Can you you tell me if the blue/grey moss stuff is on the trees because they...
The blue/grey stuff on your tree is called a lichen, composed of a fungus and an algae. Although lichens grow on tree bark, they are not parasitic and do not harm trees. They tend to grow rapidly when they are exposed to sunlight so the fact they are found in abundant numbers on dead or dying trees have to do with decreased foliage leading to an increase of penetrating sunlight. Lichens do no exist in polluted air so rest assured you air quality must be pretty good.
What type of tree is it? If you could send me additional pictures of the dying portions of the tree, the whole tree and close ups of some individual branches I might be able to assist in the diagnosis of the dying tree. Send to firstname.lastname@example.org. Also, I maintain an office 8-430 M-F in the courthouse in Troy if you'd like to visit.