I have a 21 yr old sedan that if I was in cali this would require me to go to a special emission station [higher costs] . they put it on the tread mill and check for any pollution as well as any codes or uncompleted emission tests all must be completed. then you have to show that , the cat converters are cali approved .
so in my state this 21 yr old vehicle only gets a safety inspection .. the only way it can fail is on the emissions would be a smokey exhaust.
having been to cali/az I did find vehicles not of cali reg are the ones as you mentioned , that they did put out nasty exhaust fumes. these vehicles had reg of Mexico .
up here in MA it is rare to find a polluting vehicle ,even with the reasonable emissions testing .
trucks have improved greatly on emissions up here.
if you like clean air my area is the place to live .
the HVAC has to have some outside air in any mode to keep the possibility of CO from entering the vehicle by providing a positive cabin pressure .. it is not a number that is available on passenger vehicles that I have seen but I have read this is how and why its engineered.
what are the emission testing rules in OR for a 20 yr old passenger vehicle ?