I have never used this process but I have chaired a government committee reporting on the extent of surface water acidifcation from N and S oxides in the atmosphere. If there is any water in the atmosphere they form micro-droplets. Does anhydrous nitric acid exist or does it not break down into N-oxides?

Stephen

Nitric acid does exist as a, stable, gas in the atmosphere. For calibration of instruments it is produced by standard gas-permeation. This is done by leading a concentrated solution of nitric acid through a porous tube. This is trial and error. We also use the method.

However with the spray-drying technique we can very precisely make the concentration we need. We have several publications on this approach. I was just curious whether others use it for instance for other gases, potentially in other environments like off-gases

To finish: there are other soluble atmospheric trace gases for which it (would ) work, but we did not try it: ammonia, H2O2

Addition:

nitric acid is the end product of the oxidation of the nitrogen oxides in the atmosphere.

We measured nitric acid concentrations in Atlanta. In the Netherlands almost all nitric acid is neutralized by ammonia. The resulting ammonium-nitrate is a solid material, however so hygroscopic that this compound is indeed present as microdroplets. Also this investigated in great detail.

Harry

Thanks (again!), Harry. We were looking at the effects of acids on water - another committee looked at the atmospheric issues themselves. I presume your interest is in human health effects.....

Hmmm! Lucky The Netherlands has a damp atmosphere ... but I suppose here wasn't enough ammonium nitrate to set off an aerial explosion if it dried out....

Stephen

As for the damp atmosphere: ammonium-nitrate is so hygroscopic that it does not dry, not even at the lowest relative humidity .

And concentrations in the atmosphere are so low that it is far below the explosion limit. Detonation only occurs when there are large lumps of ammonium-nitrate. This happened in a chimney of an installation where it had accumulated in a bend.

Stephen

I happen to have been in acid deposition as early as 1981. So are and were many of my colleagues at the institute. One is a world expert on ammonia deposition; the other was on a US committee (I think MAAP) in the eighties.

Our instrumentation was built for the detection of acidifying gases like nitric acid. And the commercial instrument developed a few years ago was thoroughly tested in the EPA network for acid deposition in recent years at EPA-sites in the US outside Washington. This was done by the John Bowser; maybe you know his name.

Actually I was actively working in acid deposition in the 80's too. Until it was decided by our government around 1990 that we had sufficient knowledge on acidification and the support was abruptly stopped. For me reason to shift to a completely different field (coal-combustion). Then to a new field, climate change, and then to air pollution. In the latter areas the same instrumentation to measure aerosol compounds is used

In case you are interested the instrument used for measurements is the MARGA.

Forgot to mention worked in the US-acidity long-range program in 1983 during sabbatical at BNL.

Harry - I was director of the environment lab for the UK water authorities from 1980 -1987. Acid rain was a minor problem for them and we avoided it because it was a crowded field already. in 1982 I was asked to chair a government committee because the state electric power company was at war with the state-funded environment laboratories. My job was to keep the peace while we produced a report. I was a neutral with a background that meant I could pick up the science as we went along. We finished in 1984 and I left the subject then but had learned a lot and not all to do with acid rain! I left the water research centre in 1992 after the govt privatised the water authorities and spent the next 18 years working as a consultant in former communist countries, on EU, WB, or nationally funded projects.