Can the citrus smell affect our climate and how? (#science, #air, #smells, #plants, #greenhouse,#warming,#climate)
Almost everyone appreciates fresh air while walking in a forest or hiking. However, not many know that this is not because of oxygen, but rather due to the presence of trace organic vapours, and the most dominant once are monoterpenes.
Monoterpenes are a group of compounds we are all familiar with. For example, limonene and pinene are commonly found monoterpenes in fruits such as lemon, orange and mango. Fruiting flavours of some coffee varieties come from a particular blend of monoterpenes. However, the most substantial quantity of these compounds released to the air is not coming from plant fruiting bodies and flowers, but rather from the leaves. The best foliar emitters of monoterpenes are conifers (e.g. pines) and oaks. The annual emission rate of monoterpenes from a boreal forest is estimated to be more than 700 kg per square kilometre. This is on average close to 2 kg per day, and all that nicely sprayed into the air. And then an interesting thing happens, these organic vapours react with oxygen and other compounds, the molecules grow into a small particle, large enough to attract water in the air and serve as cloud condensation nuclei.
In other words, smells released from forests contribute to the cloud formation. You might know that there are many different clouds. In the case of monoterpenes and subsequent products, we are talking about the creation of low-altitude white clouds. Compare to the others, these clouds reflect incoming solar radiation more efficiently, and that causes a drop in the temperature.
Any natural cooling mechanism in this global warming age is good news.
The negative feedback to the greenhouse effect that monoterpenes offer in our climate system does not finish here. As our industry developed and more cars are on the road, we caused an increase in nitrogen deposition and thus global fertilisation of the soil. Even a little nitrogen added to the soil increase the monoterpenes emission rapidly (see more in our open-source scientific paper). Luckily the same happens with the rise in the ambient temperatures. So, higher temperatures and increased fertilisation, result in more white clouds and finally a cooling effect.
After all, we might have a substantial negative feedback mechanism, giving us just enough time to implement needed changes towards green technologies. And once again, oak and pine trees have proven to be our good friends.