the smell of thunderstorms

[samba]

Hi guys,

 

I was wondering what is that smell before a thunderstorm comes after dry weather. Its very distinctive here in Australia in the summer. I remember hearing someone say it was actually ozone from the lightning; i'm not very familiar with the smell of ozone. However it could be that as I've smelt it from storms that aren't actually raining much, or are only raining far away, and furthermore the smell seems to lessen once the storm has passed or it begins to rain heavily, which seems to suggest it is produced inside the cloud itself. At it's strongest it is a smell that's reminiscent of urine(!) which is why I had originally thought it could be water+organics in soil (urea, ammonia?).

 

I was just reading the very interesting thread ongood and bad chemical smells and would have added to it with this question, but thought it was a bit off topic.

 

thanks!

 

samba

[DrDNA]

I've heard that it is ozone too, but think it is more likely that it is just from the rise in humidity and moistened things getting carried ahead of the storm in the wind.

[Mr Skeptic]

It could be ions. Given a large electric field like that of a thundercloud, some ions are formed on sharp objects, sometimes enough to make them glow blue. NOx and O3 could also be formed I think.

[gonelli]

The smell probably wouldn't be that of ozone as before the lightning storm there would be little or no ozone present as no lightning occured. And even with lightning I don't think enough ozone would be made for a people to smell.

 

I recall hearing something similar to what DrDNA said, that the smell is from a rise in humidy causing a release of chemicals from soil/plants or something simimlar to that.

[gonelli]

The smell probably wouldn't be that of ozone as before the lightning storm there would be little or no ozone present as no lightning occured. And even with lightning I don't think enough ozone would be made for a people to smell.

 

I recall hearing something similar to what DrDNA said, that the smell is from a rise in humidy causing a release of chemicals from soil/plants or something simimlar to that.

[gcol]

I read, many years ago, that it was caused by dormant spores in dry soil being activated by precipitation, becoming airborne. You will notice the aroma if you are downwind only, as they are carried by the wind preceeding the rain. Some people seem especially sensitive to the smell. I have often smelled it on an otherwise fine day, and been able to predict oncoming rain to other peoples surprise and scepticism.

[samba]

Yes, now I think of it, the smell is too strong to be created by lightning or other random events in the cloud itself. I suppose then that the smell created by spores and organic matter as you describe would be too complex to put down to a mix of one or two chemicals. Would it be an assumption to say it was the nitrogenous ones that were the stinkiest?

[imp]

Good explanation as any I've seen came from one of my lecturers at University of Nevada. I had noted this smell was most obvious in the arid desert area, far more so than the wet Midwestern geography I had grown up in. He believed the desert plants being deprived of water for many weeks, sometimes months, had developed a mechanism by which they sensed increases in relative humidity which occurred during "monsoon season", and the plants' pores opened to admit wet air into the surface cells, at the same time releasing the odors predominant in desert plants.

 

Cutting open various desert plants seemed to confirm that their natural odors greatly resembled that before-the-storm smell. imp

[jdurg]

Well don't forget that ozone is a very strong smell so you don't need a lot of it to notice the odor. (Though you get a better whiff of it if you walk into a room with old photocopiers or other electronic devices). In addition to an ozone smell, you can also smell various nitrogen oxides which are created when lightning strikes. These are typically the smells I notice once a thunderstorm has passed. I've honestly not noticed any odors prior to a thunderstorm approaching.