New York and Detroit are in the top three on the list for the world's worst air pollution, as smoke from Canadian wildfires makes skies hazy in the Midwest and along the East Coast. Plus, Trump’s last chief of staff Mark Meadows testifies before a federal grand jury in the special counsel’s probe into the former president. And, Trump's former Vice President Mike Pence releases a video announcing he'll take on his old boss in the race for the White House. Also this morning: a high school graduation becomes the scene of a mass shooting in Virginia, and the Pope is in hospital, set to undergo abdominal surgery.To learn more about how CNN protects listener privacy, visit cnn.com/privacy