[paul.fr]

Oh, the neighbours have been mowing their lawns today, and i have to say the smell of freshly cut grass is just devine. But what causes the smell?

[Seany]

Err.. I think the stuff inside the grass..

When the blade cuts the grass, lots of juice comes out from the grass! The liquid watery substance inside! Which the grass probably took up from the soil.. Well, I think that causes the smell? Not sure what substance it is though!

[another_someone]

There are many chemicals involved, which change as throughout the year, so that summer grass smells different (at least to my nose) than spring grass (the latter is sweeter).

[neilep]

I luff that smell too...and the freshness in the air after a downpour is great also !.....it's almost electric !!

 *hints at someone to clarify the electrical charge of after rain joy*

[Seany]

Me likes smell of candle gone out and petrol!! Oh me loves petrol smell!!!

[paul.fr]

I luff that smell too...and the freshness in the air after a downpour is great also !.....it's almost electric !!

 *hints at someone to clarify the electrical charge of after rain joy*

Neil, are you refering to the smell in the air after rain?

well if you are, the smell after rain is actually the smell of bacteria – actinomycetes – which grow in long, skinny filaments like spaghetti. They grow world-wide in damp soil. When the soil dries out, they die. But before they die, they make little eggs called “spores”.

These spores are really tough and can survive dry conditions for years. When the raindrops hit the ground, they make a mist of water and dirt, and humans breathe in the spores (and smell them).
When these bacteria are grown in a lab, they smell just the same as the smell after rain.
But where does the smell BEFORE rain come from?


Probably the best research on this was done in 1966 by CSIRO scientists, who wrote a paper called “Genesis of Petrichor”. “Petrichor” comes from “petri”, meaning “rock”, and “ichor” is the ethereal colourless fluid that was said to flow in the veins of the Greek gods. Petrichor’s proper chemical name is 2-decanone.

The scientists produced this chemical (with the correct smell) by running steam over rocks that had been left out in the open. The chemical didn’t come from bacteria or fungi, because the scientists were still able to produce the chemical even after they blasted the rocks with chemicals to kill any life forms on them. Scientists now know that trees release about 450 million tonnes of chemicals into the atmosphere each year.

They believe some of these chemicals may be absorbed into rocks, and then released whenever there is a sudden jump in humidity (such as occurs just before rain).

[Seany]

Oh golly. So the "fresh" air which we smell after rain is actually "bacterial" air?!!?

[neilep]

EXCELLENT POST PAUL !!...sorry to hijack your thread...but what about Positive Ions ?

[Seany]

Waitt!!! Whoa Neil!! What's up with your stars by your rank thing?!?!?!

[neilep]

Erhhmmm...I've PM'd ewe....

[Seany]

Yes.. Sorry.. LOL. My bad.. Err.. Heehee []