Don't know if this applies to Prescott, but isn't there emissions testing even for older cars in AZ? Here's what I saw at the AZ emissions site:

Q: What vehicles must be tested?
A: Vehicles that are model year 1967 and newer and more than 5 years old require emissions—this includes gasoline and diesel-fueled vehicles. Alternative fuel, flexible fuel (E85) and hybrid vehicles also require emissions. Newer vehicles are exempt for the first 5 years of registration. Some vehicles may require a different schedule. If unsure, call 1-877-myAZcar (1-877-692-9227.)

Maybe a resident can chime in about it. I'd want to know if I was considering a move to AZ.