NEW DELHI, INDIA - NOVEMBER 8: Cyclists cover their faces to avoid pollution amid heavy smog, on November 8, 2017 in New Delhi, India. Delhi was enveloped in a thick blanket of haze for the second consecutive day with air quality levels deteriorating. Deputy chief minister Manish Sisodia says all schools to remain shut till Sunday. (Photo by Burhaan Kinu/Hindustan Times via Getty Images)
Brian Seligman holds a sign to protest a gas leak in the Porter Ranch area of Los Angeles before a meeting of the California Air Quality Management District in Granada Hills, California January 9, 2016. Southern California Gas Company has been tackling a Los Angeles-area natural gas leak that has been sickening nearby residents for more than two months. REUTERS/Danny Moloshok TPX IMAGES OF THE DAY
A man wearing a mask is seen in smog during a polluted day in Harbin, Heilongjiang province, China, December 19, 2016. REUTERS/Stringer ATTENTION EDITORS - THIS PICTURE WAS PROVIDED BY A THIRD PARTY. EDITORIAL USE ONLY. CHINA OUT.
U.S. President Donald Trump delivers remarks to U.S. troops at the Naval Air Station Sigonella to visit U.S. troops before returning to Washington D.C. at Sigonella Air Force Base in Sigonella, Sicily, Italy, May 27, 2017REUTERS/Jonathan Ernst