[paul.fr]

In a recent podcast, it was stated that Pseudomonas are present in clouds. Now could this bacteria be the reason for the smell of rain?

I had always thought the the smells before and after rain was due to actinomycetes and 2-decanone (Petricho), I know this is old research and just wonder if the new finding of Pseudomonas being present also updates the old theory of the smell of rain?

[Bored chemist]

In my experience the smell of rain is only apparent after a dry spell. I think that's more consistent with the water releasing something (geosmin, or various other chemicals) from the soil. Also, rain water is pretty nearly pure- the bugs wouldn't have much to turn into "smell".

[paul.fr]

when in doubt, email a team of researchers!

Title:
 Genesis of petrichor
Authors:
 Bear, I. J.; Thomas, R. G.
Publication:
 Geochimica et Cosmochimica Acta, vol. 30, Issue 9, pp.869-879 (GeCoA Homepage)
Publication Date:
 09/1966
Origin:
 ELSEVIER
Bibliographic Code:
 1966GeCoA..30..869B


Abstract
"Petrichor", well known to mineralogists as argillaceous odour, is commonly observed as the pleasant and refreshing odour which frequently accompanies the first rains after a warm dry period. Several possible mechanisms have been considered in connection with the origin of this odour. These include the synthesis of odorous compounds on the clay or rock surface by spontaneous catalysis of atmospheric gases, the sorption of organic compounds from the atmosphere, catalytic transformation of sorbed compounds and microbial activity. Evidence is presented which suggests the atmosphere contains, as general contaminants, lipids, terpenes, carotenoids and other volatile decomposition products from animal and vegetable matter. The sorption of these compounds, or their oxygenated derivatives, by rocks and clays is controlled by the properties of the sorbent and the partial water vapour pressure of the atmosphere, low relative humidities favouring maximum uptake. Oxidation and transformation of sorbates take place on the rock surface and are accelerated by warm to hot climatic conditions. The odorous and volatile products of these processes are subsequently displaced from the pores of the rock by moisture when the relative humidity of the atmosphere approaches saturation. The possibility of a relationship between petrichor and petroleum formation is discussed.

[tony6789]

In my experience the smell of rain is only apparent after a dry spell. I think that's more consistent with the water releasing something (geosmin, or various other chemicals) from the soil. Also, rain water is pretty nearly pure- the bugs wouldn't have much to turn into "smell".

How is it that before it even rains you can smell it?

[tony6789]

wait lemme answer my own question...it is raining somewhere close to u and hasnt gotten to u yet so ur smelling wat ever smell is being given off at the place of the rain