Interesting paper on N deposition from vehicle exhaust in Kananaskis Country, AB Canada. Up to 23% of N in roadside mosses can be from vehicle emissions. The authors elaborate on possible consequences for the ecosystem in this nominally protected area, & by implication others with major highways; e.g., the national parks.
https://doi.org/10.1016/j.jnc.2022.126292

h/t to M Donovan, A-L Norman & ML Reid