Data and Research. Uses the prior knowledge he has about the subject and then uses his own role in this type of situation. Ethos is where they show their own knowledge, trustworthiness, and must be credible. Think about it in an ethical format - if someone has strong ethics, they are trustworthy and have evidence to back up what they are writing about.
Explanation:
You want to read something from someone who knows about cigarette smoke and the statistics where it has hit them personally.
The author uses precise numbers implying he has done his research and knows what he is saying, and his use of vocabulary suggests he is educated on the subject and knows what he is talking about.
