As I see it, although it is an important symptom, tremor is a difficult to use biomarker. This is because it varies so much from second to second, it's difficult to avoid the act of measuring from affecting the tremor, and it has so many facets: areas affected, frequency, amplitude, direction, etc.. That said, if you could overcome the pollution problem and you average over a suitable period, a day, say, I think you would get useful results.

Although it falls far short of meeting these ends, you might like to use my attempt at a tremor measurement tool:

http://www.parkinsonsmeasurement.org/toolBox/tremor.htm

All you need to do is to put a finger on the pressure pad of a laptop, and it will measure the finger's movement. Unfortunately, it only gives reasonable results for some tremors. I'll be grateful for any advice on how to make it more sensitive.

John