Annual chest xray (smoker) always clear no known infect in 10+yrs (last bronchitis) mild scar in left low lobe this year just show now from10yr ago?

May not be scar: Could be a tiny area of collapsed lung, called atelectasis, which is very common and benign. Also, technology keeps getting better, so the chest xrays are more detailed, especially digital radiography. Also, the scar may have been developing all along, and just became big/dense enough to see. Lastly, make sure your doctor is not concerned about the results - if they are, consider workup with ct.