Petrichor & Ozone

After a run of hazy and humid summer days, which is unusual for the UK, I began to become restless for rain. Where the fuck has it gone?? where has the water gone? I've checked the weather hoping for raindrops only for the timeline to be filled with big yellow circles. I want it it rain SO BAD. I just KNOW, that it is going to smell So Good.

This then had me thinking. I remember reading a while ago that the smell/chemical had a name so I decided to 'google it'. I then read some Cool Stuff so I decided to put it here ! For Future Reference ! <3

From what I have seen, there seem to be 3 factors that can create that 'rain smell'.

PETRICHOR

When first googling 'rain smell' i first found out about 'Petrichor' which lingers when rain falls after a prolonged dry spell [x].

The word is made from the greek 'petra' which means 'stone' and 'ichor' which is the fluid that flows in the veins of Gods in Greek Mythology.

A range of chemicals cause petrichor.

One is by a type of bacteria called Actinomycetes which are released. Actinomycetes grow in soil when conditions are damp and warm. The soil dries out and the bacteria produces spores in the soil and the longer it goes without rain, the more spores are created. When it finally rains, the compound geosmin (a by product of actinobacteria) is excreted by the wet soil and the moisture after the rain acts as an aerosol and the moist air easily carries the smell to our nostrils.

Another action that causes petrichor is the secretion of oils in plants. The oil is from certain plants during drell spells and it is absorbed by clay based soils and rocks. 

'Plants secrete oils in dry periods, which accumulate in rocks and soil. Rain causes smaller, volatile compounds within them, likely caused by oxidisation of fats, to be released.' [x]

All of the substances in the oils aren't fully known yet.

The term 'Petrichor' was coined in 1967 by two Australian researchers called Isabel Joy Bear and Richard G. Thomas for the journal 'Nature'.

In 2015, scientists used high speed cameras to see how the scent moved in the air.

'When a raindrop lands on a porous surface, air from the pores forms small bubbles, which float to the surface and release aerosols. Such aerosols carry the scent, as well as bacteria and viruses from the soil. Raindrops that move at a slower rate tend to produce more aerosols; this serves as an explanation for why petrichor is more common after light rains.'

OZONE

The 'clean' smell before a thunderstorm is caused by Ozone. Ozone 

Lightening can sometimes oxygen and nitrogen molecules in the atmosphere causing oxygen atoms to recombine with each other, creating O3, which then is carried by the wind to ground level. Ozone has a strong scent, that is similar to chlorine, and human noses can pick it up at a concentration as little as 10 parts per billion. However, despite it's clean smell, pure ozone is dangerous in high concentrations.

DAMP EARTH

after the rain or story, there is often a musty-earth smell left over and that is from Geosmin, which is a product responsible for the odour of the earth, a metabolic by-product of bacteria or blue-green algae.

In Greek 'Geosmin' means 'earth smell'. The human nose is extremely sensitive to Geosmin and can detect it at concentrations as low as 5 parts per trillion. It is thought that ancient humans used the scent to search for fresh pastures and food, more so after a prolonged period of famine and/or draught.

SOURCES

https://www.livescience.com/37648-good-smells-rain-petrichor.html

https://www.scientificamerican.com/article/storm-scents-smell-rain/

https://science.howstuffworks.com/nature/climate-weather/atmospheric/question479.htm
http://www.compoundchem.com/2014/05/14/thesmellofrain/
https://en.wikipedia.org/wiki/Petrichor
https://gizmodo.com/what-causes-the-smell-after-it-rains-1581967818