It started with the diesel smell on the streets of Beth Gardiner’s adopted home city of London, and led the former Associated Press correspondent on a world tour that ended with her book, “Choked: Life and Breath in the Age of Air Pollution.” She’s on to talk about her travels — where things are bad, and where they have gotten better. And on My Favorite Trip, actress Rebecca Rittenhouse (Four Weddings and a Funeral) talks about living in London while filming the TV series. Spoiler Alert: she won’t be seeking hazardous duty pay.