Evergreen needles act as air quality monitors

Every tree, even an evergreen, can be an air quality monitor. That's the conclusion of researchers who measured the magnetism of particulate matter on the needles of evergreen trees. That measurement, they found, correlated to general air quality, suggesting that analysis of the needles -- a relatively simple and low-cost process -- could provide a high-resolution, year-round picture of air quality.

source https://www.sciencedaily.com/releases/2020/09/200915194238.htm