Below is information on the current background air quality in some of North America's major cities based on data taken from http://www.airnow.gov recorded at 12:30 pm GMT on May 23. 

Twitter said Wednesday it was stepping up security measures for the popular messaging service following a series of high-profile breaches by hackers hitting media organizations and others. Twitter said it would implement a new login verification system, "a form of two-factor authentication" which is "a second check to make sure it's really you" when a user signs in.

*** FOREIGN TIPS U.S. Government Urges North Korea to Free Jailed American WASHINGTON (Yonhap) -- The U.S. government called on May 15 for North Korea to release an American citizen jailed there, saying Washington's top priority is to secure the safety of its nationals. "We urge the DPRK (North Korea) authorities to grant Mr. Bae amnesty and immediate release," Patrick Ventrell, deputy spokesman for the State Department, told reporters. "There is no greater priority for us than the welfare and safety of our U.S. citizens abroad."

President Barack Obama dropped in Wednesday on a White House meeting with the secretary of Russia's Security Council to discuss Syria and counter-terrorism cooperation, the White House said. Obama joined National Security Advisor Tom Donilon at his meeting with Nikolay Patrushev, the Russian security council secretary, a spokeswoman for the National Security Council said. "The president reaffirmed his desire to strengthen the bilateral relationship, including US-Russian economic ties," spokeswoman Caitlin Hayden said.