The smell of atmospheric air subconsciously affects our mood
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- Smell perception is directly linked to our limbic system - olfactory bulbs are anatomically connected to this brain region, they are considered to be a part of it. Therefore odours are able to evoke memories and emotional responses before (or at least at the same time as) the electric signals reach neocortex, where cognition of the smell takes place. This is a unique feature among all sense perceptions that only the sense of smell has.
- Olfactory receptors are constantly interacting with atmospheric air. Atmospheric air for the olfactory system is like light for the eyes, it is a medium in which all the smells travel. Even when we are in closed spaces, the air which we breathe is atmospheric air reaching us through ventilation systems. Oxygen doesn't smell, but air, which is a mixture of gases, volatile compounds, and aerosols - does. Strong smells that we notice and react to usually come quickly and dissipate likewise, but the smell of the background air, which is subtle and lingering, is rarely noticed.
- Human olfactory system is extremely sensitive to some of the odorous compounds naturally present in the atmospheric air: ozone (smell of the air before, during, and after the storm) - olfactory threshold 7 ppb ; dimethyl sulfide (one of the chemicals responsible for the smell of the sea) - 1 ppb ; geosmin (contributes to the air smell after the rain) - 0.01 ppb .
- Environmental factors affect smell of the air, hence it changes often. Natural environmental factors influencing the smell of the air are - large water bodies, wind, rain, weather temperature, plants. I'll write more extensively about environmental factors influencing the smell of the air in a creative contribution below.
- Smell of the air likely had evolutionary importance for humans, especially having in mind water and plants. Humans were dependant on rain for survival (crucially important for harvest in agricultural communities, but also important for foraging). Additionally, the ability to smell water bodies from afar seems very important in the context of nomadic hunter-gatherer communities. This might explain why the smell of humid air blown with the wind is one of the most pleasant and most easily identifiable atmospheric odours (after plant odours). Wild plant odours lingering in the air are important in the context of foraging and keeping track of natural cycles.
- Smell of the air brings back personal, emotionally charged memories. In addition to universal responses that humans might have to atmospheric smells due to evolutionary psychology, their ability to remind of personal experiences is another, likely even more important factor affecting our emotions. Smell of the sea is likely to be associated with good times you spent at the seaside, flowery smell of warm summer night - of times when you went out late and had fun with friends in adolescence, the smell of clean winter's air - of sledding and playing in the snow in the childhood, etc. I've noticed from my own experience that atmospheric smells are especially good in bringing memories from the childhood. Smell of the air was the first thing you noticed when going outside, especially when spending time in less urbanized areas. It's somewhat synonymous with the atmosphere surrounding outdoor activities and events in the memory. And since the smell of fresh air is intrinsically positive, it seems to stick exclusively to positive memories. One might have specific, especially positive memories associated with certain shades of atmospheric air smell and therefore feel better (whether they realize it or not) when those shades of smell are present in the air.
Different ways to experimentally test this hypothesis
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Here's how atmospheric "perfume" is made