There is an article in The Guardian reporting about a University of Virginia study sounding an alarm bell regarding the gradual loss of aromas in flowers due to pollution. Reportedly, scent molecules bond with pollutants and get destroyed in the process,
"This month researchers in Virginia announced that changes we've made to the atmosphere have begun to counteract the scent of flowers. It works like this: a flower exudes fragrance, each species with its own cocktail of aromatic chemicals evolved over millions of years to attract pollinating animals. Those aromatic chemicals encounter the Earth's new post-industrial atmosphere. Ozone breaks them down by
oxidation. Other pollutants bond with the chemicals, changing their scent. Pollinaters have trouble finding the plants they're looking for, and both animals and plants suffer."