How many ion-pairs are there in normal conditions in the air?

[ORF]

Hello,

I don't know how to compute that number, but probably is a kind of reference value...

Q: How many ion-pairs are there in normal conditions* in the air?

(This is not homework, it is just out of curiosity.)

Thank you for your time.

Regards,
ORF
* 1 atm, 300K.

 

[fresh_42]

You've forgotten to mention humidity, e.g. Lenard effect in rain, snow, wind, clouds, height, $O_3$, daytime, location on earth, radioactivity, and condensation germs, esp. dust, plus a few extraterrestrial effects. Would take a while to find figures of exactly your conditions, but is basically possible. It seems that this is a whole branch in meteorology.

So the question is: What do you want to hear? Approximately 5 new pairs per second and cubic centimeter due to cosmic radiation? Under consideration of the recombination mechanism, this results in circa 1,800 ions per cubic centimeter.
(Found in a book "Encyclopedia of Medical Radiology".)

 

[ORF]

Hello,

I would be interested in a rough estimation, the order of magnitude, rather than an exact reference number.

The conditions would be:

• humidity: 90%
• no rain/snow/no clouds,
  
• no wind (inside lab),
• at sea level,
• north hemisphere,
• normal background ~100 nSv/h
  
• little of dust

Well, you mention radioactivity: I would like to know if a home-made electroscope can be discharged by a low specific-activity source ( granite, KCl ).

Thank you for your time.

Regards,
ORF

 

[fresh_42]

I think the only way to find out is to measure it. If this figure in the book $1,800 \,\,ions / cm^-3$ is correct for the usual atmosphere, then it shouldn't be too different in a lab, where there might be less natural sources, but maybe more artificial. AFAIK has e.g. concrete a higher radioactivity than normal. So whether 2,000 ions are sufficient to create a discharge effect is hard to tell without measurements. I've come across the following experiment:

of average charges in a room (per day).
However, electrical heating and cooling systems have a strong effect of several magnitudes difference. So my conclusion from reading a bit about the topic is, that there are far too many unknown variables to give a qualified answer. I think measurement is the only valid answer here.

 

[ORF]

Hello,

if the order of magnitude is 1e3 ions/cm3, it is fine: I expect a production of 1e6 ions/cm3/s (upper limit) from a weak source.

Regards,
ORF

 

[fresh_42]

Hello,

if the order of magnitude is 1e3 ions/cm3, it is fine: I expect a production of 1e6 ions/cm3/s (upper limit) from a weak source.

Regards,
ORF

For an electrical heater I've read something about 500,000 /cm^3, which is close to your estimation. Smoke and particulates are other sources. That's why I said that it depends on really many variables. I even found old physical papers (1903, not English) where they investigated the influence on electrical experiments.