"Many people report a particular scent appearing around this time of year; some describe it as melancholy, while others associate it with more pleasant harvest-type smells."

"The scent of autumn can be as much an emotional shift as it is a herald of the waning daylight.... But where does this smell come from?... When the leaves fall, they die. As they take their last breath, they “exhale” all sorts of gases through tiny holes known as stomata. Among these compounds released are terpene and isoprenoids, common ingredients in the oils that coat plants. Terpenes are hydrocarbons, meaning their main ingredients are hydrogen and carbon. Pinene, a species of terpene, smells like — you guessed it — pine. It’s a main ingredient to the saplike resin that repairs the bark of conifers and pine trees. Occasionally, these gas molecules excreted by plants — known as volatile organic compounds — interact with variants of nitrous oxide. This can lead to ozone production, which can smell a bit like chlorine or the exhaust of a dryer vent. In addition to the release of gases contained within dying vegetation, two other effects contribute to the emotion-evoking scent that accompanies a northwest autumn breeze: decomposing plant matter, and pollutants trapped at the ground levels during the fall months. The soil in most parts of the world is rich in Geotrichum candidum, a fungus that causes rotting and decomposition of fruits and vegetables and dense plant matter. In fact, Geotrichum candidum has been sampled on all seven continents. This is just one of many species that erodes away as deceased organisms, the chemical reactions of which contribute to the smell of 'fall.'"

From "The scent of a season: Explaining the aromas of fall" (WaPo).

With my greatly diminished sense of smell, I wonder what emotions I miss. Melancholy? There's a deep dimension to autumn, and I have forgotten it.