but I am not sure this is the case?
FYI, our chambers cover a surface area of 0.5 x 0.5 m and have 17 cm head space. Chambers are closed 32 x 10 min over a 24 h period and samples are withdrawn (and sent to the GC) at 3, 6 and 9 min after closure of the lid. Hence, there is no air flow through the chambers while the lid is closed.
I have not used flux chambers but suggest that HCl is a stronger and more volatile acid than you need. A 4% (w/v) solution of boric acid solution is a very efficient NH3 trap. As you suspect, acid in an open beaker will absorb NH3. During closed periods could you pump internal air through the boric acid trap at a known flow rate? If so you could arrange to have 3 traps that are independently 'on-line'. The NH3 collected would integrate the concentration 'ramping' rate, i.e.it would not directly measure the final (maximum) value. Trapped NH3 could be measured colorimetrically and there are NH3 ion selective electrodes that would work well in this application.
Thank you Paul for your advise, I'll have a look at boric acid. I want to use the ammonia trap during the composting of chicken manure, so NH3 emissions are high.
It might be possible to have a set-up where internal air is pumped through the acid trap during closure of the chamber, but it will change head-space volume and I'll have to have a timer/pump that is very well aligned with the main system. To be honest, I was hoping to integrate the acid trap into the existing system, as there is already a pump, known flow rate, pumping only when the lid is closed. Maybe I have to contact the GC manufacturer to find out if there is any risk of damaging the GC when using hydrochloric or boric acid. I can't see that the GC can get damaged if the gas that goes through the acid trap subsequently goes through 1 or 2 beakers of water and then through a moisture trap. Do you have any advise on this?
Dear Johannes,
Nitrous oxide is soluble in water and its solubility depends on the temperature and its concentration in the head space. Consequently, while passing the air through acidic traps, one should also take into account the nitrous oxide that gets dissolved in the aqueous phase. Alternatively, I suggest to measure ammonia separately as pointed out by Ping Huang.
Thank you Tariq,
Previous information told me that N2O is only minimally soluble in water. However, if your information is correct, this poses a problem, as the set-up would be such that the gas is first guided through the acid trap and then through a water trap to capture any acid that might be carried through and prevent damage to the GC.
Do you have any quantitative data that indicates the degree of N2O beeing absorbed by water in various conditions, or can you direct me to where I can find this information?
Thank you
Dear Johannes,
The following publication may be helpful.
Moraghan, J. T., & Buresh, R. (1977). Correction for dissolved nitrous oxide in nitrogen studies. Soil Science Society of America Journal, 41(6), 1201-1202.
I have no idea how much N2O is dissolved in water in your experimental set up. However, this needs to be measured; although this is bit lengthy procedure, it will give you the exact picture. What I suggest is that after absorbing ammonia, first shift all liquids (i.e. acid traps, water traps) separately in air-tight flasks, each flask should be provided with rubber septum for gas sampling. Equilibrate these flasks at room temperature for overnight. Then analyze the N2O in the headspace of each flask; some N2O still remains in the solution phase that you can calculate using headspace N2O data, room temperature and Bunsen absorption coefficients as described in this publication. Now, for each flask, add the values of N2O in the headspace plus the N2O dissolved in the solution phase. This will give you total amount of N2O that was dissolved in water during your sampling. Finally, after doing this correction for N2O, you can analyze ammonia that was trapped in acid.
Best Regards,
Tariq.
will HCl trap moisture from air passing through a HCl based flask. ???
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